2. Refraction1-lab

3. The routine of testing visual acuity (VA)
The test type should be clearly printed.
The test type should be legible.
The test type should be uniformly illuminated.
The distance between the patient and the chart is 6 meters or 20 feet.
If this distance is unavailable the patient site 3 meters 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 right eye (R.E.) should always be tested firstly except if the left eye (L.E.) has a complaint of defective vision (D.V.)

4. 8. The patient reads down the chart using his right eye (OD), his left eye (OS) as far as he can, then he repeats the test with both eyes (B.E.) 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 Rt (O.D=Oculus Dexter) 6/9 Lt (OS=Oculus Senester) 6/9 BE (OU= Oculus Utrique) 6/6 9. 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 6/60 the case called legal blindness.

5. 10. If he could not see the letter 60 from a distance one meter the chart becomes useless. In a good illuminated room we ask him to count the examiner's hand fingers at 1 m or less if he can, his V.A. is counting fingers (C.F.), each eye V.A is assessed separately. 11. If he could not count fingers in front his eye, the examiner moves his fingers against a dark background such as his coat and ask him what can you see, if he can see the moving fingers, his V.A. is hand movement (H.M.). 12. 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 perception of light (P.L).

6. 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
13. If he could not see the light his V.A. is complete blindness and the eye is a hopeless eye (NO PL)
14. The ordinary V.A. test depends upon the cooperation of the patient, thus it fails in:
Malingerers:
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.

7. B. In illiterates: 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). C. Young children For those we use the familiar figures of varying sizes as ship, car, bird, cow, the child has a card containing the same figures in the chart and he is asked just to mention the figure which is similar.

8. Objective methods of refraction (Retinoscopy)
Trial Frame (T.F.) is used to carry the trial lenses during objective and subjective refraction.
T.F. should be clean, light and easily adaptable allowing the adjustment for each eye separately.
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 centred.

9. Anteroposterior adjustment is possible as well as vertical , and horizontal adjustments.
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.
Simplicity to ensure (make certain), lightness and comfort fitting and 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.
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.

10. These cells should be close together as possible as a considerable space between the lenses may result in some errors in results.
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 of the visual line.

11. Trial Lenses
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).
Then plus and minus spheres every 1/2 to 6Ds (4.50, 5.00, 5.50, 6.00 Ds).
There after plus and minus spheres every 1 to 14 Ds : (7.0, 8.0, 9.0, 10.0, 11.00, 12.0, 13.0, 14.0Ds).
Then plus and minus spheres every 2 diopters to 20 Ds (16.0, 18.0, 20.0) Ds.

12. Trial Lenses
Plus cylinder
Minus cylinder
Plus
sphere
Minus
sphere

13. It also contains plus and minus cylinder every 1/4 to 2Dc (0. 25, 0
It also contains plus and minus cylinder every 1/4 to 2Dc (0.25, 0.50, 0.75, 1.0, 1.25, 1.50, 1.75, 2.0Dc) Then every 1/2 to 6 Dc. (2.50, 3.0, 3.50, 4.0, 4.50, 5.0, 5.50, 6.0)Dc.
By a combination of sphere and cylinder an excellent range of optical effect is obtained.
The trial set contains also prisms up to 10 DP then 15 and 20 DP. (1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0, 15.0, 20.0) PD.
It also contains accessories as plano lenses ,opaque (occluders), pin hole, staenopic slit discs , Maddox rod , red and green filters, centering devices and others.

14. The practise of retinoscopy
The room should be long and darken to relax the accommodation of the patient’s eye.
The patient is instructed to look past the head of the examiner in a direction opposite to that of the examined eye.
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.

16. In either event , in cases of squint one or either eye should be occluded to avoid the deviation of the examined eye.
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.
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.
The examiner directs the light of the retinoscopy into the pupil of the patient.
Slow tilting of the retinoscope is started , noting the red reflex regarding:-

17. 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
The brilliance, speed of movement and size of the reflex differ according to the (RE) of the patient’s eye.
The reflex is brightest near neutrality and in small RE, but dull in high errors.
The reflex is more rapid when the R.E is small and slower when the error is great.
The reflex is wide in small errors and thinner in great errors.