بسم الله الرحمن الرحيم REFRACTION (1) Reference:

بسم الله الرحمن الرحيم REFRACTION (1) Reference:
Optometry department. The Islamic University Of Gaza. Faculty of science. REFRACTION (1) Reference: DUKE- ELDER'S Practice. .

CONTENTS CLINICAL IMPORTANCE OF REFRACTION
VISUAL ACUITY ( V . A.(Testing Testing V.A in adults : Testing V.A in preverbal children : Testing V.A in verbal children : THE TESTING OF NEAR VISION OBJECTIVE METHODS OF REFRACTION RETINOSCOPY TRIAL FRAME (T.F.) TRIAL LENSES The power of the neutralizing lens and the meridian of astigmatism. The value of spherocylindrical (s-c) combination in retinoscopy

CONTENTS REFRACTIVE STATES OF THE EYE.
The calculation of the final refraction. DIFFICULTIES IN RETINOSCOPY. Advantages of cycloplegia. Disadvantage (side effects) of cycloplegia. SUBJECTIVE VERIFICATION OF REFRACTION. ASTIGMATIC FAN. THE ELEMINATION OF ACCOMMODATION DURING SUBJECTIVE REFRACTION. STAENOPIC SLIT. BINOCULAR CORRECTION. THE ORDERING OF SPECTACLE FOR DISTANCE.

CONTENTS THE RANGE AND AMPLETUDE OF ACCOMMODATION.
FATIGUE OF ACCOMMODATION. SYMPTOMS OF FAILURE OF ACCOMMODATION. INCREASED ACCOMMODATION. DIMINISHED ACCOMMODATION Convergence.

Review of geometrical optics:
Light travels through space in straight lines. If a ray of light meets a body in it’s passage through space one of three things may happen: It may be absorbed. It may be reflected. It may be transmitted. (refracted) When the light transmits from one medium into another medium of different density, it is called to be refracted. Principles of vergence: As applied to light rays, the term vergence describes the direction of a ray as it passes between some luminous point to a lens. Vergence is the reciprocal of the distance from the lens to the point of convergence of the light. Light rays that moving away from each other are termed divergent. Light rays that are moving toward each other are termed convergent. Parallel light rays have zero vergence.

Divergent rays convergent rays parallel rays

Postpone Visual thresholds:
Visual thresholds can be classified into three groups: 1-Light discrimination :( which include brightness sensitivity, brightness discrimination, brightness contrast, and color discrimination). 2-Spatial discrimination: (which include visual acuity, distance discrimination, and movement discrimination). 3-Temporal discrimination: This refers to perception of transient visual phenomena like flickering lights.

vergence -Light rays emanating from a point source of light are divergent. -Convergent light rays do not usually occur in nature but are the result of the action of an optical system (e.g., a lens). -Light rays emanating from the sun are essentially parallel and have zero vergence. -Power (or vergence power) describes the ability of a curved lens to converge or diverge light rays. By convention, divergence is expressed in minus power and convergence is expressed in plus power. -Diopter is the unit of measurement of the refractive power of a lens and is abbreviated (D).

Postpone 1- The minimum visible:
It is an example of brightness discrimination which means the ability to detect differences in brightness of two light sources. If the target is luminous object on perfectly dark background, this measures the brightness sensitivity of the eye. 2- The minimum perceptible: It is a measure of brightness discrimination and concerned with the detection of fine objects such as dots or lines against homogenous background. 3- The minimum separable: It refers to the smallest visual angle at which two separate objects can be discriminated and depends on object contrast and packing density of photoreceptors in fovea.

Postpone 4- Vernier acuity (hyperacuity):
It refers to the ability of the eye to discriminate in spatial localization and detects misalignment of two line segments in a frontal plane if these segments are separated by as little as 3-5 seconds of arc, considerably less than the diameter of single foveal cone. 5- The minimum legible: It tests the patient ability to recognize progressively smaller letters or forms, frequently called optotypes. The angle that the smallest recognizable letter or symbol subtends on the retina is a measure of visual acuity.

CHAPTER I CLINICAL IMPORTANCE OF REFRACTION
1-Anomalies (abnormalities) of the optical state of the eye (refractive errors) are the commonest cause of defective vision (DV) thus any patient can not see clearly must undergo visual examination (refraction).

CLINICAL IMPORTANCE OF REFRACTION
2-While the near sighted (myopic) child can not see the black board clearly at school, the presbyopic person can not read the small prints clearly.

- D.V. may occur in persons having a previous visual correction using glasses or contact lenses - |The interaction between the optical anomalies of the eye and eye diseases has both diagnostic and therapeutic implications like:-

A cataract patient may have a visual acuity (6/12) that corrected up to (6/6) with glasses, is not in need for cataract surgery. Also after operation of cataract extraction (postoperative) the patient also is in need for refraction. Eye examination showed a macular lesion ,but refraction detected good visual acuity , this gives an impressionإنطباع that the macular lesion is not serious.

EYE-STRAIN,HEADACHE AND PSYCHOLOGICAL FACTORS
-1 In high degrees of refractive error the main symptom is D.V. 2- In low degrees of refractive errors the D.V. is only one of his symptoms other symptoms like effort to see clearly in spite of the presence of the refractive error.

3-Condition of sustained use of accommodation in hypermetropic persons and presbyopic persons in near work are typical circumstances that produce non-visual symptoms like eye pain and headache.

4-The fact that the pathological basis of these symptoms depend on fatigue of extra ocular muscles and intraocular muscles (like ciliary muscles) has led to the mechanical concept of the strain that named EYE- STRAIN.

CLINICAL IMPORTANCE OF 20/9/2010REFRACTION
SYMPTOMS OF EYE STRAIN: A-Visual symptoms. B-Ocular symptoms. C-Referred symptoms.

A-VISUAL SYMPTOMS These symptoms are intermittent in small refractive error like 0.50 D. astigmatism, actual visual acuity forms little or no of the symptoms in normal conditions. This defect can be compensated by the ciliary muscle effort and accommodation in normal conditions.

But in conditions of long near work and effort of study this small refractive error may result in marked symptoms. There frequently comes in periods of excessive visual strain , or during temporary deterioration of the general health , fatigue comes on both eyes and vision fails.

This is especially occurs in persons who use eyes much for reading or study of small prints for long time or sewing or watching T.V. for long time or driving in difficult circumstance and all conditions associated with attention and anxiety.

DETAILS OF VISUAL SYMPTOMS:
-Sensation of confusionاِخْتِلال ; اِرْتِبَاك . -Temporary blurring . -Tiredness of the eyes. -Heaviness of eye lid. -Sensation of weariness إِجْهاد and drowsiness. نُعَاس -These symptoms are relieved by rest but recur in continuation of the work.

CLINICAL IMPORTANCE OF REFRACTION h
In deed the ciliary muscle can compensate by exerting extra accommodation till a time will come where ciliary muscle will fail to compensateعَوَّضَ (decompensation ( and the symptoms could not be relieved easily until the patient decides to seek for treatment. 8- When reads small letters the patient sees the letters running together.

B-Ocular symptoms These together are called asthenopia. These symptoms arising from excessive work of eye muscles, in presence of a refractive error where muscle fatigue results. In long period of close work the eyes feel:. Tiredness. Hotness. Uncomfort. Temporary relief by rest. In return to near work again the above symptoms develop to eye pain.

The pain of the eyes due to eye strain is mild and achingمُؤْلِم ; مُبَرِّح but occasionally becomes severe and acute. The pain may be situated to eyes or extended (Referred) to the orbit or even to head in a form of headache. These eyes have a characteristic appearance: a-Redness and congestion اِحْتِقَان of the eyes. b-Continued rubbing of the eyes. c-The eyes are watery and may be infected, this is more noticed in children (who have a bad habit of rubbing their eyes with their unclean fingers).

C-Referred symptoms The commonest one of these symptoms is headache.
This headache is localized around the eyes (frontal) but sometimes may be temporal ,vertical or occipital. The nature of the headache is dullأَكْدَر ; أَكْمَدُ , achingمُؤْلِم , boring , deep seated or migrainous. It may be intermittent or constant , related to the amount of use of the eyes.

The aggravating factors like……eye fatigue and poor illumination are said to be common .
N.B. No case of obscureغامِض headache must be treated according to the medical lines before eliminating the refractive errors as an etiology of that headache.

2-Digestive upset (disturbance, disruptionتَعْطِيل ; عَرْقَلَة ): Like…dyspepsiaتُخْمَة and nausea. 3) Vague nervous symptoms: Like…dizzinessدَوَّخَة , insomnia أَرَق ; سُهَاد , and depression. وكآبة

CHAPTER II VISUAL ACUITY (V . A)
The V.A. is the function not only of the dioptric apparatus of the eye but also of the retina , visual pathway and central nervous mechanisms. V.A. is determined by the smallest retinal image the form of which can be appreciated , and it's measured by the smallest object which can be clearly seen at a certain distance.

VISUAL ACUITY (V . A( *In order to discriminate the form of an object its several parts must be differentiatedيمَيَّز َ. *Each 2 separate cones in the macula are stimulated (ON) while the one between them remains unstimulated (OFF).

Importance of testing Visual acuity:22/0/2010
Testing visual acuity is very important in all of the cases because of : It gives us an accurate diagnosis for the patient’s case, and indicates the severity of the problem. It may help us to discover a new problem at the patient, which is not the main problem that the patient complains from. It also help us in following up the patient's case, to compare between pre and post treatment. For all of these reasons visual acuity must be tested for all of the patients before visiting the ophthalmologist. And this is the mission of the optometrist, who is the specialist examiner in these examinations.

The average diameter of the macular cone is 0
The average diameter of the macular cone is mm ( 4 microns), this forms the smallest distance stimulated cones. The normal eye should be able to appreciate a retinal image of this size. It was found that in order to produce an image of minimal size (0.004 mm ) the object must subtend an angle of one minute at the macula and this is taken as standard of normal visual acuity .

VISUAL ACUITY ( V . A.(. These principles were included in Snellen's test types (vision charts) ,these types consist of letters of gradually decreasing sizes. Each letter is of such a shape that can be closed in a square the size of which is 5 times the thickness of the line composing the letter.

Line subtends: One minute at 60 meters One minute at 36 meters

VISUAL ACUITY ( V . A) charts

The size of the squares consisting the breadth of the lines subtend visual angle one minute on the macula when they are at a specified distance away. Each entire letter subtend an angle of 5 minutes at the same distance .

A A A 5minutes The formation of the Snellen’s test type

VISUAL ACUITY ( V . A (. The first line of the type is constructed that this angle is formed at distance of 60 ms, the second letter at 36 ms , the 3rd at 24 ms, the 4th at 18 ms, the 5th at 12 ms , the 6th at 9 ms , the 7th at 6 ms. and so

VISUAL ACUITY ( V . A.(. In some charts additional lines are inserted which subtend one minute angle at 5 and 4 meters respectively. If a person is placed at certain distance which is usually taken at 6 meters , if he has normal V.A he must read easily down to line with size 9 and the 6 size line should just be distinct.

VISUAL ACUITY ( V . A.(. If he can not reach this limit his vision is defective ( D.V ), but if he can exceed this limit ,his visual acuity is above the standard ( hyper acute). The result of the test is expressed by a fraction the numerator of which denotes the distance while the denominator denotes , the size of the letter in the seen line. Example V.A = distance / numerator = 6 size/denominator =

VISUAL ACUITY ( V . A.(. If the person can read the letter of size 6 from 6 meters his visual acuity is (6/6), if he can see the size 9 from 6 meters his V.A.(6/9), if he can see the size 12 from 6 meters his V.A. (6/12), if he can see the size 18 from 6 meters his V.A.(6/18), if he can see the size 24 from 6 meters his V.A.(6/24), if he can see the size 36 from 6 meters his V.A.(6/36), if he can see the size 60 from 6 meters his V.A.(6/60).

VISUAL ACUITY ( V . A.(. If he can see the letter of size 5 or 4 from 6 meters his V.A. is (6/5) or(6/4) respectively his vision is hyper acute but if he can not read letter size 60 he is low visioned. سبحان من قسم الأرزاق فلا عتاب ولا ملاما أعمى وأعشى وذو بصر وزرقاء اليمامة

In U. S. the metric system is not employed but the feet system is used
(6 ms=20 feet) V.A. 6/6=20/20 , 6/9=20/30 , 6/12=20/40 , /18=20/60 , 6/24=20/80 , 6/36=20/120 , 6/60=20/200. It's obvious that the corrected (aided) V.A. varies from uncorrected (unaided) V.A.

VISUAL ACUITY ( V . A.(. *In assessment of V.A. for distant the accommodation is relaxed. *When the V.A. is corrected by spectacle lenses fixed at the anterior focal point (15.7mm) the V.A. is called absolute V.A. *But the spectacle lenses are normally fixed at the B.V.D =about 12mm in front of the cornea and the V.A. is called relative V.A.

THE ROUTINE TESTING OF V . A .25/9/2010
The test type should be clearly printed . The test type should be legible . The test type should be uniformally illuminated. The distance between the patient and the chart is 6 ms or 20 feet.

VISUAL ACUITY ( V . A(. If this distance is unavailable the patient sits 3ms in front a plane mirror and the chart is fixed just behind and above the patient’s head. The patient must understand what he will see to be cooperated. The R.E. (right eye) should always be tested firstly except if the L.E. (left eye) has a complaint of D.V

VISUAL ACUITY ( V . A.(. 8.The patient reads down the chart using his right eye (R.E) OD as far as he can , then he repeats the test with his left eye( L. E ( OS. 9.Then B.E. (both eyes) are tested together (OU) (binocular V.A.), it was proved that if the V.A. in B.E. is equal they enforce each other to see an excessive line down the chart . Vr (O.D=Oculus dexter)6/9 Vl (O.S =Oculus senester)6/9 BE ( O.U =Oculus utrique) = 6/6

VISUAL ACUITY ( V . A.(. 10. If the patient can not see the largest letter 6/60, he is asked to walk one meter towards the chart and if he can read it his V.A. is 5/60 but if could not ,he walks another one meter, if can read it has V.A. 4/60 and so on (3/60, 2/60, 1/60) after 3/60 the case called legal blindness .

VISUAL ACUITY ) V. A .( 11 .If he could not see the letter 60 from a distance one meter , the chart becomes useless. 12.In a good illuminated room we ask him to count the examiner's hand fingers at 1m or less if he can , his V.A. is couting fingers (C.F.) , each eye V.A is assessed separately.

13.If he could not count fingers infront his eye, the examiner moves his fingers against a dark back ground such as his coat and ask him what can you see ,if he can see the moving fingers, his V.A. is H.M. (hand movement). 14.If he could not detect the hand movement we keep the room light off and we use a relatively faint light like that of direct ophthalmoscope and ask the patient what can you see? if the answer is seeing light his V.A. is P.L (perception of light).

VISUAL ACUITY ( V . A (. 15. In PL ,we project the same light from different directions on the same eye if the eye can see the light from these directions the V.A. is PL with good projection , otherwise PL with poor projection. 16. If he could not see the light his V.A. is NO PL (complete blindness and the eye is a hopeless eye).

VISUAL ACUITY ( V . A (. 17. The ordinary V.A. test depends upon the cooperation of the patient , thus it fails in : a- Malingerers مُتَمَارِضٌ : these could be detected by adding a high sphere lens in the trial frame say +10 Ds and ask him if he can see the chart , he will say NO then we add -10 Ds and ask him does he see, if he says YES he is malingerer. b-In illiterates أُمِّيّ : for those we use the broken ring letters (C) or (E) letter which are useful for any nationality. The patient is only asked to mention the direction of the break in (c) .

VISUAL ACUITY ( V . A (. c-Young children: for those we use the familiar, figures of varying sizes as ship- car -bird -cow –doll on the principle of (c) chart, the child has a card containing the same figures in the chart and he is asked just to mention the figure which is similar.

1- Testing V.A in preverbal children:-
Occlusion of one eye. Fixation test. 'Hundreds and thousands' sweet test. Rotation test. Forced choice Preferential looking tests. Optokinetic nystagmus drum.

1.Occlusion of one eye.27/9/2010 It is a simple method for testing the visual acuity in preverbal children and infants. We cover one eye, and If strongly objected by the child, indicates poorer acuity in the other eye . This method just indicates if the V.A is good or poor, and does not give us an accurate measurements.

2. Fixation test. This is a very good method in testing V.A, and it is performed as following: A 16 ∆ base- down prism is placed over one eye and the other is occluded with using either light source or human face (silent smile). The eye behind the prism is therefore forced to elevate, to take up fixation. The eye behind the prism is then observed. Fixation is then graded as central or non-central and steady or unsteady.

The other eye is uncovered and the ability to maintain fixation just after removal of the prism is observed :- If fixation immediately returns to the uncovered eye, then visual acuity in covered eye is impaired. If fixation is maintained after a blink. (10second) then visual acuity in covered eye is good. If the patient alternates fixation. Then the two eyes have equal vision. The test is repeated with the prism over the other eye. Monocular fixation should be central, steady and maintained in each eye .

Correlation between visual acuity and fixation patterns:
Gross eccentric fixation or affixation. 1/60 Unsteady central fixation less than 5 seconds. 4/60 Central steady fixation, but will not hold fixation when the cover removed from the other eye. 6/60 – 6/24 Central steady fixation, but will hold fixation with deviating eye when the cover is removed, but prefers fixation with other eye 6/18– 6/9 Alternates spontaneously, hold well with both eyes, both fixation 6/6 both eyes.

3.'Hundreds and thousands' sweet test:
Is a gross test which is seldom performed. In principle, if the child is able to see and pick up small sweets at 33 cm. visual acuity is at least 6/24. 4. Rotation test. Is a gross qualitative test of the ability of an infant to fixate with both eyes open. The test is performed as follows: The examiner holds the child’s facing him and rotates briskly through 360°. The child fixates moving targets behind the examiner.

If vision is normal the eyes will deviate in the direction of rotation under the influence of the vestibule-ocular response. The eyes intermittently flick back to the primary position to produce a rotational nystagmus. When rotation stops, the nystagmus should also cease due to suppression of post-rotatory nystagmus by fixation. If vision is severely impaired. The induced nystagmus does not stop when rotation ceases because the vestibulo-ocular response is not blocked by visual feedback .

5. Forced choice Preferential looking tests.
Can be used from early infancy . This behavioral technique is based on the observation that infants prefer to view a pattern stimulus than homogeneous field. Two examples are Teller acuity cards, which consist of black stripes of varying thickness and Cardiff acuity cards, which consist of shapes with variable outlines. Low-frequency (thick) gratings or shapes with a bold outline are seen more easily than those with thin outlines. And an assessment of visual acuity is made accordingly.

The test may be used successfully with other age groups. The targets are drawn with a white band bordered by two black bands. The Cardiff Acuity test is designed for acuity measurement in children aged 1 to 3 years. The targets used are pictures, all of the same size. But decreasing in width of white and black bands.

The principle of the test is that of preferential looking, a young child will choose to look towards a target rather than a plain stimulus. In the Cardiff Test, each target is positioned either in the top half or in the bottom half of the card. If the target is visible the child will look toward it, and the examiner, watching the child’s movements, can judge the position of the target from those eye movements. An important feature of the preferential looking technique is that the examiner should not know in advance the position of the target.

6- Optokinetic nystagmus drum.
Standardized drums that contain stripes, which subtend small fractions of the infant's visual field, are available. May provide an estimation of visual acuity dependent on the size of the stripes used (alternating black and white strips with sharp, distinct interface) that frequently are spun at varying and uncelebrated rates, and are bathed in variable illumination. This method measures acuity by means of a motor response technique (eye movement) .

2.Testing V.A in verbal children :
Allen picture cards (Kay pictures). The Sonksen-Silver test. “HOTV test.” Sheridan –Gardner test. Landolt rings (C). Familiar tumbling E test.

1. Allen picture cards (Kay pictures).
Are quite useful, the near test card is slightly easier for the younger child, but have certain disadvantages: Pictures are not constructed according to the Snellen form (each element in the target subtended 1 minute of visual angle). Some pictures are not familiar to the child e.g. telephone. Pictures are variably larger than the corresponding Snellen letter target. Smallest target size is labeled 20/30=6/9. Despite these difficulties, most children respond readily to this familiar and easily obtainable test.

2. Sheridan _ Gardner test.
This method requires children to match familiar object patterns viewed at distance with those on a near card. Some children respond to isolated Snellen optotypes, or graded numerical optotypes, before linear Snellen presentations.

3.The Sonksen-Silver test. “HOTV test.”
The HOTV test requires pattern recognition and matching of progressively smaller optotypes with those on a hand –held card. These letters are chosen to be of average recognition difficulty and have a vertical axis of symmetry, which obviates the issue of right –left confusion so common in this age group. An advantage is the exact correspondence of the target to the graded Snellen optotypes

Which is better??? The main deference between the Sheridan _ Gardner test and the HOTV test is that there is no crowding phenomena in the Sheridan _ Gardner test, because it show a single optotype in each card. so it is not accurate to test an amblyopic child with the Sheridan _ Gardner. Because the crowding phenomena is the hallmark to the presence of amblyopia , so it is very important to use these two tests in the correct way and on the suitable patients .

4. Landolt rings (C). Discontinuous circles, the child points to a similar ring on a hand –held card. The test often confuses the younger child and perhaps is more useful for illiterate adults; it does have the advantage of corresponding directly to the Snellen chart. 5. Familiar tumbling E test: Requires matching orientation of the letter E with a figure or the child's fingers, unfortunately, right-left disorientation is common in this age range and limits the usefulness of the test. Its major advantage is the direct correspondence to graded Snellen optotypes.

Important notes: In some cases, the patient may have a latent nystagmus, which appears when the other eye is occluded. The latent nystagmus reduce the V.A due to the inability to fixate the target. In these cases when testing V.A, we must occlude the eye in a way that’s prevent the latent nystagmus to occur.

There is three methods to perform that:
Using a D in front of the eye, it will reduce the vision in a marked limit and in the same time it will not produce nystagmus. By putting the occluder in front of the eye at a distance nearly 10 cm, in this way we occlude the eye and prevent the nystagmus. By using the frosted lens. This lens is present in some trial cases. This lens permits some light to enter the eye but it also occlude the eye from seeing any thing. And so no nystagmus will occur.

THE TESTING OF NEAR VISION
(N.V) 1.This occurs at a distance of 30-40cm that called the reading distance (working distance). 2.The first test of this kind was constructed by Jaegar in 1867 , it consists of the ordinary print fonts (complete set of type {Printing} ) of varying size as use at that time. 3.Recently a new test card which , approximate Jaegar original choice are used.

Jaegar N.V chart J8 أعمى وأعشى وذو بصر وزرقاء اليمامة

THE TESTING OF NEAR VISION (N.V)
4.These are traditionally called J1 ,J2, J3, J4, J5…….they are sufficient for accurate practical purpose. 5.In testing N.V. the patient remains , seated on the chair, with a good light thrown over the left shoulder and he is asked to read at the known reading distance . 6.The N.V. is recorded as J1 for the smallest line ,J2 follows it ,J3….J4. 7.Each eye is tested separately .

OBJECTIVE METHODS OF REFRACTION
I)- RETINOSCOPY :- 1.It's the most valuable method of estimating the optical state of the eye , it's useful and accurate up to (0.25D) correction. 2.In retinoscopy an illuminated area of the patient's retina acts as an object in dark room that reflects the light to be seen on the patient's pupil as red reflex. 3.If the image ( I ) formed between the eyes of patient and the observer the red reflex (R.R) moves opposite to the movement of the retinoscope. (The patient had a high myopia > 1.5 D)

Retinoscope In high myopia: Ho Ro Hs Rs I1 No I Ns Image m

Retinoscopy against movement

I- RETINOSCOPY 4. If the image is formed behind the eye of the observer (low myopia) or the eye of the patient (hypermetropia) the red reflex moves with the movement of the retinoscope .

Hypermetropia Ho Ro Rs Hs image A O1 Fs No NS I1 o I I B

In low myopia The image lies behind the retina of the observer image
Ns No Ro Rs Hs Ho I I1 The image lies behind the retina of the observer image

I- RETINOSCOPY 5.When the far point of the patient's eye corresponds to the nodal point of the observer's eye the neutral point ( end point ) is reached , where no movement of red reflex is noticed.

I- RETINOSCOPY 6.The working distance between the eye of the examiner and the eye of the patient , and is the reciprocal of the power in diopteres which should be deduced from the power of the lenses that were added during retinoscopy to reach the neutral point (N.P.) If the W.D. is 2ms we deduce 0.50D. If the W.D. is 0.5ms we deduce 2.00D. If the W.D. is 1m. we deduce 1.00D.

I- RETINOSCOPY 7.The rational ; مَنْطِقِيّ is to add lenses to the dioptric system of the patient's eye until the neutral point is observed by the observer. 8. At neutral point the patient's eye refractive error is measured by the added lenses minus the reciprocal of the W.D. in diopters. 9.The farther away the observer from the patient's eye the more accurate is the result obtained , but in practice this is counterbalanced by the difficulty in seeing the red reflex.

METHODS OF RETINOSCOPY
A) CLASSICAL RETINOSCOPY= REFLECTING RETINOSCOPY : 1. It consists of a separate source of light which is bright, narrow and fixed behind and above the shoulder of the patient . 2.The observer catches a perforate mirror with a central opening not less than 4mm in diameter . 3.This plane perforated mirror reflects the light from the source into the patient’s eye which sends the image that can be seen by observer's eye as Red reflex (R.R) through the central opening .

REFLECTING RETINOSCOPY
4.Movements of the illuminated area of the patient's retina are produced by tilting the mirror. 5.The used mirror may be plane or concave but the plane one gives a better result.

B) LUMINOUS RETINOSCOPY :Advantages:-
1.In which both of light source and mirror are incorporated . 2.It's standard modern instrument , easily manipulated with the advantage that the intensity and type of the beam can be readily controlled. 3.It's portable.

streak retinoscope 4.It contains a strong convex lens for condensation of light in the patient's eye. 5.The most ocular luminous retinoscope today is the streak retinoscope as it produces more easily recognized R.R. it also allows the axis of the meridian of astigmatism to be more readily identified separately.

streak retinoscope 6.Even greater efficiency is obtained from the modern retinoscopy by the use of halogen bulbs and rechargeable batteries.

TRIAL FRAME (T.F.) T.F. is used to carry the trial lenses during
objective and subjective refraction . 2.T.F. should be clean , light and easily adaptable allowing the adjustment for each eye separately. 3-These are essential necessity so that the trial lenses where in place are fixed at standard distance from the eye (B.V.D) back vertex distance about 12 mm. and are accurately centered.

TRIAL FRAME (T.F.)

TRIAL FRAME (T.F) 3.Anteroposterior adjustment is possible as well as vertical , and horizontal adjustments . 4.The dial (rotatable disk ) indicating the orientation of the frame is truly positioned to avoid the mistakes in reading the axis of the astigmatism if present.

TRIAL FRAME (T.F) 5.Simplicity to ensure (make certain) , lightness ,and comfort fitting nose rest are of greatest importance as some patients are very sensitive to weight which may lead to annoyance and loss of the patient's cooperation.

TRIAL FRAME (T.F) 6 .Each eye of trial frame is supplied by 3 cells (compartments): the first is the nearest to eye is used to carry the spherical lenses . the middle to carry the cylindrical lenses and the farthest one to carry the accessories like occluder , pinhole , staenopic slit, filters, prism……etc 7.These cells should be close together as possible as a considerable space between the lenses may result in some errors in results.

TRIAL FRAME (T.F) 8.The T.F. should have its side pieces joined so that when the near vision (with shorter interpupillary distance) tested by reading the glasses can be angled so that their optic axes correspond to the downward inclination مَيْل of the visual line.

اتَّبِعُونِي يُحْبِبْكُمُ اللَّهُ
علامة محبته صلى الله عليه وسلم: إن من أحب شيئاً آثرَ موافقته، وإلا لم يكن صادقاً في حُبه، وكان مُدعياً، فالصادق في حب النبي صلى الله عليه وسلم من تظهر علامة ذلك عليه: وأولها: الإقتداء به، واستعمال سنته، واتباع أقواله وأفعاله، وامتثال أوامره، واجتناب نواهيه، والتأدب بآدابه في عُسره ويُسره، ومنشطه ومكرهه، وثانياً: إيثار ما شرعه، والحض عليه وتقديمه على هوى نفسه وموافقة شهوته. وثانياً: إيثار ما شرعه، والحض عليه وتقديمه على هوى نفسه وموافقة شهوته. وشاهد هذا قوله تعالى: { قُلْ إِنْ كُنْتُمْ تُحِبُّونَ اللَّهَ فَاتَّبِعُونِي يُحْبِبْكُمُ اللَّهُ} ( آل عمران: 31)

1. A typical trial set of lenses contains plus and minus spheres every 1/4 of diopter to 4Ds (0.25, 0.50, 0.75, 1.00, 1.25, 1.50, 1.75, 2.00, 2.25, 2.50, 2.75, 3.00,3.25,3.5,3.75,4 Ds) 2. Then plus and minus spheres every 1/2 to 6Ds (4.50, 5.00, 5.50, 6.00 Ds.) 3.There after plus and minus spheres every 1 to 14 Ds : (7.00, 8.00, 9.00, 10.00, 11.00, 12.00, 13.00, 14.00Ds) 4.Then plus and minus spheres every 2 diopters to 20 Ds (16.00, 18.00, 20.00) Ds. TRIAL LENSES

TRIAL LENSES TRIAL LENSES Plus cylinder Minus cylinder Plus sphere

TRIAL LENSES 2.It also contains plus and minus cylinder every 1/4 to 2Dc (0.25, 0.50, 0.75, 1.00, 1.25, 1.50, 1.75, 2.00Dc) Then every 1/2 to 6 Dc. (2.50, 3.00, 3.50, 4.00, 4.50, 5.00, 5.50, 6.00)Dc. 3.By a combination of sphere and cylinder an excellent range of optical effect is obtained.

TRIAL LENSES 4. The trial set contains also prisms up to 10 DP then 15 and 20 DP. (1.00, 2.00, 3.00, 4.00, 5.00, 6.00, 7.00, 8.00, 9.00, 10.00, 15.00, 20.00)PD. 5.It also contains accessories as plano lenses ,opaque (occluders), pin hole, staenopic slit discs , Maddox rod , red and green filters, centering devices and others.

TRIAL LENSES 6.All these items (1-5) are included in a trial case. صَنْدَوقَ 7.In the interest of accuracy the effective power of the trial lenses should be as closely as the type of the lens which should be used in the spectacle .

6/10 8. The effect of spectacle lens is determined by its back vertex power and this varies with its position infront of the eye and its thickness. 9.Thus the back of the trial frame should occupy as nearly as possible the position of the spectacle lens which must be chosen just to clear the eye lashes averaging about 12mm infront the cornea.

TRIAL LENSES 10.Obviously we can not stand several lenses in T.F. in the same plane (cell) thus the ideal test lens should therefore be calibrated (adjusted) accurately as individual lenses but should indicate the effectivity of the lens in the plane, so that the effective power of a combination of lenses in the T.F. will correspond additively to that of a single lens in one plane.

TRIAL LENSES 11.The test lenses should also conformمطابقا , so far as possible in form and thickness to the spectacle lenses to be worn. 12. In T.F. the plane surfaces of the spherical lenses, should be where possible (fixed) next to the eye.

TRIAL LENSES 13. The rim إِطارُ; حَافَة of the trial lens should be mounted so that as near as possible in the plane surface.بدون ميل 14.Before using the retinoscope the T.F. must be accurately centered so that the optical center of any lens lies up on the visual axis of the patient's eye. تطابق تام

حب رسول الله صلى الله عليه وسلم
وعن أنس رضي الله عنه أن رسول الله صلى الله عليه وسلم قال: " لا يؤمن أحدكم حتى أكون أحب إليه من نفسه وماله وولده ووالده والناس أجمعين "، أخرجه البخاري ومسلم.

حب رسول الله صلى الله عليه وسلم
وفي حديث عمر: " أنت أحبُّ إليّ يا رسول الله من كل شيء إلا نفسي التي بين جنبي. فقال له عليه الصلاة والسلام: لا تكون مؤمناً حتى أكون أحب إليك من نفسك، فقال عمر: والذي أنزل عليك الكتاب، لأنت أحبُ إلىَّ من نفسي التي بين جنبي، فقال صلى الله عليه وسلم: " الآن يا عُمُر تم إيمانك "، أخرجه البخاري.

TRIAL LENSES This is obtained by measuring the
inter pupillary distance IPD of the patient using a ruler or using 2 centering devices and the light reflex on both cornea and the scale above the eyes. Autorefractometer also can give the IPD.

THE PRACTICE OF RETINOSCOPY
1.The room should be long and darken to relax the accommodation of the patient’s eye. 2.The patient is instructed to look past the head of the examiner in a direction opposite to that of the examined eye. 3.The accommodation of the examined eye must be relaxed , this is obtained by:-

a) Fixation a spot light on the opposite wall and to ask the patient to fix on it . b) In absence of such a light we ask the patient to look close observer’s ear and far away. c) In children, we must use cycloplegia for accurate refraction (temporary paralysis of ciliary muscle) , and then it is not important if the child fixes on the light of retinoscope.

4.In either event , in cases of squint one or either eye should be occluded to avoid the deviation of the examined eye. 5.Ideally , the examiner should use his right eye to examine the right eye of the patient and his left eye to examine the left eye of the patient to minimize the eccentricity. اِنحراف

6.The examiner fits the T.F. on the patient’s face with trial lenses near at hand , setting facing the patient at a chosen distance (working distance) usually equal , the length of arm 2/3m. 7. The examiner directs the light of the retinoscopy into the pupil of the patient .

8.Slow tilting of the retinoscope is started , noting the red reflex regarding:- A )The direction of movement of red reflex either with or opposite to the direction of light of retinoscope. B )Does the plane of movement of the red reflex parallel to the external movement (in astigmatism it is not parallel). C )The speed of movement of the red reflex. N.B.: Speed of movement of the red reflex is inversely proportional to the quantity of refractive error .تناسب عكسي

أدب رسول الله صلى الله عليه وسلم
وعن عائشة رضي الله عنها رَوَت أنَّ اليهود أتوا النبي صلى الله عليه وسلم، فدار بينهم الحوار الآتي: - اليهود: السَّام عليك، (أي الموت عليك). - الرسول صلى الله عليه و سلم : وعليكم. - عائشة: السَّام عليكم، ولعنكم الله وغَضِبَ عليكم !. - الرسول صلى الله عليه وسلم: مهلاً يا عائشة! عليكِ بالرِّفق، و إيَّاكِ و العنف و الفُحش . - عائشة: أوَلم تسمع ما قالوا ؟!!. - الرسول صلى الله عليه و سلم: أوَلم تسمعي ما قُلت، رددتُ عليهم، فيُستَجاب لي ولا يُستَجاب لهم فيَّ. وفي رواية لمسلم: (لا تكوني فاحشة، فإنَّ الله لا يحب الفُحش والتَّفَحُّش).

The power of the neutralizing lens and the meridian of astigmatism
1. The great majority of refractions are cases either without astigmatism (spherical refractive error) or with regular astigmatism (cylindrical refractive error) in which the principal meridians are perpendicular to each other.

2. The minority of refractions consists of irregular astigmatism (in which the principal meridians are not perpendicular to each other ) . 3.In spherical errors the retinoscopy will show a neutral point which is the same in all meridians , the result is no movement in all meridians using the same lens.

4. In astigmatism the situation is not quite. 5. The refractionist has to determine not only the neutral point of the major and minor meridians of the cornea but also the relation of those regarding the difference.

6. The relationship of the direction of the external movement to that of the red reflex has an important role on the last matter (result).

7. The initial examination with retinoscope is always exploratory to determine the direction of the movement of the red reflex. The observer starts with vertical then with horizontal movement and lenses are inserted to determine the neutral point in each meridian separately.

8. If this is not so (corresponding) then the reflex may alter its plane of movement indicating the presence of astigmatism which is oblique. 9. In this case the examiner must again explore different planes of external movement of his light until it corresponds to those of red reflex .تطابق بينهما

10. In presence of astigmatism, neutralizing lenses are now found in these new meridians starting with the meridian that is less ametropic . 11. Whether with or against movement is obtained initially depends on the optical power of the eye. Oblique reflex Straight reflex

12. With the examiner arm's length away from the patient 2/3 meter. With movement is obtained in any meridian which is (emmetropia, hypermetropia, myopic less than -1.50D) in such cases we add convex lenses of gradually increasing power until neutral point is reached.

With movement

Against movement 13. If an against movement is obtained in any meridian this has myopia > -1.50D and we insert concave lenses until neutral point is obtained. Add concave lenses of increasing power until neutral point is reached.

No movement 14. If no movement of red reflex is obtained (neutral point is reached without any lenses) that meridian has myopia= -1.50D.

15. Neutralization itself is confirmed by filling of the pupil with light , or the pupil becomes totally dark in such a way that examiner is impossible to say whether the movement of red reflex is with or against.

16. The approach of neutralization as the trial lenses are changed is known by an increase in speed of the movement of red reflex but if the used lens is a long away from the neutral point the reflex will be slow .

17. In high degrees of ammetropia the red reflex without lenses may be extremely faint and becomes recognizable if a high plus or minus spherical lens is interposed. أَدَخِّلت

18. Neutralization can be altering the working distance if the examiner bends forward , from the position of neutral point with movement will be obtained , and bends away from the position of the neutral point against movement will be obtained.

19. If marked oblique astigmatism is present then horizontal and vertical movement of the retinoscope will produce oblique moving reflexes , and the external movement is adjusted عَدَّلَ ; كَيَّفَ ; لاءَمَ to correspond to these meridians a characteristic form of neutralization is seen.

marked oblique astigmatism

What is the difference between the meridian and the axis
The meridian is the line that we are moving the streak along. In the example to the left, we are streaking the 180 degree meridian. The axis depends on whether we are using plus-cylinder or minus-cylinder. The power at which equals zero.

Recognizing the presence of astigmatism
When you begin retinoscopy on an eye, you will know that there is astigmatism present in the following situations: - 1Streaking one meridian gives you with-motion or against- motion, and streaking the meridian 90 degrees away gives you a neutral reflex.

2-Streaking one meridian gives you against- motion, and streaking the meridian 90 degrees away gives you with- motion. - 3Streaking one meridian gives you with-motion (or against- motion) with a wide streak reflex, and streaking the meridian 90 degrees away gives you the same motion but with a narrower streak reflex.

As we add plus sphere power, the reflex at 90 narrows and the reflex at 180 quickly widens and reaches neutrality.

It is easiest to practice retinoscopy on younger adults, ages 20 to 50. They usually have:- clear media relatively relaxed accommodation, a definite refractometric endpoint with which to compare your retinoscopy.

As stated earlier, there is more than one way to perform retinoscopy
As stated earlier, there is more than one way to perform retinoscopy. If you get advice from different sources and mix up your technique, you will become confusedمُشَوَّش ; مُضْطَرِب . The technique described here is relatively simple and is very accurate. Once you have mastered the routine, it will become second nature and you will be able to perform retinoscopy very quickly. Practice, practice, practice.

The value of spherocylindrical (s-c) combination in retinoscopy
1. Spherical lenses may be used through out the examination , and the final correcting lenses found from the power of two principal meridians. 2. The direction of the axis of the cylinder being examined is more accurate , if the first meridian is corrected with spherical lens and the second with cylindrical lens.

The value of spherocylindrical (s-c) combination in retinoscopy
3. The strength of spherocylindrical combination can be verified if the examiner moves to ward or away from the patient to confirm his neutralization. 4. A further advantage of using spherocylindrical lenses together is in verifying the position of the axis of the cylindrical lens.

Procedure for neutralizing an astigmatic eye
The first step is to neutralize one of the meridians. You will be adding plus sphere power and streaking each of the primary meridians after each power change. The meridian with the narrow, fast reflex will neutralize first. This meridian will be 90 degrees away from the meridian with the widest, slowest streak reflex.

2. The next step is to confirm/identify the axis of the astigmatism
2. The next step is to confirm/identify the axis of the astigmatism. We have a good idea of what the second axis is from the neutralization process. When working in plus cylinder, we will line up our cylinder axis with the orientation of the streak. The axis will be 90 degrees from the meridian with the most defined with-motion streak reflex. مع الضوء

Procedure For neutralizing an astigmatic eye
If we are using a minus-cylinder, we will line up our cylinder axis perpendicular to the orientation of the streak. In other words, at 90 degrees in this example عمودي على الضوء we are streaking the 90 degree meridian, and the axis of the correcting minus-cylinder will be 90 degrees.

The final step is to subtract for our working distance. This is usually 1.50 D and it is subtracted from the sphere power only. Suppose our objective result was -1.00/-1.50x900 when we have finished neutralizing the astigmatic meridian. We then would subtract D sphere power for a final retinoscopic estimate of -2.50DS/-1.50DCx90.

Once we have a neutral reflex, we have reached the endpoint. Neutrality can be assumed when any motion just disappears. This is preferable to relying on recognizing a neutral reflex, because the reflex may appear neutral over a wide range of power settings.

REFRACTIVE STATES OF THE
EYE 1.In the normal eye (emmetrope) parallel rays are focused sharply on the retina. 2. When the relaxed unaccommodating eye is unable to bring parallel rays from a distant object into focus on the retina, eye is said to be ametropic.

REFRACTIVE STATES OF THE EYE
There are three basic conditions for ammetropia:- a) Myopia (near sightedness) in which he has an excessive convergent power of the cornea and lens making the light to focus in front of the retina and the error is corrected by using diverging (-) lenses.

REFRACTIVE STATES OF THE EYE Myopia

b) Hypermetropia (far sightedness):
eye has an insufficient converging power to focus the light rays on the retina thus the incident parallel rays come to focus behind the retina , we use converging (+) lenses to correct hypermetropia.

c) Astigmatism: the cornea and some times the lens may not have the same curvature
(radii of curvature) in all meridians the observation that result from corneal or lenticular surfaces irregular power of meridians called astigmatism.

REFRACTIVE STATES OF THE EYE
In most patients if the stronger ( steeper or more curvature ) meridian at or close to 90 degree (astigmatism with the rule) or stronger at or close to 180 degree (astigmatism against the rule). In clinical practice pure astigmatism is corrected with cylindrical lens but in many cases the condition is combined of myopia and astigmatism or hypermetropia and astigmatism , in such cases we use spherocylindrical combination in correction.

The calculation of the final refraction
1. This is obtained by deduction of a dioptric value corresponding to working distance. Thus for a working distance 2/3m = arm's length we must deduce 1.50D. 2. Suppose that in right eye one meridian is neutralized with +4.00Ds and the perpendicular meridian with +6.00Ds. . (-1.50D)

3. After orientation تمام العملthe power of the refraction in that eye is +2.50Ds/+2.00Dc x 180ْ .
4. Transposition of the lenses gives +4.50Ds/-2.00Dc 90ْ. 5. If the other eye is -1.00Ds/+1.50Dc 90ْ, Transposition of lenses gives:- +0.50 Ds/-1.50Dc x180ْ +3.0 +1.50 - 1.0 +0.50

The calculation of the final refraction
6. In the event that the 2 meridians are not perpendicular it's possible to calculate a suitable spherocylindrical optical equivalent special in contact lenses. Spherocylindrical optical equivalent=Sphere power +Cylinder power/2. 7. The recording of retinoscopic result is usually done in form of a cross which indicates the neutral point of the meridians and other orientation

SUBJECTIVE VERIFICATION OF REFRACTION
For distance vision:- 1. In the great majority of cases the refractionist should aim at getting the vision up to 6/5. 2. If he can not, he must find the cause of defect ophthalmoscopically (by use of an ophthalmoscope ). 3. Even in absence of eye pathology in the media or fundus high hypermetropia or high astigmatism often don't reach full correction.

4. A pin hole test may give some indication of the best vision attainable َ أَدْرَكَ with lenses if the condition is solely (purely) refractive error. 5. When retinoscopy has been completed the test types (chart) are illuminated and the visual acuity is tested with the trial neutralizing lenses after deduction the power corresponding to working distance.

6. Each eye is treated separately , while an opaque disc (occluder) is placed in the trial frame to cover the unexamined eye. 7. The patient is asked to read the test types from up downwards and the effect of slight modifications in the lenses are tried and small change in lenses may give a marked improvement in visual acuity.

8. Alternation of the spheres is tried first, this can be done by various ways:- a- Rapid changing of the spherical lenses , to one slightly stronger or weaker is common. b- Alternatively , a weaker sphere may be hand held in front of the trial lenses and any improvement in visual acuity with it is gauged (inserted).

A raw of weak spheres (-0.25, -0.50, +0.25, +0.50) which can be quickly moved over the front of the trial lenses and when the best combination is found the strength of the sphere in the trial frame is changed.

18/10/2010 The verification of cylinder is not so easy because there are two factors:- a- Axis of the lens. b– Power of the lens. .

a- it's better to check the axis first and this can be done most simply by rotating the cylinder lens in steps of 5 then 10 degrees in either direction and asking the patient if he finds any improvement in visual acuity, If he says yes we move the axis of the trial cylinder to the new position.

b- Verification of the power is done holding a weak cylinder(-0.25,-0.50 or +0.25,+0.50DC) in front of the trial lens , first with the axis parallel then with the axis perpendicular to the axis of trial lenses and asking the patient about the improvement in his visual acuity, then spherocylindrical combination is properly adjusted in presence of vision improvement.

BINOCULAR CORRECTION 1)When we have arrived at the final verified correction for the refraction of each eye separately , binocular vision (OU) is tested. 2)It will usually be found that an additional +0.25Ds is usually easily tolerated. 3)The test is carried out at 6 meters distance instead of infinity.

BINOCULAR CORRECTION 4) On the basis of distant correction full correction up to plus or minus 5Ds is ordered. 5) Each of back vertex distance and inter pupillary distance are adjusted to be as close as that in the spectacle lenses. 6) Before prescription binocular correction must be comfortable with equal visual acuity in both eyes, no blurring in any eye and no diplopia.

THE ORDERING OF SPECTACLE
FOR DISTANCE 1) The fullest correction consistent مُتَجَانِس with good vision should be ordered especially in low degrees of ammetropia and when the symptoms are related to eye strain rather than defective vision. 2)It will be remembered that in very high degrees of ammetropia, especially in myopia , the full correction may not to be tolerated , and an under correction is usually necessary.

THE ORDERING OF SPECTACLE FOR DISTANCE
3) In hypermetropia and in intermittent use of the glasses the full correction is more tolerable. 4) When the cycloplegic or mydriatic drops were used during refraction a deduction of lenses equivalent to ciliary muscle activity should be done according to age to allow the reactivation of the ciliary muscle which was in paralysis.

DIFFICULTIES IN RETINOSCOPY
1. Some refraction , are easy while others are extremely difficult. 2. Retinoscopy is an art which requires painstaking مُثَابَرَة ; مُوَاظَبَة practice and can not be learned in one day. 3. It's essentially practical and can not be learned from text books but only under careful supervision.

A- Difficulties due to inadequacy of technique:- a) The subjective refraction will reveal
uncorrection of visual acuity and unacceptance of the lenses by the patient. Such state of affairs commonly result from the mistake of an inexperienced (unpracticed), refractionist. b) It's important to keep a suitable working distance to ensure that retinoscopic examination is performed close to the visual axis in order to refract the macula.

DIFFICULTIES IN RETINOSCOPY
c) In this respect not only the horizontal orientationمُتَّجَه to be noted but also the vertical one. Failure to observe this fact may falsely introduce or exaggerate a cylindrical element during retinoscopy.

B- Difficulties due to absence of relaxation of accommodation of the examined eye:-
The accommodation must be inactive during retinoscopy, this is obtained by using 2 tricks: 1) Fogging of retinoscopy by inserting a high convex lens Ds in the trial frame in front of the examined eye and asking the patient to look far away at infinity, then replacement of the lenses in the trail frame as retinoscopy proceeds is always done so that neither examined eye is exposed to light without a lens before أمام, and new lens is inserted then the replaced lens is removed.

( paralysis of the ciliary muscle ) is used.
The accommodation must be inactive during retinoscopy, this is obtained by using 2 tricks: 2) To get the patient to close then to open his eyes , inspecting his eye by retinoscopy just he opens his eyes. If the above two tricks fail to relax the accommodation especially in young persons and children cycloplegia ( paralysis of the ciliary muscle ) is used.

Advantages of cycloplegia
1. Paralysis of accommodation to make easy retinoscopy. 2.Pupil dilatation (mydriasis) leads to good visualization of red reflex. 3. Macular refraction is more accurate.

Disadvantage (side effects) of cycloplegia
1. Dilated pupil alters the optical properties of the optical system of the eye, the resulting observations are due to different refractions of the lens (as the rays pass in periphery and the central area of the lens) lead to some % of errors due to different refractions. 2.During cycloplegia there is paralysis of the parasympathetic nerve supply to the lens capsule with loss of it's ability to change the shape of the lens matter leading to loss of accommodation till the tone is replaced.

Disadvantage (side effects) of cycloplegia:
3. Pupil dilatation may result in acute angle closure glaucoma (ACG) in some persons who have a narrow angle of anterior chamber especially in those 40 years old or more , this complication must be taken in consideration before instillation of the mydriatic drops especially patient having high degree of hypermetropia. .

It's better to use short acting mydriatic like cyclopentolate than long acting one like atropine As prophylactic method it's better to instill miotics like pilocarpine drops 2% after finishing the refraction under cycloplegia.

The accommodation must be inactive during retinoscopy, this is obtained by using atropine 23/10/2010in young children: 3)In young children nothing is effective like atropine (most potent cycloplegic and mydriatic) given as drops or ointment 1% twice daily for 7days (1 × 2 × 7) or thrice for 4 days or (1 × 3 × 4) , the use of atropine is mandatoryإِجْباريّ in children having convergent squint under 7 years.

In young myopes cycloplegia is not necessary as their accommodation is easily relaxed. Spectacle can be carried out on the lenses of subjective test then a next follow up visit is necessary for new assessment for aided visual acuity.

It was found that 1% cyclopentolate drops (short acting cycloplegic) are a good alternative for atropine (long acting cycloplegic) and have the following advantages: - a-Rapid onset 15 minutes . b-Short duration 8 hours. c-Relatively weaker mydriasis. d- Relatively weaker cycloplegic effect. e-The examination is done within one hour(2-3 drops given frequently every 15 minutes ).

Disadvantage (side effects) of atropine cycloplegia
Atropine (long acting cycloplegic) has some rare side effects like :- 1- Fever, more common in infants and young children . 2-Hypersensitvity in face (swelling , redness) and skin urticaria. 3-Long pupil dilatation with blurring of vision. 4-Long ciliary muscle paralysis with inability of close work. Such side effects are absent in cyclopentolate.

To decrease these side effects the puncta are closed by fingers or special synthetic plugs ,or the eyes are gently closed for five minutes to prevent absorption of atropine from the vascularبالأوعية الدموية غنيmucous membrane of the nose to enter the systemic circulation.

1-Abnormaly active accommodation.
In older patients over 20 years , the routine use of cycloplegic drops had stopped except in :- 1-Abnormaly active accommodation. 2-Marked difference between objective and subjective refraction. 3- In accommodative asthenopia. 4-Narrow pupil with difficult retinoscopy. 5-Disputed متغير refraction (controversial ) as no comfort with many lenses used before. 6-Mydriatics and/or cycloplegic are necessary in adults for detailed fundus examination or preoperative for intraocular surgery.

I) Fainting of red reflex causes :- 25/10/2010
C-SPECIAL DIFFICULTIES IN RETINOSCOPY I) Fainting of red reflex causes :- 25/10/2010 a) Opaque ocular media: 1-In corneal leucoma . 2-Blood in anterior chamber (hyphema). 3-Lens opacities ( immature cataract). 4- Vitreous bleeding ( mild vitreous haemorrhage). 5- Retinal detachment.

Corneal leucoma

Retinal haemorrhage Retinal detachment

Keratoconus

b) Very high refractive error:-
Like high myopia or high hypermetropia. In such cases we add high spherical lens either plus or minus (10Ds) to recognize red reflex then we complete the refraction as usual .

II) Variationتقلب; تغيير of red reflex in different parts of the dilated pupil:-
* The central part being different from the periphery. * This variation is accentuatedمُشَدَّد by the dilatation of pupil (mydriasis). * This is due to spherical aberrations tends to cause an increase in the brightness of the center or the periphery of the pupil , depending on whether the aberrations are negative ( In HM) or positive (In myopia).

Spherical aberrations
F1 F2 F4 F3

- Negative aberration (the periphery is faint and the center is shiny) in hypermetropia.
flat F1 F2 Hypermetropia

Positive aberration (the periphery is shiny and the center is faint) in myopia.

* Even in dilated pupil of an emmetropic
eye these variation are considerable. * these variations increase markedly in lens sclerosis in old age.

c) Scissor shadow:- * When a mixed aberrations (negative and positive ) occurs so that one 1/2 the reflex differs from the other half in its refractivity, 2 band reflexes appear which move towards and away from each other like the blades of scissor. The optics of the phenomenon wherein one part of the aperture is relatively myopic and the other hypermetropic (mixed and irregular astigmatism).

Scissor shadow Scissor shadow presents in:
1-Such an appearance appears at neighborhood of the neutral point and is common in corneal scars . 2-An irregular astigmatism like in keratoconus (irregular myopic astigmatism) may give the similar shadow. The blades of the scissor point to the scar . The best way to arrive to approximate correction is to find the lens which causes the two portions to meet in the center of the pupil.

d) In children retinoscopy may have different grades of difficulty:-
In older children cooperation is available regarding the (distance fixation – opening of the eyes – and facing of the examiner). Younger children may not pay any amount of cooperation (uncooperative ) in such cases cycloplegia is mandatory , but if no cooperation was obtained ,retinoscopy under general anaesthesia is done .30/10/2010

Atropine cycloplegia is preferred.
During child examination the trial lenses may be put in trial frame or hand held.. Very young infants are often more cooperative than those in the 18 months to 3 years old . Particular difficulty may arise in squinting children, in such cases:- Atropine cycloplegia is preferred. Unexamined eye must be covered to allow the examined eye to have central fixation. General anesthesia may be necessary in uncooperative children. 4. Fundus examination is better to be done in both eyes after objective retinoscopy.

e) In immature cataract very confused reflexes are often obtained :
Neutralization is obtained only for one meridian , the perpendicular one is indeed too abnormal, in such cases spherical lenses is used to correct one meridian while the other is tried to be neutralized by cylindrical lenses via retinoscopy or if impossible via trial and error technique. The final correction for cataract is done subjectively.

THE ELEMINATION OF ACCOMMODATION DURING SUBJECTIVE REFRACTION
1) In order to induce relaxation of accommodation without cycloplegia , it's better to make the eye artificially myope by adding relatively strong convex lens . 2)This forms the basis of various fogging methods of the subjective estimation of refraction.

3) When the refraction has been measured objectively and the visual acuity is determined 6/6 in each eye the correcting lenses are left in place and with both eyes uncovered sufficient convex sphere, say +4.00Ds are added in front of each eye to make the visual acuity less than 6/60.

4) The patient remains wearing these convex lenses for some time while looking at infinity to relax his accommodation completely . 5) The strength of the added sphere in one eye is gradually lessened by small fraction in each step until the maximum visual acuity is just reached.

6)The first lens is not removed until the next is in position to prevent reactivation of his accommodation . 7) The test is repeated in the other eye . 8)The entire examination must be slow and leisurely مُتَأَنٍّ ; مُتَرَاخٍ and the patient is given the strongest hypermetropic lens or the weakest myopic lens with which the best visual acuity is attained .

ASTIGMATIC FAN * On looking at such fan if any of the lines
* It is used to verify the axis of trial cylinder lens. * On looking at such fan if any of the lines are seen more clearly than the others astigmatism must be present . If the vertical line is clear more than the horizontal meridian it is the less emmetropic one (has the defect). (Inverse relation). more clear line = less emmetropic . Less clear line = more emmetropic

ASTIGMATIC FAN A cylinder lens is placed in front of the eye with its axis horizontal will correct the vertical meridian and when the correct glass power is to be worn all the lines of the astigmatic fan appear equally distinct. The cylinder which thus renders the outline المظهرof the whole lines equally clear is the amount of astigmatism and the axis of the cylinder is at right angle to the line which was initially seen most clearly (less emmetropic) according to the sign of the cylinder lens.

STAENOPIC SLIT 1) It is essentially an accessory in the trial set that
consists of an elongated pin hole aperture as a slit cut in an opaque disc , used to detect the axis of astigmatism if present. 2) When put before the eye it allows only rays of light in a particular meridian to enter the eye . 3)If the slit is placed horizontal before the eye the vertical meridian is pin holed and produces a point image. 4) After correction of any spherical ammetropia all meridians in 360 degree can be seen equally on rotating the staenopic slit.

STAENOPIC SLIT 5) In presence of a high astigmatism and before correction , the staenopic slit can detect the axis of correcting cylinder if it's properly positioned . 6) The slit is sometime useful in determining the astigmatism when other devices are unsatisfactory.

STAENOPIC SLIT 7) When the image is equally clear in 360 degree in presence of the slit no astigmatism is present , all lines are equally clear. N.B. Unlike the astigmatic fan , the slit of this device detect the less ametropic or the emmetropic meridian and the axis of the correcting cylinder lens is put on this meridian ( at zero power ).

CROSS CYLINDER LENS Jackson's cross cylinder (JCC) 1) It's a manoeuvre for ascertaining the strength and axis of the cylinder . 2) It's a mixed cylindrical combination of various strength in which the spherical component is one 1/2 of the (opposite) power of the cylindrical component with the axes at right angles. 3) The most convenient (comfortable; useful ) form is the combination of 0.25Ds and 0.50Dc.

1- Check the strength of trial cylinder
We apply the cross cylinder lens first in the same trial cylinder axis then perpendicular to it. In the first position we add say 0.25 D. to the power of the trial cylinder, but in the second we decrease 0.25 D. from the power of the trial cylinder .

DUANE When the correct cylinder axis has been found, attention is turned to determining the proper cylinder power. The cross cylinder is placed in front of the correcting cylinder with either axis (plus or minus) parallel to and superimposed on the axis of the correcting cylinder.

DUANE The plus and minus axes of the instrument successively come to overlie the axis of the correcting cylinder. Cylinder power is changed according to the patient's selection. For example, if the plus axis overlying the correcting cylinder axis produces the clearer image, more plus cylinder or less minus cylinder is placed in the trial frame. This is continued until equal clarity (or equal blurredness) is noted on twirling the cross cylinder.

Check the strength of trial cylinder
Result:- a) If no improvement of visual acuity occurs the trial cylinder is correct. b) If the first position of cross makes improvement we add 0.25 or move to the power of the trial cylinder. c) If improvement occurs in the second position we deduce 0.25 from the trial cylinder.

CROSS CYLINDER LENS 2- Check the axis of trial cylinder:-
To check the axis of the trial cylinder we apply a moderately strong cross cylinder obliquely in front of trial cylinder, so that each axis lies 45 degree to either side of the axis of the trial cylinder ,this is easily done as the Jackson's cross cylinder (JCC) is always constructed so as its handle is at 45 degrees to its major and minor cylindrical axes.

DUANE The term twirl means a “flipping” of the lens before the eye in such a way that the side of the cross cylinder facing the patient at the beginning of the maneuver comes to face the examiner at the conclusion of the maneuver. The term rotate refers to a clockwise or counterclockwise motion of the cross cylinder in front of the patient, in the plane of the spectacle lens, about an axis parallel to the line of sight.

DUANE The term correcting cylinder refers to the cylindric lens in the trial frame. The cross cylinder is now placed in front of the correcting cylinder, with its handle parallel to the axis of the correcting cylinder. In this position, the axes of the cross cylinder straddle the axis of the correcting cylinder at 45° each. It is explained to the patient that both images to be presented may be slightly blurred, but one may be clearer than the other.

DUANE The patient is to state which position of the cross cylinder presents the clearer image (position 1 or position 2) or whether they appear alike. The clearer image is the one that is sharper, darker, or more legible. The end point of the test is reached when no difference can be discerned between the two positions of the cross cylinder.

DUANE The cross cylinder is then twirled in front of the correcting cylinder. This maneuver reverses the positions of the plus and minus axes of the cross cylinder. If both positions appear equally clear (or equally blurred), then the axis of the correcting cylinder is at the proper meridian and the test for axis is complete.

DUANE If one position is clearer, the correcting cylinder is rotated toward the axis on the cross cylinder having the same sign as that of the correcting cylinder.

Jackson's cross cylinder (JCC)
The examiner simply holds it in front of the trial frame with its handle in the axis of the cylinder already used ,testing first with one face and then twirling (rotate rapidly ) it through 180 degrees to assess the other position. If visual improvement is attained by one or other alternative , the correcting cylinder is turned slightly in the direction of the axis of….

Jackson's cross cylinder (JCC)
..the cylinder of the same ( sign) denomination النوعin the cross cylinder . The test is then repeated several times until the position of the axis of trial cylinder is found at which rotation of the cross cylinder gives no (Change) alteration of distinctness .

1) In the verification of distant correction a high degree of accuracy may be obtained by making of chromatic aberrations. 2)The blue rays that have relatively short wave length were refracted more acutely and brought to a focus in front the retina sooner than the longer red rays. The red rays that have relatively long wave length were refracted less acutely and brought to a focus behind the retina. DUOCHROME TEST

Typical wavelength of colors VIBGYOR
Wavelength/ nanometer Color 410 Violet 450 Indigo 550 Blue 570 Green 580 Yellow 610 Orange 660 Red

DUOCHROME TEST 3) If the eye corrected, so that it's exactly emmetropic , a focus is formed between these 2 extremities (blue and red ) and the eye sees all the colours equally. 4) If the eye is myopic the red colour is seen more distinct, because it is nearer to retina.

DUOCHROME TEST

DUOCHROME TEST 5) If the eye is hypermetropic the blue is seen more distinct because it is nearer to retina. 6) Over corrected myopic eye (artificial hypermetropia) can see the blue or green more distinct and is in need for less minus lenses. 7) Under corrected hypermetropic eye can see green or blue colour more distinct , and it is in need for more plus lenses.

DUOCHROME TEST 8) Under corrected myopic eye can see red colour more distinct , and it is in need for more minus lenses to be emmetrope. 9) Over corrected hypermetropic (artificial myopia ) eye can see the red colour more distinct and is in need for less plus lenses.

THE DETERMINATION OF SPECTACLE FOR NEAR WORK17/3
1) We have seen that accommodation varies with age . 2) To obtain comfortable reading correction a certain amount of accommodation power must be kept in reserve. الاحتياط 3) Special lenses are needed for near work wherein near point recedes تتباعدand plus lenses act to bring the near point within the standard reading distance (30-40)cm. .

THE DETERMINATION OF SPECTACLE FOR NEAR WORK
4)The patient given the reading test chart (Jaeger types) and asked to hold them at distance that he accustomed to read at , while the distance correction after subjective refraction in the trial frame (not removed). 5) When the reading types are not distinct we add suitable convex lens to bring the near point within the working distance .

6) If history appears that the case is one of simple presbyopia the patient is asked to read the reading types first with his distance correction and after that gradually increasing power convex lenses are added until the standard vision is obtained allowing the patient to carry out his tasks he requires at the usual working distance (30-40 cm).

Accommodation (Difficult reading)

(ask your patient to read more and more to detect his eye strain )
THE DETERMINATION OF SPECTACLE FOR NEAR WORK 7) When particular reading difficulties seem to be the complain in subjects whose accommodation might be expected to be undiminished by presbyopia ( relatively young age) , the more extensive near vision on examination should be preferred. (ask your patient to read more and more to detect his eye strain )

8) Presbyopic correction should never be prescribed mechanically by ordering an approximate addition varying with the age ,but the patient should be examined individually, as the variation in refraction is wide, and the lenses prescribed for reading should be the most serviceable and comfortable , not necessarily the clearest vision for the particular work for which the lenses are intended.

9) In all cases it is better to under correct than to over correct presbyopia , since if the lenses described are too strong , difficulties will arise with convergence (weak convergence )and the range of near vision will be limited.

10) In all cases a lens which brings the near point closer than 28cm is rarely tolerated (that is , a total power of 3.5 D) and for any reason the demands of the work require a higher near correction it is usually wise to aid the convergence with prisms as well as the accommodation with spheres.

11) If near work with reading spectacles is still giving rise to troubles this is a situation in which the relative accommodation and convergence for reading must be estimated.

12) If the patient is working out side the area of comfort of his convergence orthoptic exercises should be described , or prismatic correction should be ordered to bring the convergence within normal.

13) Presbyopia is one of these conditions wherein glasses may be of real service in every day life like out shopping, looking at tickets or to time table, the patient is better to use a pair of bifocal lenses to save time with little annoyance.

THE DETERMINATION OF THE
MUSCLE BALANCE * It usually consists of three basic examinations:- A) The inspection of corneal reflections - The corneal reflection is inspected as the patient looks directly at a light held by the examiner's hand immediately infront of the patient.

MUSCLE BALANCE - The pin point images are called the corneal light reflex seen in both corneas. - These reflections are compared with respect to their position in relation to the center of the cornea and pupil. - Normally the pin points lie in the centers of the corneas as well as the centers of the pupils.

corneal light reflex o o o o Abnormal

Left Esotropia 15 degree L.E R.E

Left Esotropia 20 to 25degrees

40 degrees / Exotropia Left Eye

B) The cover test - This test is carried out on the basis of the inspection of corneal reflection. - If the latter suggests that one eye, says left eye is deviating , the patient is asked to continue his fixation in my light or in any near or distant object and the right eye is covered by a card or by examiner's hand , then:-

The cover test

The cover test If on covering the right eye the left eye moves to take fixation it surely has (a manifest squint( squint = strabismus. If on removing the cover the left eye remains fixating and the right eye stays in the deviated position the patient has an (alternating manifest squint). c) If however , on removing the cover the left eye is not fixating the patient has( a uniocular left manifest squint ) and the left eye may be lazy. d) If on covering any eye the other doesn't deviate a manifest squint is absent.

1)Before the cover R L STRAIGHT DEVIATED

2) After the cover Straight R.E

Cover test – Alternating Esotropia
R.E L.E Esotropic eye Left eye fixating Right eye fixating

To detect latent squint by cover test
- The same test is repeated but the behavior of the covered eye is observed. - If the covered eye is seen deviated while covering and returns to its fixating position on removing the cover , while the uncovered eye keeps its fixation position the patient has a latent squint.

To detect latent squint by cover test

Abnormal cover uncover test

* Pseudo squint: Due to wide epicanthal folds gives a false impression of esotropia (common in children 1-3 year) ,with age this false deviation disappears gradually.

C) The examination of ocular movements:: This test is very important in differentiation between concomitant and paralytic squint. - The eye movement should be examined in the all principle positions of gaze and cover test may be done in any position

* The patients are divided into 2 groups:-
MUSCLE BALANCE * The patients are divided into 2 groups:- 1- Those that have Binocular Single Vision (B.S.V.). In this group cover tests are done to discover the presence of any latent squint. 2- Those in which binocular single vision is absent. In this group the other tests are done for the manifest squint regarding of nature and amount.

MUSCLE BALANCE D) Cover-Uncover Test (unilateral)
The first step in this technique is known as the unilateral, or "Cover-Uncover Test. In this step, the goal is ONLY to differentiate between a heterophoria and a heterotropia, and, in the case of heterotropia, determine if it is unilateral or alternating. You cover and then uncover one eye at a time, and carefully observe the eye NOT being occluded (Uncovered Eye) on BOTH the cover and the uncover stroke. (position)

MUSCLE BALANCE Cover-Uncover Test
So, for example, the right eye is covered while the left uncovered eye is observed for any movement. If the left uncovered eye moves when the right eye is covered, it means the left eye was not fixating on the target before the cover stroke, and the patient left eye has a heterotropia (manifest strabismus.(Esotropia or exotropia.

Cover-Uncover Test

Next, uncover the right eye, while again observing the left eye for movement. If the left eye moves on the uncover stroke, it means the left eye was fixating while the right eye was covered, and the right eye returns to fixation when it is uncovered. This also indicates a heterotropia, specifically a unilateral heterotropia in the left eye . If the left eye does not move on the uncover stroke (keeps fixation), this is most likely an alternating heterotropia.

Cover-Uncover Test

This procedure is now repeated while covering and uncovering the left eye and observing the right eye. Each of these sequences may be repeated several times to confirm the results. The cover stroke should allow sufficient time (2 or 3 seconds) for the patient to have the opportunity to fixate with the uncovered eye.

Alternate tropia

Cover-Uncover Test Any loss of movement or complaint of diplopia should be recorded. Of particular importance is the examination of convergence, the accommodation and convergence have a close interrelation and weakness of any of them will result in absolute or relative weakness of the other .

E) Alternating cover test
In which each eye is covered in turn and the behavior of an uncovered eye is noted , and finally both eyes are uncovered , if no any squint is detected the eyes are normal (orthophoria is present).

ORTHOPHORIA No deviation in any eye

Alternating Heterophoria

Phoria

MUSCLE BALANCE Alternating Cover Test
The next two steps of this technique occur during the alternating phase of the Cover Test. The first of these steps is to determine the direction of the deviation (hypo/hyper, exo/eso). You alternately cover the right and left eyes while the patient views a distance or a near target, and observe the eye when the occluder is removed. If the eye moves outward (temporally), it means the deviation is esotropia

MUSCLE BALANCE Alternating Cover Test
If the eye moves inward (nasally), it means the deviation is exotropia. If the eye moves up, it mean the deviation is hypotropia. If the eye moves down, it means the deviation is hypertropia. If the deviation has been identified as a strabismus in Step 1 above, then deviation must be identified as either a hyper or hypo (unlike a heterophoria) depending upon the deviating eye.

Alternating Cover Test
For example, if the left eye is the deviating eye, and it moves upwards when it is uncovered, the deviation is a left hypotropia, which is NOT the same as a right hypertrophied . The final step is to determine the magnitude of the deviation, again using the Alternating phase of the Cover Test.

MUSCLE BALANCE With experience, you should be able to estimate the angle fairly (clearly ) well. But, it is always a good idea to prism neutralize the angle. With the right eye occluded, place a prism with the proper base direction (determined in Step 2 - base in for exo, base out for eso, base up for hypo, and base down for hyper), of an approximately correct power, between the occluder and the right eye.

N.B: Always put the apex of the prism toward the direction of eye deviation

Accommodation 1) Definition:- It is the ability of the crystalline lens to change its shape( the converging power) to focus objects of any distance up on the retina. 2) Mechanism of accommodation:- 1- The feature of accommodation is an increase of curvature of the eye lens mainly in the anterior surface. 2- It can be shown that in the state of rest the radius of anterior surface of the crystalline lens is 10 mm.

Accommodation 3- Hemholtz considered that the eye lens was elastic and that in normal state of rest it was kept stretched and flattened by the tension of zonule. 4- In the act of accommodation the contraction of ciliary muscle decreases the circle formed by the ciliary processes and the relaxed zonule , relieve the strain to which the lens was subjected , thus the lens assumes a more spherical form , the lens in accommodation increases in thickness and decreases in diameter showing a forward protrusion of the center of its anterior surface and a relative flattening of its periphery.

5- There is much interplay التفاعلof force between the lens capsule and lens substance (cortex + nucleus) . 6- The lens substance forms a passive plastic substance ,while the lens capsule forms the active modulus of the lens. 7- If the lens capsule was removed , the lens substance assumes a more unaccommodate flat shape.

Accommodation 8- In presbyopia a natural decrease of accommodation occurs with age , here there is a progressive weakness of the capsule's ability to change the shape of the lens substance from the unaccommodated shape to accommodated shape.

Accommodation

Unaccommodating Eye Accommodating Eye

* Three aging factors of accommodation in presbyopia:-
1- Decrease in the elastic modulus قالبof the lens capsule. 2-Increase in the lens substance (size + density ). 3- Flattening of the lens as whole.

PHYSICAL AND PHYSIOLOGICAL ACCOMMODATION
1- Two factors enter into the efficiency of accommodation:- a- The ability of the lens to change its shape (physical accommodation). b- The power of the ciliary muscle (physiological accommodation). 2- If the substance of the lens becomes inelastic, as it occurs in progressive age , so that it can no longer change its shape , accommodation can not act even if the ciliary muscle violently contracts.

ACCOMMODATION 3- On the other hand a weak or paralysis of the ciliary muscle will not be able to induce change in lens shape even in children.

PHYSICAL ACCOMMODATION
It's an expression of the actual physical deformation of the lens, and it's measured in diopters , thus if the converging power of the eye lens increases by one diopter we speak of the expenditureالانفاق of one diopter of the accommodation.

PHYSIOLOGICAL ACCOMMODATION
- It's the action of ciliary muscle and is measured by the unit myodiopter which equals to the magnitude of ciliary muscle contraction to raise the refractive power of the lens by 1 diopter. - Both physical and physiological accommodation correspond each other during the first 1/2 of life.

PHYSICAL AND PHYSIOLOGICAL ACCOMMODATION
- But during the second half of life (after age of 40) both types of accommodation dissociate ( separate ) where the physical accommodation fails to cover the needs of near work while the ciliary muscle is still intact and powerful but the lens becomes hard this occurs in presbyopia .

ACCOMMODATION - Conversely a failure of the physiological power of ciliary muscle may appear in states of debility like in famines and in diseases of the parasympathetic nerve supply ( as in oculomotor lesions ) to that muscle when the muscle fails at any age , while the lens is intact. - Since an attempt of ciliary muscle to cover the accommodation deficiency (weakness) by a sustained and exaggerated contraction( which always ends in ciliary muscle fatigue )such a weakness may be responsible for eye strain and asthenopia.

THE RANGE (Distance) OF ACCOMMODATION26/3
1- The furthest point away at which the eye can see an object clearly is called far point (pointum remotum) The nearest point at which the eye can see an object clearly is called near point (pointum proximum) . 3- The distance between far point and near point is the range of accommodation.

THE RANGE (Distance) OF ACCOMMODATION
( a=r -p ) a: range of accommodation. r: is the distance of far point (accommodation is relaxed , lens is flat). p: is the distance of near point ( eye is fully accommodated , lens is thick) . In emmetropia. (r = ∞, p =10 cm) ( a = ∞- 10 = ∞ ) N.P R F.P r p Retina a

Amplitude (power) of accommodation
4- (A=P-R) A: is the amplitude (power) of accommodation P: is the refractive power of accommodation at near point . R: is the refractive power of accommodation at far point.

AMPLITUDE OF ACCOMMODATION in different refractive errors
1-In emmetropia. (r=∞, p=10 cm) ( a=∞- 10 =∞ ) (P= 1/0.1=10D , R=1/ ∞ =0) (A=10 – 0= 10D) 2- In hypermetropia , to see clearly at a distance he has to exert an amount of accommodation equivalent to the amount of emmetropia , but to see an object at 10cm (near) he must add an amount of 10D to put his eye accommodation on an equality with the emmetrope. In hypermetropia his near point =20cm. Although this range of accommodation is the same (∞- 10 =∞ ) , his amplitude of accommodation is necessarily greater than emmetrope (10+10=20D)

Age /Years Amplitude of accommodation in Ds 8 14 12 13 16 20 11 24 10 28 9 32 36 7 40 6

AMPLETUDE OF ACCOMMODATION
44 4.5 48 3 52 2.5 56 2 60 1.5 64 1 68 0.50 70

3- A myope has far point at finite (<6 ms) distance.
Suppose that myopic person can see distant objects distinctly at 100 cm., his refractive error could be corrected by a concave lenses = - 1 Ds. to see like emmetrope. let us suppose that his near point =10cm=1/10 meter, P=10 D ,R =1 D A=P-R= 10-1=9Ds.

THE RANGE AND AMPLETUDE OF ACCOMMODATION
- A myope , although he cant not see distant object clearly, has the advantage he can see near object , with less effort and sustainly than each of emmetrope and hypermetrope.

4- In astigmatism there is no evidence of accommodative effort acting unequally in order to correct an astigmatic error , and so it follows that a distinct image is never obtained in astigmatism, but the focus is a circle of least confusion..

5-In anisometropia, since the accommodative effort of the 2 eyes can not be dissociated the error of an anisometrope can not be corrected by his accommodation so as when correcting lenses are not used ,the image of one eye ( more ametropic eye) is always blurred.

FATIGUE OF ACCOMMODATION
1- The fatigability of accommodation must be easily measured by the technique initiated by Lucien that had studied the fatigue in skeletal muscles. 2- Briefly, it consists of repeated approximating to the eye a target carrying as object a dot or small letter until it becomes blurred.

3- There should be no evidence of diminution of excursionاِنْحِرَاف ; حَيْد in 15 minutes , whereafter the factor of general fatigue may become obvious. 4- It was noted that the response of the 2 eyes to the test may be different (one eye suffers fatigue before the other).

5- On the whole , in the normal eye it is difficult to fatigue the accommodation and in a considerable proportion of cases its excessive use in near work may lead to development of a greater amplitude. 6- If, however , visual tasks are continued at a range near to the near point of long time, fatigue appears even in a normal emmetropic and orthophoric eye .

7- Therefore the near point gradually recedes with age , example at age 36 years , near point reaches 14 cm, when his amplitude of accommodation becomes only 7Ds , instead of 14Ds at 8 years . 8- At the age of 45 years near point reaches 25 cm and accommodation becomes only 4Ds, at the age of 60 years near point reaches to 66.6 cm while accommodation becomes only 1.5Ds.

Accommodation

9- In the majority of cases near work is done at average distance (28-30cm) away from the eye before presbyopia. 10- At 45 years clear vision needs to be at (40-50cm) with accommodation only (3.5-4Ds) and near point recedes to 22cm they said that presbyopia has set in.قصو النظر قد حل

In this individual , if he tries to read without correction for long time at 30cm he needs to use of all his accommodation and eye strain is the result , without tolerationاِحْتِمَال ; اِسْتِطَاعَة too much near work. 11- Comfort demands , that 1/3 of accommodation must be kept in reserve .

12- In emmetropes, presbyopia occurs between 40 and 45 years , although there is geographical variation as in tropics where presbyopia sets in relatively early, and accommodation must be supplemented with convex lens for clear and comfortable reading.

13- A hypermetrope starts his life with near point considerably further away from the eyes , so that presbyopia occurs earlier than in emmetropes. - Thus , a hypermetrope with +3.00D correction for distance vision must use addition of convex lenses for reading suitable for his near refraction irrespective of age.

14-In myopes , where the opposite conditions hold (near point is closer to eyes than normal) and if a myope has a refractive error of -4.00D , presbyopia will never occur (late presbyopia).

15- Presbyopia is thus a relative term depending on :-
Age . Refractive state. Habits. Type of near work. Weather. Presbyopia occurs earlier on hot weather than cold weather.

16- A person who has the habit of reading with his book on his knees complains of presbyopia later than one who is used to read more closely, and carpenter or book keeper or the musician will be comfortable when works at 30-35cm or over.

17-While the seamstressخَيَّاطَة or the compositorمنضد حروف الطباعة or the engraver نَقَّاش of the same age is forced to use glasses for near work at 20cm. 18- There is thus no fixed presbyopic point , thus there is no fixed rational صِيغة role of treatment .(It forms an individual condition)

SYMPTOMS OF FAILURE OF ACCOMMODATION
The ciliary muscle may fail in state of debility like in famines or in some diseases with fever lead to failure of physiological accommodation having the following symptoms:- 1- Small print becomes indistinct. 2- Near point recedes and the patient tends to hold his head backward and his book forwards until the distance in between is reached when clear vision in any circumstances is difficult. 3- Troubles are experienced at first in the evening when the light is dim and the pupils are dilated , permitting diffusion circles to develop.

4- Difficulties arise easily after a long day of fatigue. 5- Presbyope likes , to read in a brilliant (shining) illumination and he tries to get the light between his eyes and the book or to read in sunlight to make the pupils to constrict. 6-In senility when the pupils become small and old person without accommodation may see near objects with fair (comfortable )degree of detail.

7- Uncorrected early presbyopia (like in hypermetropia) may be marked by ciliary muscle spasm which produces temporary blurring of distance vision like artificial myopia. 8- Failure of accommodation leads to eye strain with effort. SYMPTOMS OF FAILURE OF ACCOMMODATION 31/3

9- The eye strain will result in :- a) Headaches . b) Tiredness of eyes. c) Redness and burning of eye with excessive tearing on effort . d) inability to do more useful near work.

Treatment of presbyopia
1- The treatment of presbyopia is to:- Provide the patient with suitable convex lens for near work to bring his near point within the normal reading distance (30 – 40 cm). 2- To do this we must:- a) Know his near point . b) Do a good refraction for distance. c) To determine his amplitude of accommodation (Pn – Pf). .

3- When you prescribe the near correction don't forget to keep 1/3 of his eye’s accommodation in reserve. 4- If the patient is emmetropic presbyope and wishes to read at 25cm he will require (1 0.25= 4D) but his near point 50cm, thus his accommodation is 2D to read at 25cm, he needs an addition of another 2Ds.

but we must keep 1/3 of the 2Ds. in reserve which equals 0.7D thus his amplitude is 1.3 Ds and it needs add of 2.7 DS. 5- If the patient has ammetropia we determine his distant correction and his near point to render him emmetrope , then we add the suitable near correction according the same rule.

6- It's true that presbyopic correction should never prescribed mechanically (blindly) giving the patient convex lenses according to his age , but each patient should be tested individually and the lenses should be ordered in each case which give the most serviceable and comfortable vision and not necessary the clearest vision.

7- In all cases it's better to under correct than to over correct , since the too strong lenses will result in difficulties regarding the (AC/A) (accommodative convergence / accommodation ) ratio, also the visual field will become limited .

8- To prevent over correction it's better to prescribe the lenses for reading that enable the patient to read clearly (12-15 cm) further away from the normal reading distance (30-40 cm). 9- The average subject's accommodation declines, so that during age of sixties addition of +2.50D for reading becomes necessary according to the refractive state of the elderly , and thereafter a little further addition is required.

10- In any case an added lens which brings the near point closer than 28cm is rarely tolerated. 11- A very strong additions for near work are often indicated in the presence medical eye diseases like age related macular degeneration (ARMD) and cataract as visual aids.

12- Patients with early cataract will often be enabled to read more comfortably using (+3.50 to D) addition . 13-Even higher additions may be considered as visual aids in rehabilitation of the visually handicapped persons.

INCREASED ACCOMMODATION
A) Excessive accommodation I)- Certain degree of sustained increased accommodation is not infrequently found in:- 1- Young hyperopes which considered as a physiological adaptation of ciliary muscle in interest of clear vision .

2- In myopes especially in young subjects doing much near work. 3- In astigmatic errors doing much work. 4- In excessive convergence. 5- In all patients trying to gain clear near vision in spite of refractive errors.

II)- It is also seen most frequently in young people but it's not unknown in middle age when presbyopia is beginning to become apparent in which the accommodation is being strained by an amount of near work which is accomplished only with difficulty .

III) A large amount of near work is an important factor in the causation of accommodative strain especially when:- 1-work is habitually undertaken in deficient or excessive illumination.

2- Also the presence of uncorrected refractive error. 3-Or the wearing of improper or ill-fitting spectacles are other causes of excessive accommodation. 4- Otøer causes are general debility and ill health either physical or mental.

Symptoms and signs of excessive accommodation (Clinical pictures):-
1- The condition involves production of artificial myopia which varies from time to time according to the amount of near work , at rest the refraction is hypermetropia but after strain by near work it's myopia and more and more myope with more effort. 2- Both far point (F.P.) and near point (N.P.) become closer to the eye 3-Distant vision becomes blurry. Distant vision is therefore can be improved by concave lens.

Clinical pictures Of INCREASED ACCOMMODATION
4- In more marked degree the near work also becomes blurry with confusion of printed pages which is relieved by temporary rest. 5- There are typical symptoms of accommodative asthenopia including headaches, feeling of fatigue and discomfort in the eyes themselves.

6- Normally after the instillation of atropine drops in the patient's eyes to abolish the action of the ciliary muscle the refraction becomes hypermetropic by 1D , the diagnosis is proved by finding a great difference between the precycloplegic and postcycloplegic refraction. 7- The prognosis of such cases is good and the treatment is effective after prescription of postcycloplegic correction.

* Treatment of excessive accommodation:-
1- The affected eyes may be kept under atropine cycloplegia for (1-2 weeks) in order to ensure absolute rest of ciliary muscle , to allow the over excited ciliary muscle to recover from the condition of irritability. 2- The general treatment is more important than eye treatment .

3- Near work should be forbidden for a period of time . 4- A holiday with a change of air usually has a good beneficial effect. 5- A good postcycloplegic optical correction. 6- Control of near work for another period of time .

B) Spasm of accommodation
1- Causes:- a- Continuous sever near work in presence of refractive errors. b - Miotics such as eserine or pilocarpine eye drops may bring spasm of ciliary muscle. 2- Precipitating factors:- a- Marked degree of muscular imbalance (phoria or tropia). b- Trigeminal neuralgia. c- Dental lesion. d- General intoxication. e- Cases of iridocyclitis.

Spasm of accommodation
3- The ciliary spasm usually out of the patient's control (involuntary) and its amount may reach 10Ds or more that leads to marked artificial myopia. 4-Symptoms:- a- A blurring of near and distant vision . b- The patient is neurotic and drowsy. c- All symptoms of accommodative strain in excess (exaggerated).

Spasm of accommodation
5- Treatment of ciliary spasm:- A- Complete paralysis of ciliary muscle using atropine drops for (2 – 4 weeks) or more ,which may be repeated if any spasm still has any effect. B- Correcting spectacles must be used for any near work according to refraction after recovery of the muscle. C- The general health and habits of the patient should be closely supervised.

DIMINISHED ACCOMMODATION
A) Insufficiency of accommodation:- 1- In this condition the accommodation power is constantly below the lower limit of what may be accepted as the normal variation of patient's age. 2- It's a relatively common condition may be caused by one of the following factors:- a) The failure of accommodation may be lenticular in origin arising from sclerosis of the lens , which is common in premature presbyopia and affects the physical accommodation only. b) Weakness of the ciliary muscle leads to failure of physiological accommodation as in physical or mental debility.

3) The etiology of such case in (b) includes all the causes of muscle fatigue like:-
a) Debility – Anaemia - Malnutrition. b) Excessive near work in unfavorable conditions. c) Failure of ciliary muscle may also occur in prodromal stage of chronic simple glaucoma.

4) Symptoms include all the features of muscle fatigue like:- a) Headaches, asthenopia, eye pain, drowsiness. b) Near work is blurred and becomes difficult or impossible. c) Some time, an attempt to read clearly may lead to excessive convergence. 5) The duration of accommodation failure depends on the presence of the causes.

6) Treatment:- a) Correction of any refractive error . b) Providing the patient with gradually increasing convex lenses for near work. c) In presence of excessive convergence a suitable prism is used in the spectacle. d) In all cases the weak convex lens is used at the start for near work to stimulate the weak accommodation.

f) During the exercise the patient must wear his near correction. g) The convex lens for reading decreases gradually according to the increase in the magnitude of accommodation till the patient can read without glasses. h) Any malnutrition or anaemia must be treated. i) Regulation of near work j) Improvement of general health and exercise.

B) Paralysis of accommodation:-
I) Causes : a- General causes 1- Drugs like :- - Antihypertensive drugs. (drugs which counteract high blood pressure ) - Antidepressant drugs. (medication used to relieve depression). - Antispasmodic drugs.( drug which reduces spasms or cramps) . 2- Any disease or trauma that affects the midbrain or the course of parasympathetic nerve supply to ciliary muscle.

Paralysis of accommodation
3- Central neurological causes:- - Vascular disorders. الاوعية الدموية اضطراب - Cerebral syphilitic infection. سِفْلِسيّ Hysteria. الهستيريا . الهَرَع Encephalitis. التهاب الدماغ

4- Infectious diseases like:-
- Mumps. النُّكاف - Tonsillitis. التهاب اللوزتين - Pneumonia . اِلْتِهابٌ رِئَوِيّ Herpes zoster. الفَيْروسُ الحزام الناري 5- Non infectious toxic states:- - Belladonna intoxication. بست الحسن التسمم - Chronic alcoholism. إِدْمانٌ على الكُحُول - Certain cases of diabetes mellitus (D.M.).

b- Local causes:- Paralysis of accommodation:
1- Short acting cycloplegic drops cyclopantolate. 2- Long acting cycloplegic drops atropine. 3- Eye trauma affecting the ciliary body.

PARALYSIS OF ACCOMMODATION
Symptoms and signs:- 1- Receding of near point so as the far point and near point becomes close together. 2- Impossible near work. 3- Distance vision is not affected. 4- Full dilatation of the pupil, if the sphincter pupillae is affected leads to marked dazzleانبهار 5-Micropsia رُؤْيَةٌ مُسْتَصْغِرَة which is reverse of macropsia in accommodation spasm .

Paralysis of accommodation
III) Treatment depends on the cause:- 1- In paralysis of central nervous system (C.N.S.) the prognosis is bad (no actual treatment). 2- In encephalitis the condition may be transient or prolonged. 3- In toxic condition the prognosis may be good. 4- In head trauma and eye trauma follow upالمتابعة is the rule . 5- The eye must put in rest without any near work . 6- In cases which are hopless of the accommodation to recover the patient is supplied by high plus lenses as a type of visual aid.

Changes in refraction A-Physiological changes
To a large extent these changes may be erratic شارد ، ضال , but there certain well defined tendencies of general occurrence which may be considered physiological .

Changes in refraction The change from HM at birth to emmetropia as growth proceeds , a change which may progress to the development of myopia . The apparent increase of HM which accompanies advancing years and which indicates a decrease in the power of accommodation and an absolute increase in the HM with age as in presbyopia ,

Changes in refraction which results of changes in the size and refractivity of the lens In astigmatism also there is frequently a tendency to gradual change .

Decrease in the power of accommodation with age
Age /Years Amplitude of accommodation in Ds 8 14 12 13 16 20 11 24 10 28 9 32 36 7 40 6

Decrease in the power of accommodation with age
44 4.5 48 3 52 2.5 56 2 60 1.5 64 1 68 0.50 70

Changes in refraction B- Pathological changes
1- The first of these are changes in the dynamic refraction due to conditions of spasm or paralysis of ciliary muscle. The effect is typically seen in the one diopter of HM which is revealed by the ciliary paralysis following the instillation of atropine drops in the eye.

B- Pathological changes
The same effect is seen in those neurological disorders which similarly affect the ciliary muscle (paralysis) ,like paralysis of oculomotor nerve. 2- Trauma to the eyeball may act in the same way , and many cases of transient refractive changes have been reported as a result of an accident involving an eye blow as paralysis of the ciliary muscle.

3- A crystalline lens displacement backwards or forwards will have the same optical effect , while a subluxation and tilting اِعْوِجاج ; اِلْتِوَاء of the lens will produce a marked degree of astigmatism .

Changes in refraction 4- The myopia which accompanies spasm of the ciliary muscle is sometimes met with in acute iritis , the spasm being due to the irritant effects of inflammatory products .

5- A transient myopia occurring in various toxic status such as jaundice and influenza and after drug administration such as arsenicals and sulphonamides is now well announced in the literature .

6-Chemical relatives of sulphonamides such as carbonic anhydrase inhibitors ( Diamox ) and the thiazides have been held responsible for transient myopia. - As a rule the myopia doesn’t occur when the drug is taken initially but during a subsequent period of dosage suggesting that a sensitivity develops .

Most writers ascribed the phenomenon to an irritative toxic spasm which may be due to a central toxic irritation of the parasympathetic nerves or centers . - It is interesting that as a rule the myopia varying from 1 – 4 D in degree and from a few days to a few weeks in duration , is frequently the only toxic symptom of drug induced myopia.

7- Slight refractive changes may occur in glaucoma . After operation any shallowness of the A.C. invariably produces a marked index myopia and the period following the operation to reestablish the normal chamber depth and the recessionانسحاب ،ارتداد، انحسار of the lens are accompanied by the gradual development of HM .

Changes in refraction - A much more significant happening in glaucoma is a loss of accommodation because of pressure on the c.m. (mechanical effect), and its occurrence is a sign of some diagnostic importance . - The accommodative loss may vary rapidly in states of temporarily raised tension in CAG so that the print in reading suddenly becomes blurred .

Changes in refraction While in simple glaucomas (OAG)
a permanent loss of A. may develop more rapidly than would normally be explained by the physiological development of presbyopic changes (early presbyopia).

8- When the coats of the eye are diseased refractive changes are produce more readily This is most obvious in corneal disease: a- Such as astigmatism usually results after a corneal deformity largely cicatricial in nature resulting in scar formation (leucoma). b- A softening of the cornea may result in a progressive keratoconus ( after keratomalacia).

Changes in refraction c- Scleritis has been recorded as producing a considerable degree of myopia . d- A choroiditis has been noted to cause a similar refractive error .

9- Refractive changes of considerable importance are associated with alterations in the refractivity of the lens . The most common of these is the gradual myopic change which accompanies the early changes of cataract .

It is the result of the increase in optical density of the lens which occurs in this disease (cataract) and is most evident when the nuclear portions are particularly involved (nuclear sclerosis).

Changes in refraction 10- In Diabetes Mellitus the most interesting and dramaticمثير changes occur , where the changes in refractivity come on suddenly and bilaterally , that a myopic trend is associated with a rise (hyperglycaemia) , and a hypermetropic with a fall (hypoglycemia) , in the sugar concentration of the blood ,

and that the hypermetropic trend seems not to occur as an initial phenomenon , but to follow a myopic change . If the blood sugar concentration varies clinically , the refractive state of the eye may follow , altering from hypermetropic to myopic and v.v.

Changes in refraction It is evident that these changes arise from events in the lens . It may be that the myopia associated with a rising sugar concentration is due to hydration of the cortical layers (decrease osmotic pressure) of the lens relative to the nucleus .

Changes in refraction In order to establish osmotic equilibrium, fluid tends to flow into the lens from the chambers of the eye . This tissue of the lens therefore swells and is deformed ,its curvature being increases further , the optical density of its peripheral layers (cortex) becomes diminished while the nucleus remains unaltered .

Changes in refraction In both counts its refractive power is increased and the eye becomes myopic -With fall of sugar concentration a reverse osmotic flow occurs and a condition of HM is produced , hydration of the nucleus of the lens being responsible for the hypermetropic change .

Clinical importance Whatever the cases of the changes a sudden and inexplainable myopia should always suggest the possibility of D.M. and direct attention to the urine , occurring in a known diabetic it should suggest an inadequate control of the disease . On the other hand , a sudden hypermetropic change , indicating , as it does , a general disturbance in the H2O balance of the body .

Changes in refraction In either case the Rx should be directed not to the eye but rather to the constitutional disease , for the refractive change is transitory and invariably returns to normal provided metabolic equilibrium can be reestablished . If spectacles are to be prescribed , they need be considered only as an emergency and temporary measure.

Changes in refraction 11- Finally pressure on the globe from outside may produce slight changes of refraction mechanically . An orbital tumour may bring about HM or hypermetropic astigmatism from axial pressure . An orbital inflammation has been noted to induce a similar transitory myopia .

Changes in refraction - Pressure by the finger or a tumour or swelling in the lids (large chalazion) may also involve a transient astigmatic changes . A similar change may follow a tonometry or advancement operation on the E.O muscles or a buckling procedure for RD .

" Voluntary and reflex convergence "
Convergence can be initiated in two ways voluntarily and involuntarily . 1- Voluntary convergence ( the volitional إراديّ rotation of the two eyes nasal wards ) is initiated in the frontal lobe of the cerebrumمقدم الدماغ . 2- Involuntary convergence , on the other hand , is a psycho – optical reflex centered , like accommodation in the peristriate area of the occipital cortex .

Convergence In normal circumstances convergence is a fusion movement carried out synergically with accommodation . Reflex convergence : When the eyes are at rest and looking in the distance , the visual axes are parallel and no effort of accommodation is made . In order to see something clearly near at hand , not only must the eyes accommodate , but the visual axes must also be turned inwards so that they are both directed upon the object of attention (target) .

Convergence If an object is gradually brought nearer to the eyes , they converge more and more upon it till ultimately a point less than 8 cms. from the eyes is reached. At this point the image appears double , and giving up يتخلى عن the sustained effort , the eyes usually diverge slightly outwards . Normally it should be possible to maintain convergence when the object is about 8 cm. away .

Convergence The nearest point for which convergence is possible is called the near point (punctum proximum) of convergence =8cm. The relative position of eyes when they are completely at rest is called the far point (punctum remotum ) of convergence . As a rule the visual and the optic axes do not coincide , but in the position of rest there is generally a slight deviation of the visual axes outwards .

Convergence The far point (punctum remotum ) of convergence , instead of being at infinity , is thus situated beyond infinity and corresponding to the far point of accommodation in the hypermetropic eye . On the other hand in those cases wherein there is an apparent convergence of the eye in the position of rest , the far point (punctum remotum ) of convergence will be situated at a finite distance as in myope.

Convergence The distance between the far point and the near point is called the range of convergence. The difference in converging power required to maintain the convergence of the eyes in each position is called the amplitude of convergence .

Convergence The part of the range of convergence between the eye and infinity is described as positive convergence. That part of the range beyond infinity and that is behind the eye is spoken of as negative convergence ,really it is a divergence.

The measurement of convergence
I-First method : a convenient مُتَوَافِق method for measuring convergence was proposed by Nagel , the unit of which is called the meter angle ( m.a.) Let us imagine that when the eyes are at rest the visual axes are directed slightly forwards in parallel lines ( Fig )

object 2m visual axes 1m Figure 17.1 1/2m

If they are converged upon an object situated 1 meter away on the median line between the two eyes , then the angle which the line joining the object to the centre of rotation of either eye makes with the median line is called one meter angle .

Convergence -The angular displacement will necessarily vary with the distance from person to person between the two eyes IPD. (direct proportion). -If the object is 2 meters away , the angle will be halved ( 0.5 m.a. ) , if it is brought nearer say to 0.5 meter, the angle will be doubled ( 2 m.a. ) inverse proportion .

Convergence - The normal amplitude of convergence may be taken to be meter angle (m.a) , which is made up of 9.5 m.a of positive and 1 m.a of negative convergence , but it may exceed this and equal 15 or 17 m.a .as in high hypermetropia.

object 2m 1m Figure 17.1 1/2m

Convergence It will be remembered that the amount of accommodation used by an emmetrope to see an object , one meter away is 1D. , so that the amount of accommodation expressed in Ds. is the same as the amount of convergence expressed in meter angles

Convergence II-A second method of measuring convergence is by means of prisms . If an adducting (base out )prism placed before one eye a prism with its base directed outwards , the rays of light entering the eye will be deviated outwards by an amount depending on the strength of the prism Fig and diplopia will tend to be produced . - Consequently , if binocular vision is to be maintained , the eye must be turned inwards by a corresponding amount .

Convergence 1 adducting prism 2 object Fig

Convergence The stronger the adducting prism through which B.S.V. (no diplopia ) can still be retained is therefore the measure of the power of positive convergence . - Conversely , if an abducting (base in ) prism be placed before the eye ( that is a prism with its base inwards ) , the rays of light will be converged inwards and , in order to compensate for this , the eye will have to be deviated outwards ( Fig ) .

Convergence object abducting prism 1 2 Fig

Convergence The strongest prism ( base in) which can be borne without producing diplopia is thus a measure of the negative convergence ( or divergence ) . In all of these cases the amount of convergence is shared equally between the two eyes, so that the effect is the same whether one prism is used before one eye or 2 prisms. Each of 1/2 the prism strength , are placed one before each eye .

Convergence The positive position of convergence is much larger than the negative , each varies with wide limits , but on average with prisms gradually applied , the former can amount to about 55 – 60 prism unit and the latter varies between 3 and 7 prism unit .

The relation between accommodation and convergence
- The two synkinetic functions of accommodation and convergence are normally closely inter-related so that accommodation in Ds. is numerically equals to convergence in meter angle ( 1 m.a = 3 prism diopters) - The relation between them , however is quite elastic , and either can be exercised separately .

For example , if we look at an object with both eyes , and then while still looking at it ,place weak concave or convex lenses in front of the eyes we can overcome the effect of the lenses by an effort of accommodation and still see the object binocularly , in this case we are making an effort of accommodation without employing اِشْتِغال convergence .

-Conversely , if we repeat the experiment this time placing prisms in front of the eyes , we can still see the object distinctly , thus demonstrating that convergence can be called upon without involving accommodation. -When accommodation fails in middle age , convergence is retained , and when the ciliary muscle is paralysed by atropine , convergence is still possible .

An emmetrope who wishes to look at an object 25 cm. away exercises 4 Ds of accommodation and 4 m.a. of convergence , to see it clearly. But a hypermetrope of 2D. must employ 6D. accommodation and 4 m.a. of convergence ,to see it clearly. A myope of 2D will require only 2D. of accommodation while the amount of convergence remains the same 4 m.a. . The hypermetrope , therefore has to use his accommodation in excess of his convergence. The myope has to use his convergence in excess of his accommodation.

The amount of dissociation which is possible is not , however , unlimited , convergence can be increased by practice and it varies with different individuals and in the same individual at different times . The amount of accommodation which is thus possible to exert while the convergence remains fixed is called the relative accommodation which can be divided into (+ ve PRA and – ve NRA), the amount in excess of convergence without increase in accommodation ( as in myopia) is called positive convergence and that (with increase in accommodation ) as in in hypermetropia is called negative convergence.

Convergence The relation between these will be made clear from figure 17.4 1- An emmetropic patient has F.P. at infinity and his N.P. at 10 cm, suppose he looks at an object (A) situated 33 cm away , he will then be exercising 3Ds. of accommodation and 3 m.a of convergence . Concave lenses are now placed in front of his eyes until the object begins to be blurred .

1d None figure 17.4 A3ds P- 6ds P 10ds

Convergence If this occurs with – 3.0D lens he has increased his accommodation from 3 to 6 Ds. and his relative N.P. (p.) is at a distance equivalent to 6D. that is 17 cm. away from the eye. Convex lenses are now substituted for the concave lenses and it is found that the image begins to be blurred when lenses of +2D. are presented . He has thus relaxed his accommodation by 2Ds. that is from 3 to 1 and his relative F.P.(R) is at a distance from the eye equivalent to 1D. that is 1 meter.

Convergence For 3 m.a. of convergence therefore , the relative F.P. is at one meter. the relative N.P. is at 17 cm , the relative range of accommodation is 83 cm ,of which 67 cm is negative and 16 cm positive and the relative amplitude is 5Ds. ( 6D – 1D ) of which 2D is negative and 3D. is positive . - It is obvious that the nearer the object is to the eye , the smaller will be the positive and the larger the negative range of accommodation .

In the ultimate, if the eyes are emmetropic when the object of fixation is at infinity, there will be no negative accommodation and it will be found that no convex lens can be tolerated and at the same time good vision obtained. Similarly, if the object ia at the N.P the positive moiety will have become nil, fore there no concave lens can be tolerated since it require all the accommodative effort possible to see an object at this distance.

Convergence 23/4 Accommodation is thus one of the most important factors which may stimulate convergence , this is termed accommodative convergence . - In practice , it is only necessary to measure the amount of relative accommodation usually 33 cm , that is with convergence 3 m.a. - The patient is first rendered emmetropic with lenses , and small type (chart) is held at this distance from the eye .

Convergence - Concave lenses are then put up until the strongest accommodation is found that enables him to see readily , this is the measure of the amount by which he can augment يزيدincrease his accommodation i.e. of the positive accommodation . - A similar procedure is carried out with convex lenses , this is a measure of the amount by which he can relax or decrease his accommodation i.e of the negative accommodation and the sum المجموعof the two gives the total relative accommodation .

The relation between accommodation and convergence that is the magnitude of the change in convergence in prism diopters caused by an increase in accommodation expressed in diopters ,the accommodative convergence /accommodation ratio (AC/A) ,is remarkably constant for each individual ,being about /D . It is ,however ,upset اضطراب if the tone of the ciliary muscle is changed as in cycloplegia or in presbyopia.

The clinical importance of the relationship
Is that it is essential for comfort, that the positive portion of the relative accommodation should be as large as possible .It should be at least as great as the negative portion of accommodation . When it is large , the patient has a correspondingly large amount of accommodation in reserve , but in the opposite case he will be working too near the limit of his capacity for comfort , for , like all other muscles.

Thus the ciliary muscle becomes fatigued if it is called upon to contract to its utmostالحدّ الأقصى for any length of time . In such circumstances 2/3 of accommodation could be made available , and that about 1/3 of the total accommodative power must be held in reserve . If for any reason the amplitude of accommodation is decreased , and the N.P. recedes to the region of the W.D. so that the positive accommodation becomes small as in presbyopia….

…….prolonged near work can be undertaken without distress only if convex lenses are provided which bring the range of accommodation nearer to the eye . In a similar manner , if the accommodation is kept constant the convergence may be made to vary . The amount of convergence which can thus be exerted or relaxed is called the relative convergence .

Binocular Accommodation
Not only are convergence and accommodation closely related , they also have a mutualتعاوني ، متبادل effect the one upon the other . This is most readily seen in the fact that when both eyes are being used the power of accommodation is notably increased , the increase being due to the stimulus which the act of convergence gives to its related function to accommodation .

- The excess of binocular over uniocular accommodation averages about 1/2 D. , although individual variations are large , and it may be as high as 1.5 D . Duane gave the following figures : - Below 17 years, excess averages 0.6 D 18 – 31 years, excess averages 0.5 D 32 – 53 years ,excess averages 0.4 D Above 53 years ,excess averages 0.3D

- It appears to be definitely established that this additional accommodative efficiency is due to the stimulus derived from convergence . It is not a result of the accompanying pupillary contraction ( miosis ) , for it occurs independently of this. Nor is it due to an increase in V.A. depending upon the fusion of the two images from both eyes ,for the increase in binocular accommodation is notable in patients in whom one eye is amblyopic.

Convergence and accommodation
The two functions are closely interwoven تَشَبَّكَ physiologically , and it appears that their maximum efficiency can be attained only if , by working with each other , their synkinetic action is retained .

Fatigue of convergence
This could be studied by using ophthalmic ergograph . By repeatedly approximating a target towards the eyes until a fine line appears double . The excursion زيغان attained and the length of time can be studied using ergograph of Berens so that records can be made of the rate of development of fatigue and the individual capacity or resistance to fatigue .

Convergence Anomalies
Convergence Excess A habitual excessive conv. Or even spasm of conv. is not very uncommon (High AC/A ratio may be greater than 6.00 Δ/D ) . Etiology: 1) The most clinical picture is the increase of convergence that is associated with an increase in accommodation as Acc. And Conv. are habitually synergic in there activities so the two functions tend to vary in parallel, it is thus typically found in uncorrected hypermetropes, and less frequently in recently corrected myopes who are using accommodation for the first time. 2) A less dramatic degree may occur in the child starting near work for the first time or the young clerical or industrial worker starting a sedentary life of concentration. 3) Less commonly a primary type of convergence excess may arise in irritative conditions of the central nervous system such as meningeal irritation or increased labyrinthine pressure.

Symptoms of convergence Excess:
Mild degrees: 1-inability to read for long periods of time without the onset of discomfort, such as asthenopia, 2- frontal headaches, 3- tired eyes, 4- and short attention span while reading. These symptoms are frequently variable in their incidence, disappearing when the patient is well and reappearing when he is ill or fatigued. In advanced degrees, when convergence usually with accommodation goes into spasm, near work become impossible ad diplopia occur when reading.

Treatment of excess convergence: Elimination of the causal factor.
Refractive errors should be corrected along with any significant heterophoria. Near work should be reduced and every care taken that the book be held well away from the eyes with best conditions of illumination and posture. Orthoptic exercises may be tried but they are rarely effective, although considerable help may be gained by exercises inducing voluntary relaxation in which the patient looks at a distant object through two transparent slides and is taught to obtain physiological diplopia of marking on the transparencies, , a feat which necessitate relaxation of accommodation and convergence, this may be followed by divergence exercises with the amplyoscope (synaptophore).

Convergence Insufficiency
An insufficiency of convergence is a common condition of great clinical importance since conv. Is constantly called into play and indispensible for the maintenance of single biocular vision for all distances optically nearer than infinity. Absolute deficiency: may be said to be exist when the near point (in the absence of presbyopia) is greater than 11 cm from the intra-ocular baseline( 9.5 cm from the apex of the cornea) or when there is difficulty in attaining 30º degrees of convergence. Relative deficiency: Failure of convergence for particular working distance employed which is of more clinical importance.

Etiology: The etiology of convergence insufficiency is not clearly understood but is certainly varied. Among local causes anatomical conditions such as wide inter-pupillary distance may make convergence difficult, but the basis of the anomaly may well be the delayed development of a lately acquired function. 2)Accommodative difficulties is a common cause, if accommodation is not ordinarily employed, conv. Tends to suffer from disuse, and its insufficiency therefore typically in uncorrected myopes, and is seen in hypermetropes and presbyopes when their refractive error is corrected for the first time and in those suffering from accommodative insufficiency. 3)Those who cannot see clearly at close distances and therefore donot call upon convergence habitually such as marked hypermetropes, anisometropes or presbyopes can also have conv. Insufficiency from disuse.

4) At all ages, but particularly in the elderly, the binocular stimulus to converge will be interfered with by defective vision in one or both eyes in which is typically seen in a subject with some degree of senile cataract more marked in one eye than the other. 5) General disease or debility due to illness, toxic conditions, or metabolic or endocrine disorders may also be the cause of insufficiency while an intra-nasal disease is given a prominent etiological place by some writers. 6) Stress is undoubtedly a factor of importance in many cases. 7) Paresis or weakness of the medial rectus muscles is a rare cause occur in myasthenia gravis a typical example.

Symptoms: Symptoms are essentially those of “ eye strain” , particularly intensified in attempting close work which may be rendered impossible owing to blurring, diplopia and headache. Many patients suffer no discomfort, and a large proportion are worried only when an unusual amount of near work is attempted or when they are fatigued or unwell. Other patients complain continuously although their defect is small. Patients who have defective vision of one or both eyes as a precipitating factor may complains of closing one eye when reading, and such subjects often have a manifest divergence of the worst eye appears on close work. Diagnosis: The presence of orthophoria or slight exotropia for distance but angle of extropia for near is greater. The remoteness of the N.P of convergence beyond 9.5 cm ( usually 8 cm). Low amplitude of convergence below 15∆(usually ∆).

Treatment: 1- Duction Exercises with placing prisms: The patient is asked to look at an object and while his gaze is still fixed, prisms, base out, initially week and gradually increasing in strength are placed before the eyes at intervals of 5 seconds, the patient being encouraged to fuse the two images into one. These exercises may be continued at home in which the patient is given a 4∆ to practice for a week , and this may be augmented by 2∆ at weekly intervals. These exercises are done for distant vision , and then the object is brought nearer and exercises at the N.P and F.P are alternated. Course of orthoptic treatment including vergence exercises with the amplyoscope (synaptophore) may be used in more recalcitrant cases and are frequently rapidly effective.

These may be supplemented by simple conv
These may be supplemented by simple conv. exercises carried out at home whereby the patient attempts to approximate the N.P by fixing an object as it approaches his eyes until it appears double. In cases wherein temperament or stupidity dose not hamper co-operation. Fusion (conv.) up to 50 or 60 degrees and abolition of the symptoms are usually attained from 2 to 6 weeks. In the training of voluntary conv. The patient demonstrate to himself physiological diplopia by holding a pencil in front of his eyes he sees two pencils while fixing a distant object ,when he looking at the pencil he sees two objects and as the pencil is moved backwards or forwards the objects separate and approximate, while this is being done the pencil is removed and the patient without moving his eyes tries to retain أَبْقَىthe two objects apart as long as possible.

2- As spectacles are concerned –if they are required- hypermetropes should be given an undercorrection and myopes should be fully corrected, particularly for reading, in order to stimulate accommodation and with it convergence. When these and exercises fail that relieving prisms, base in, should be prescribed in spectacles for near work, in which case sufficient prismatic correction should be incorporated to bring the convergence just within the area of comfort (the two thirds of the total relative convergence), this is most usually needed for: Presbyopes who have insufficient converging power for near vision, and The elderly in whom the practicalities of orthoptic exercises or more extensive treatment are precluded. ممَنَوعَ

Methods of measurement AC/A ratio
Gradient Method: The patient is asked to look at a fixed distance and the lateral deviation is measured using prism alternate cover test firstly without any lens apart from the person’s own RE correcton if any. Then the deviation is measured again after the interposition of lenses (any pair of minus lenses but – 2.00 D provide a reasonable stimulus for most patients) of identical power in front of each eye. The ratio is found out from the formula: Where AC = Accommodative-Convergence in prism dioptre A = Accommodation in dioptre ∆L = Deviation in prism dioptre when lenses are put ∆O = Original deviation in prism dioptre without lenses D = Power of lens used in dioptre AC/A = ∆L - ∆O D

Where AC = Accommodative-Convergence in prism dioptre
Heterophoria Method: Heterophoria is measured at 6m “infinity” and then at 0.33 m using prism alternate cover test and the patient must wear his RE correction Where AC = Accommodative-Convergence in prism dioptre A = Accommodation in dioptre ∆N = Near deviation in prism dioptre ∆D = Distant deviation in prism dioptre D = near fixation distance in dioptre (accommodation) = 100/33 (or 1/0.33) = 3.00D AC/A = IPD + ∆N - ∆D D

Paediatric eye examination
Now, I want to take you through the different considerations and important aspects of testing young children. For any parent, a first eye examination generally arises because: - they have concerns regarding the child’s eyes or vision, - there is a family history of an eye condition, - or they have been informed that their child may have an eye problem , for example, by a health care professional

Effects of Crowding Crowding phenomenon – process where single letter acuity better than that measured by ‘crowded’ letters. Crowding more sensitive measure Amblyopia more susceptible to crowding effects

Vision To correctly interpret a child’s visual results one needs to know the normal range of vision for that age. If a difference in acuity is found between eyes, one should relate this to other findings, i.e. refractive error, binocular function or strabismus, stereopsis, ophthalmoscopy etc

Normal levels of vision
Preferential looking tests (Mayer et al 1995) 1 cpd at newborn 6-13 cpd at 1 yr Cardiff acuity test (Monocular; Adoh & Woodhouse 1994) 12-18 months to LogMAR months to LogMAR 24-30 months to LogMAR 30-36 months to LogMAR

Normal levels of vision
Kay pictures (singles) (Binocular; Deves et al 1996) 24 mths to 3 years to LogMAR letter acuity (Monocular; Sonksen et al 2007) 3yrs to LogMAR 4yrs to LogMAR 5 yrs to LogMAR 6 yrs to LogMAR 7 yrs to LogMAR

Repeatability of visual measure
What is a significant difference between eyes or between visits? It depends on how you’ve tested vision... Keeler cards 2 cards Cardiff acuity test 2 cards Kay pictures 2 lines Snellen acuity 3 lines LogMAR acuity test 4 letters (Saunders et al 2002)

Co-operation It is often useful to note the level of co-operation of the child. This helps in comparing results found in future tests. Note whether the child is tiring or not. Often you get good co-operation for one eye and then the child gets bored. You may not get everything at the one visit, so getting the child back to test the other eye is feasible.

Measurement of Refractive error
There are several ways of assessing refractive error Cycloplegic retinoscopy Mohindra retinoscopy Distance static retinoscopy

Cycloplegic refraction
Often referred to as the ‘gold standard’ method Paralyses accommodation – allows ‘full’ hypermetropia to be measured Some may argue all children should have a cycloplegic refraction. Definitely indicated where unexplained reduction in VA (in one or both eyes), strabismus or large phoria, poor stereopsis, first examination…. Workshop on cycloplegic later today

Mohindra retinoscopy Also a useful method. Utilises fact that in a totally dark room your (dim) retinoscope light is not an accommodative target. Work distance is 50cm. However, subtract -1.25DS from the result. However, children often don’t like the dark! Again, workshop on this later

Distance static retinoscopy
Useful in older children. Relies on the child’s co-operation to fixate on a distant target. Can be used in subsequent visits if child has a stable prescription.

What is a significant refractive error?
It depends on: Age Binocular status Visions Anisometropia found

Hypermetropia – prescribing guidelines
Infants are born hypermetropic. Correction in the first year could interfere with emmetropisation. Only correct refractive error in infancy if hypermetropia is high. Uncommon for hypermetropia to persist after 2 years. Amount of correction depends on other factors, i.e. presence of strabismus, amblyopia etc.

Astigmatism – prescribing guidelines
It is common to find amounts of astigmatism in infancy. This tends to resolve by the age of 1-2 years. Large amounts of astigmatism (>2.50DC) over the age of 1 year should be corrected Persistent astigmatism (> 1.50DC) at 2 years and older should be corrected.

Anisometropia – prescribing guidelines
Anisometropia is a difference in prescription between the two eyes. It is usually defined as difference of +/- 1.00D or more. Consider with other findings - If anisometropia is found in conjunction with amblyopia and/or strabismus, correction of refractive error will likely help treat this. If not prescribing full correction, one needs to keep the anisometropic difference constant

Myopia – prescribing guidelines
Myopia is uncommon in infancy. Small amounts of myopia tend to be left uncorrected initially as a child’s world is near. As a child get older, some develop myopia. A lot of research into why myopia prevalence is increasing. Ethnicity plays an important role.

Strabismus In the UK, if a strabismus is found, the community optometrist can begin the process of correcting any significant refractive error. The child is then usually referred for ophthalmological/orthoptic treatment in a hospital setting. Treatment may include correction of refractive error, patching and/or surgical correction

Dispensing Commonly spectacles are dispensed, however contact lenses may also be indicated if the level of anisometropia is high, or the refractive error is very high. Important to provide appropriate fit of spectacles – often the most troublesome part! Need to consider the thickness and weight of lenses.

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