Visual Acuity Anne Bjerre October 2016.

Visual Acuity Anne Bjerre October 2016

Content Define visual acuity (VA) VA assessment in children VA tests
Recording VA threshold Factors influencing VA

Visual Acuity (VA) Definition
The ability of the individual to discriminate detail Ability to resolve a pattern into spatially separated elements Denotes the size of detail that can just be resolved by an individual Visual resolution

How can a 4 month baby’s visual acuity be assessed?
Can hold head up Sit on own

If you suspect vision might be very poor…..
How do parents think the baby sees? Does the baby make eye contact? Does the baby respond to or copy facial expressions? Does the baby notice if you switch the room lights on/off? Do the baby’s pupils react to light?

Forced choice preferential looking
Based on infants prefer fixating a patterned surface over a blank surface Keeler or Teller acuity cards 15 cards with black-&-white stripes on right or left side 1 blank card 4mm hole in centre Keeler Teller Keeler – circle Teller- square

Square-wave gratings of different spatial frequency Spatial Frequency = c/deg The narrower stripes Higher SF Higher VA threshold Range c/deg The grating you see on the cards are sine-wave gratings of different spatial frequencies (black-and-white stripes of different widths) on the left or right side. Spatial frequency is measured in cycles per degree. One spatial cycle is a black and white grating (stripe) together, per degree is the number of cycles per degree at the nodal point of the eye. The narrower the stripes the higher spatial frequency and the highest spatial frequency seen is a measure of the visual acuity threshold. The gratings on each acuity card ranges from 0.32 to 38 cycles per degree (c/deg). 1 spatial cycle = 1 black + 1 white stripe

Method Testing distance 38cm ‘Staircase’ procedure 1 octave: difference 0.22 & 0.44 c/deg ½ octave: difference 0.22 & 0.33 c/deg Suitability 8 weeks to 12 months Patients with mental & physical disabilities The child is seated on parent’s knee at a testing distance of 38cm. The examiner is seated behind the screen, presents the acuity cards and views the infant’s face through the 4mm peephole in each card in order to establish if the infant fixates the gratings to the right or left. The cards are presented masked to the examiner in order to eliminate bias to which side the infant is fixing. It is recommended to present the cards in a staircase ‘up-and-down’ fashion. The grating card with lowest spatial frequency (thickest stripes) is presented first, moving up in 1-2 octave or half octave steps depending on the infant’s response. One octave is equivalent to the difference between the 0.22 and 0.44c/deg card, half an octave is the difference between the 0.22 and 0.33c/deg cards. If an incorrect response is noted a lower spatial frequency card is shown. Two incorrect responses with a card suggests the grating is probably not seen. If the infant loses concentration or the examiner is unsure of the response the grating cards can be shown vertically. This test is suitable for infants from 8 weeks (but possible earlier) up to approximately 12 months. It can also be useful in children with mental disabilities.

Lea Gratings Paddles Design FCPL tested at 57cm
Frequency of black stripes given in cycles per centimetre = cycles per centimeter (cpcm) LEA GRATINGS are for preferential looking test situations with infants or children and adults with disabilities to determine detection acuity. Grating levels printed on each handle are: 0.25, 0.5, 1.0, 2.0, 4.0 and 8.0 cpcm (cycles per centimeter of surface). Includes instructions and storage case. 4 paddles 8" (20 cm) in diameter. The score at 29cm and 86 cm is also given on the paddle.

Lea Gratings Paddles Recommended Children < 1 year
Children and adults with disabilities Advantage Fast to perform Portable Better fixation in < 1 year old compared to using Cardiff Cards (Mody et al 2012) LEA GRATINGS are for preferential looking test situations with infants or children and adults with disabilities to determine detection acuity. Grating levels printed on each handle are: 0.25, 0.5, 1.0, 2.0, 4.0 and 8.0 cpcm (cycles per centimeter of surface). Includes instructions and storage case. 4 paddles 8" (20 cm) in diameter. The score at 29cm and 86 cm is also given on the paddle.

How can a 1½ year toddler’s visual acuity(VA) be assessed?

Cardiff Acuity Cards Design VA range Grey cards with familiar pictures
Vanishing optotypes Picture beyond acuity threshold = invisible Pictures at top or bottom 3 cards for each acuity level VA range 6/60-6/6 fixing at 1m 6/120-6/12 fixing at ½m The test employs the principle of vanishing optotype: the targets are pictures (duck, house, fish, car, train, boat dog) drawn with a white band bordered by two black bands, of half the width, on a neutral grey background. The average brightness (luminance) of the picture is equal to that of the grey background. If the picture lies beyond the acuity limit, the picture blends with the grey background and becomes invisible. The visual acuity is given by the narrowest white band for which the target is visible to the child. The Cardiff acuity test consists of grey cards with a simple picture located at the top or the bottom of the card. There are 3 cards for each of the 11 acuity levels.

Cardiff Acuity Cards Method Occlude 1 eye Present cards at eye level
Begin with card with widest target (lowest acuity) Observe eye movements Masked 2 out of 3 correct responses Method The test must be carried out under good illumination The child is seated on a chair or on a parent’s lap, wearing their refractive correction. One eye is occluded with a patch, ensuring that the patient is unable to peep around the patch. The examiner presents the cards at eye level at a distance of 1 metre. A testing distance of ½ metre may be used to allow better co-operation or obtain lower acuity. The examiner begins presenting the card with the widest target (lowest acuity), and from the child’s eye movements, the examiner estimates the position (top or bottom) of the picture. There are 3 cards for each acuity level and two correct responses are required to proceed to the next acuity level. If an incorrect response is found the test is repeated with a larger target. The end-point should be taken as the highest acuity level at which at least two out of three card from same acuity level are scored correctly. It is important the examiner is masked to the position of the pictures. In order to keep the child’s attention, the examiner can talk about the pictures, encourage to point and name the pictures. The test is repeated occluding the other eye

How do you assess VA in a 2½ old child?

Kay Pictures Design Series of pictures Kay Pictures
Single pictures of ↓size in flip-over books Based on same principle as Snellen Acuity Test Performed at 6m Kay Picture single logMAR Based on same principle as logMAR Acuity Test Performed at 3m Kay Picture crowded logMAR 4 pictures of ↓size Linear test Based on same principle as logMAR acuity tests The Kay picture test comprises of a series of pictures based on the same principle as Snellen’s test; the width of the lines making up the pictures is equivalent to the letters on the Snellen chart. Single pictures of decreasing size in flip-over books are available for use at 3 and 6 metres. This test is usually performed at 6 metres. The visual acuity ranges from 6/60 to 6/6. Pictures which have proven to be easily recognisable by young children are presented, including duck, house, apple, fish, van, clock, cup and boot. A matching key card with the pictures is provided. The Kay picture crowded LogMAR book is designed on the same basis as LogMAR tests and aims to enable linear acuity measurement before letter tests are possible. Eight pictures of decreasing size are presented in groups of four (except sizes 1.0 and 0.9 where there are two per line) in a flip-over book. Visual acuity is measured in twelve equal steps 1.0 to -0.1 LogMAR. The test is performed at 3 metres. A matching key card with the 8 pictures (duck, house, apple, fish, van, clock, cup and boot) is provided.

Kay Pictures Method Kay Picture single logMAR
Occlude 1 eye Key card 3m Show pictures of ↓size Choice of 3-4 pictures for each acuity level VA range 1.00 to 0.00 logMAR Kay Picture crowded logMAR 2+ pictures seen show smaller pictures Count number of pictures seen on smallest row of pictures VA range to logMAR The examiner shows the page with the largest pictures in the book, points to the first picture in the row and asks the patient to name or match the picture. This is repeated pointing to another picture in the row. If two or more pictures can be seen, pictures of decreasing size are presented and the test repeated. If none or only one picture can be seen, the examiner shows the next size larger pictures and repeats and checks all four pictures. The row of smallest picture or the number of pictures in the row of smallest picture that can be correctly named is recorded.

New Kay Picture Test Changed pictures to most easily recognised by 420 children. Comparable and similar repeatability to other visual acuity tests (O’Connor et al 2016)

Alternative tests for young children
Lea symbols Landolt C E charts Single Sheridan Gardener

Lea Symbols Design Based on same principle as logMAR acuity tests
Linear test 4 symbols Square, house, circle apple Key card The Lea symbols acuity test is designed on the same basis as the LogMAR charts and aims to enable linear acuity measurement before letter tests are possible. Four different symbols, square, house, circle and apple, are presented on the chart. The distance between the symbols, the optotypes, is equal to the width of the symbols. From line to line the symbols decrease in size in 0.1 LogMAR steps. Visual acuity ranges between 0.1 and 2.0 LogMAR. The test is performed at 3 metres. A matching key card with the four symbols is provided. Lea symbols are also available as single symbols and crowded symbols books. A. Distance VA test for testing 2-4 year olds B. Distance VA test for testing children 4 years +

Lea Symbols Method Test performed at 3m Occlude 1 eye Key card
Point to symbols from top of chart Count number of symbols seen on lowest line of symbols VA range 0.10 to 2.00 logMAR Crowded Single

Landolt C/ E charts VA test targets termed optotypes Design Method
Based on grid pattern 5 units high & 5 units wide Method Gap of E & C in 4 ways Up, down, right or left side Indicate direction of E or C Performed at 6m Key card Test targets (e.g. letters such as E and C) used for visual acuity tests are often termed optotypes. Most letters used for visual acuity testing are designed based on a grid pattern that is 5 units high and 5 units wide. The principle of these tests is the same as Snellen The gap of the E or C is presented in 4 ways; up, down, to the right or to the left and the patient is requested to indicate the direction of the E or C. The test is performed at 6 metres.

Single Sheridan Gardener
Design Flip-over book with single letters of ↓size 7 letters O, A, T, X, U, H, V Matching key card Performed at 6m Patient with poor VA ~ test can be performed at closer distances Linear S.G. chart is also available VA range 6/60 - 6/4 The single Sheridan Gardiner (S.G.) test consists of a flip-over book with single letters of decreasing size. A matching key card with 7 letters is provided. The 7 letters on the card are O, A, T, X, U, H, V. The test is used at 6 metres but can also be performed at closer distances if the patient has poor visual acuity. A linear Sheridan Gardiner chart is available for use at 6 metres, comprising of 3 letters per line and the same 7 letters as single S.G. If a child can co-operate well enough using the linear S.G. chart a LogMAR test or Snellen chart should be tried.

How can you assess a patient with very poor visual acuity?
Babies Children/ Adults The optokinetic drum can be used in inattentive babies, the stripes are held vertically and the drum is rotated slowly in front of the patient. The patient will demonstrate eye movements consisting of a following movement as the patient fixates on 1 stripe followed by a a rapid re-fixation movement to the next stripe.

Tests rarely used for babies or children
Hundreds & Thousands Ffook’s symbols Sheridan´s rolling balls Stycar toys Sjögren hand test Catford Oliver Drum Hundreds and Thousands. Cake decorations may be used to compare the visual acuity between eyes, and as a rough estimate. The child's pincer grip must have developed for them to perform this test. The hundreds and thousands are presented to the child on the hand of the examiner and their ability to pick these up observed. One piece only can be placed in one hand and none in the other hand to judge whether or not the child can see the 'sweet'. Beale Collin's Pictures: is a picture test for use at 6m. Ffook's Symbols: comprise of single shapes of varying size (triangle, circle or square). The shapes are presented on a cube or as a chart, and the child is requested to match them Visual acuity ranges from 6/60 to 6/6 and is suitable for measuring visual acuity in children of about 2½ years of age. Sheridan’s Rolling Balls: Graded sized balls for use at 3 metres. May be spun or rolled or mounted on sticks for presentation from behind a screen. Stycar Toys: Toys of graded sizes presented at 3 metres for the child to match. The Catford drum consists of a motor driven drum with separated black dots of various sizes on a white background projected through a central aperture, measuring 4x6 cm.

New test for infants Mirror Test
Infant held 20cm from a mirror (on parent lap) Orthoptist decides if infant attends to own reflection Slowly moved further away until fixation lost (i.e. head or eyes turning away) Tested 5 times, low and high value discarded and mean of remaining 3 recorded as result Testing distance use measuring tape (2x actual distance) Better attention with wall-mounted (92%) versus hand-held mirror (62%) Because of reflection the testing distance is twice the distance from child from child to mirror

Mirror test – normative values
Age Teller acuity (FCPL) (c/deg) Snellen equivalent Testing distance x 2 (cm) 95th percentile lower confidence limit (cm) 1.29 days 0.33 6/540 15.5 13 2 weeks 1 6/180 38.2 24.5 6 weeks 2 6/90 57.2 37 11 weeks 3 6/60 72.5 47 4.2 months 4 6/45 85.5 55.5 5.8 months 5 6/36 97.5 62.5 17 months 10 6/18 147 93.5 8 years 30 6/6 279 180.5 Only data testing with both eyes open Advantages: does not require motion or sound by examiner – minimise bias Modified from Bowman et al (2010)

Any questions?

Visual Acuity II Anne Bjerre October 2016

Measurement of visual acuity
Visual Acuity (VA) Ability to resolve a pattern into spatially separated elements Measurement of VA Related to visual angle subtended at the nodal point (N) of the eye Objects subtend different angles depending on distance from eye Recap VA is defined as the Ability to resolve a pattern into spatially separated elements Measurement of visual acuity is related to the visual angle subtended at the nodal point of the eye The visual angle is created by rays of light crossing at the nodal point of the eye. An object subtends different angles depending on the distance it is from the eye, the visual angle is also changed by changing the size of the object or the size of the component parts which is utilised using the Snellen Chart N

Limits of Visual Acuity
Optical factors Diffraction phenomenon Neural factors Anatomical structure of retinal photoreceptors Foveal region in retina achieve highest visual resolution (VA) due to neighbouring cones are closely together Interactions b/w neurons in retina & visual pathway N The limits of VA are imposed by optical and neural factors Optical limitation: when an emmetropic (normal) eye is in optimal focus, the image of a point object formed on retina is not a perfect point, but a blurred circular patch surrounded by a series of faint rings. This is know as the diffraction phenomenon. The light spread on the retinal image is dependent upon the pupil size. Ideally all rays converge to form a single point image on retina. Rays from different parts of the pupil diviate so the image is a patch rather than a point. Rays from the more peripheral parts of the pupil is more abberrated (blurred). Neural factors Anatomical structure of retinal photoreceptors Foveal region in retina achieve highest visual resolution (VA) due to neighbouring cones are closely together Interactions b/w neurons in retina & visual pathway

Factors affecting your VA
Size of pupil Optical aberrations Region of retina stimulated Luminance of the test type Contrast b/w optotypes and background Legibility of letters Familiarity Spacing between letters

Factors affecting VA Best vision at central fovea
Retinal sensitivity decreases with distance away from the fovea Patients who can’t use their fovea have much poorer VA

Factors affecting your VA
Hill of Vision Fovea Fixate centrally Blind spot VA reduces towards periphery Fixate other parts of retina Eccentric fixation The sensitivity of the eye is not the same across the whole visual field. The height of the island represent the sensitivity of the eye and we can see the sensitivity decrease with eccentricity The peak = fovea with max sensitivity The VF is described as an island of vision in a sea of darkness

Different acuity measures
Minimum visible Ability to perceive the presence of a single target Minimum detectable (‘distinguishable’) Ability to identify features or internal arrangements in a visible target Minimum separable Ability to detect spatial separation between adjacent lines i.e 2 lines are separated by an interval Black-&-white grating tests VA can be classified according to the criteria set for the observers response. Minimum visible: The ability to perceive the presence of a single target e.g thin wire in the sky Hyperacuity used when assessing vernier acuity, the task is to judge if 2 line segments are in line, and stereoacuity, the task is to judge if one line segment is closer or further away than the other

Different acuity measures
Hyperacuity Ability to perceive the alignment and orientation of linear stimuli Vernier acuity Minimum recognisable Ability to determine the smallest optotypes Symbols, pictures, letters Snellen and LogMAR charts Hyperacuity used when assessing vernier acuity, the task is to judge if 2 line segments are in line, and stereoacuity, the task is to judge if one line segment is closer or further away than the other

Snellen Chart Snellen = visual angle subtended at the nodal point of the eye by altering the size of the component parts of a letter Snellen expresses the visual angle subtended by altering the size of the component parts of a letter. Normal visual acuity is defined as the ability to discriminate a pattern whose detail subtends a visual angle of 1 minute of arc. The test distance is specified as the numerator (d) and the distance at which a just resolvable letter must be located to subtend 1 minute of arc as the denominator (D) thus visual acuity is defined as d/D. The letters on the Snellen chart are constructed so that each component of a letter subtend 1 minute of arc at a testing distance of 6 metres. However the whole letter will subtend 5 minutes of arc. Normal visual acuity according to Snellen is given as 6/6

Snellen Chart Normal VA Numerator (d) = Test distance
ability to discriminate a pattern whose detail subtends a visual angle of 1 minute of arc at the nodal point of the eye 6/6 Numerator (d) = Test distance Denominator (D) = Distance at which each component of a letter subtends 1 minute of arc at the nodal point VA = d/D. Snellen expresses the visual angle subtended by altering the size of the component parts of a letter. Normal visual acuity is defined as the ability to discriminate a pattern whose detail subtends a visual angle of 1 minute of arc. The test distance is specified as the numerator (d) and the distance at which a just resolvable letter must be located to subtend 1 minute of arc as the denominator (D) thus visual acuity is defined as d/D. The letters on the Snellen chart are constructed so that each component of a letter subtend 1 minute of arc at a testing distance of 6 metres. However the whole letter will subtend 5 minutes of arc. Normal visual acuity according to Snellen is given as 6/6

Snellen Letter Construction
Each component of a letter subtends 1 minute of arc at the nodal point 1 cone stimulated & 1 cone gap for appreciation Whole letter subtends 5 minute of arc at the nodal point Many can actually discriminate 0.5 min of arc The letters on the Snellen chart are constructed so that each component of a letter subtend 1 minute of arc at a testing distance of 6 metres. However the whole letter will subtend 5 minutes of arc. Normal visual acuity according to Snellen is given as 6/6 Testing distance 6m

Normal VA level - Snellen
6/6 d/D d = testing distance (6m) D = distance (6m) at which each component of a just resolvable letter is located to subtend 1 minute of arc at the nodal point

How large does the letter need to be at 12m to achieve 6/6 and for each component of the letter to subtend 1 minute of arc at the nodal point? It needs to be double the size of the letter presented at 6 metres to subtend 1 minute of arc at the nodal point of the eye

What size is each component of a letter?
6/12 line 6 test distance/ subtend visual angle of 1 min of arc at 12m 6/24 line 6/36 line A 6/12 letter is double the size of a 6/6 letter and therefore you need to multiply 1 min of arc by 2 (1x2) = 2 minutes of arc A 6/24 letter is 4x the size of a 6/6/ letter and therefore you need to multiply 1 min of arc by 4= 4 min of arc So whole component of a 6/24 letter is 4x4 = 16 min of arc

Snellen Chart Snellen notation 6/60 6/36 6/24 6/18 6/12 6/9 6/6 6/5

Snellen Method Patient seated at 6m Wearing refractive correction
Occlude 1 eye Ask patient to read letters Lowest line is recorded Test repeated for other eye End letters are easier to see than central letters for patients suffering with crowding/amblyopia

Recording VA cgls R: 6/5 - 2 L: 6/12 Sn sgls R: 6/9 + 1 L: 6/18pt Sn
In which situation is visual acuity a) best? b) worst?

Problems with Snellen Some letters easier to read / guess than others
Spacing varies - no crowding of top letters Big difference between top row and next row

What is logMAR? logMAR = logarithm of the Minimum Angle of Resolution Minimum Angle of Resolution(MAR) is that subtended by each part of the letter MAR = the angular size of detail within the optotype at threshold For most optotypes the size of the critical detail is taken as 1/5 of the letter height

LogMAR Tests Introduced by Bailey and Lovie (1976) Aim
Design a VA chart where the task is the same at each level i.e size is the only variable Early Treatment Diabetic Retinopathy Study (ETDRS) chart “gold standard” test LogMAR charts Five letters per row Between letter & between row spacing proportional to letter size Constant ratio of size progression (0.1 logMAR steps) Approximately equal legibility of letters at each size level

LogMAR Charts Each letter is given a score of 0.02 logMAR
One line of letters a score of 0.1 logMAR Scoring: letter-by-letter

Bailey-Lovie and ETDRS chart ‘Gold standard’
Design Based on British standard letters Testing distance 6m ETDRS Design Sloan letters Testing distance 4m (3m)

Convert logMAR to Snellen
6/60 1 6/48 0.9 6/38 0.8 6/30 0.7 6/24 0.6 6/19 0.5 6/15 0.4 6/12 0.3 6/9.5 0.2 6/7.5 0.1 6/6 0.0 6/4.8 -0.1 6/3.8 -0.2 6/3 -0.3

LogMAR Charts Method Termination rule Recording
Able to read 3 on 1 line – check next line Recording Patient sees all 5 letters on 0.00 logMAR line viewing with right eye VA sgls R logMAR Patient sees 4 of the 5 letters on 0.00 logMAR line viewing with right eye VA sgls R logMAR This is calculated by 1 letter was not seen on the 0.0 LogMAR line. The letter is given a score of 0.02 LogMAR. This is added to the 0.0 LogMAR line: = 0.02 LogMAR

Example A patient reads: H, V, Z, D, S, N, C, V, K, D, C, Z, S, H, N,
O, N, V, S, R, K, D, N, P, C, 2 letters incorrect on this line. Whole line worth 0.60 But add 0.02 for each letter wrongly named. = (0.02 x 2) =0.64

LogMAR Charts Recording
Patient wears refractive correction and incorrectly name 3 of the 5 letters on 0.10 logMAR line viewing with left eye (0.02 x 3) = 0.16 VA cgls L logMAR This is calculated by 3 letter were not seen on the 0.1 LogMAR line. Each letter is given a score of 0.02 LogMAR. This is added to the 0.1 LogMAR line: = 0.14 LogMAR

Advantages of logMAR Chart distance can be varied
Bailey-Lovie chart usually tested at 6 metres ETDRS logMAR chart usually tested at 4 metres 2 lines difference always means the same Values can be averaged and statistically analysed VA level can be given by the number of letters recognised on a particular line Letter-by-letter score As each letter is given a score of 0.02 LogMAR (or LogMAR if 4 letters e.g. LogMAR crowded test)

Computerised charts

Crowded logMAR acuity test
Glasgow acuity test Design on principle of Bailey Lovie Crowded book 4 letters inside a crowding bar Uncrowded book 2 letters at each acuity level Each letter has a score of logMAR One line of letters is a score of logMAR. Formerly know as the Glasgow Acuity Test. uncrowded book presents two letters, one to the right and one to the left side, at each acuity level. The crowded books comprise of rows of 4 equal sized letters surrounded by a box (‘crowding bar’). The letters on each card decreases in size by 1 log unit.

Crowded logMAR acuity test
Who is it suitable for? Preschool children 3-5 years old Method Tested at 3m Practise for near with key card Smallest row of letters/ number of letters seen recorded

Sonksen logMAR Test Designed by University College of London
Based on principle of ETDRS chart Similar to crowded logMAR test 2 Flip-over booklets 4 letters surrounded by a crowding bar O, X, H, T, U, V Training booklet Key card Testing distance 3m Near test chart Based on principle of EDTRS chart (Based on principle of EDTRS chart and thus accord with adult standards) Constant contour interaction 4 letters surrounded by a crowding bar O, X, H, T, U, V THESE LETTERS ARE CONSIDERED THE EASIEST FOR YOUNG CHILDREN TO MATCH

Near VA tests Near VA tested at 33cm or 40cm
If distance chart design & luminance levels are comparable to near test design near VA score = distance VA score provided eye accommodated and refractive correction worn to allow good focus for a retinal image Two different types of near VA tests Near visual acuity is tested at 1/3 metre. If the distance chart design and luminance levels are comparable to the near test design, the near visual acuity score is equal to the distance visual acuity score provided the eye is accommodated and refractive correction worn to allow good focus for a retinal image. There are two different types of near visual acuity tests.

Near VA Tests Typeset material Common tests
Similar to print in newspapers or books arranged in sentences, paragraphs or words Not comparable to distance VA tests Common tests “N” Test Types (Times Roman Print) Moorfields book Maclure book Based on principle of being equivalent to distance chart Reduced Snellen LogMAR chart Near single Kay picture and crowded Kay picture logMAR cards Lea symbols Single S.G. Landolt C & E charts The first uses typeset material which is similar to print seen in newspapers or books, and may be arranged in sentences, paragraphs or in a series of unrelated words. These tests are not comparable to any distance charts. Common tests include: “N” Test Types (Times Roman Print) Moorfields book Maclure book The second type of near visual acuity tests are based on the principle of the equivalent distance chart. Following distance visual acuity tests also provide a near test. Near Kay picture and Kay picture crowded LogMAR cards

Summary Decide upon suitable test Testing
Which test is suitable for the child’s age & level of concentration? Which tests are suitable for patients with very poor vision? Testing Keep the correct testing distance Do not allow peeping Occluding patch on face not glasses Occlusive sunglasses Test with refractive correction if worn Encourage patient if limited co-operation Record test used, cgls or sgls

Visual Acuity Anne Bjerre October 2016.

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