2 Content Define visual acuity (VA) VA assessment in children VA tests Recording VA thresholdFactors influencing VA
3 Visual Acuity (VA) Definition The ability of the individual to discriminate detailAbility to resolve a pattern into spatially separated elementsDenotes the size of detail that can just be resolved by an individualVisual resolution
4 How can a 4 month baby’s visual acuity be assessed? Can hold head upSit on own
5 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?
6 Forced choice preferential looking Based oninfants prefer fixating a patterned surface over a blank surfaceKeeler or Teller acuity cards15 cards with black-&-white stripes on right or left side1 blank card4mm hole in centreKeelerTellerKeeler – circleTeller- square
7 Forced choice preferential looking Square-wave gratings of different spatial frequencySpatial Frequency = c/degThe narrower stripesHigher SFHigher VA thresholdRange c/degThe 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
8 Forced choice preferential looking MethodTesting distance 38cm‘Staircase’ procedure1 octave: difference 0.22 & 0.44 c/deg½ octave: difference 0.22 & 0.33 c/degSuitability8 weeks to 12 monthsPatients with mental & physical disabilitiesThe 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.
9 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.
10 Lea Gratings Paddles Recommended Children < 1 year Children and adults with disabilitiesAdvantageFast to performPortableBetter 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.
11 How can a 1½ year toddler’s visual acuity(VA) be assessed?
12 Cardiff Acuity Cards Design VA range Grey cards with familiar pictures Vanishing optotypesPicture beyond acuity threshold = invisiblePictures at top or bottom3 cards for each acuity levelVA range6/60-6/6 fixing at 1m6/120-6/12 fixing at ½mThe 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.
13 Cardiff Acuity Cards Method Occlude 1 eye Present cards at eye level Begin with card with widest target (lowest acuity)Observe eye movementsMasked2 out of 3 correct responsesMethodThe test must be carried out under good illuminationThe 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
15 Kay Pictures Design Series of pictures Kay Pictures Single pictures of ↓size in flip-over booksBased on same principle as Snellen Acuity TestPerformed at 6mKay Picture single logMARBased on same principle as logMAR Acuity TestPerformed at 3mKay Picture crowded logMAR4 pictures of ↓sizeLinear testBased on same principle as logMAR acuity testsThe 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.
16 Kay Pictures Method Kay Picture single logMAR Occlude 1 eyeKey card3mShow pictures of ↓sizeChoice of 3-4 pictures for each acuity levelVA range 1.00 to 0.00 logMARKay Picture crowded logMAR2+ pictures seen show smaller picturesCount number of pictures seen on smallest row of picturesVA range to logMARThe 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.
17 New Kay Picture TestChanged pictures to most easily recognised by 420 children.Comparable and similar repeatability to other visual acuity tests (O’Connor et al 2016)
18 Alternative tests for young children Lea symbolsLandolt CE chartsSingle Sheridan Gardener
19 Lea Symbols Design Based on same principle as logMAR acuity tests Linear test4 symbolsSquare, house, circle appleKey cardThe 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 +
20 Lea Symbols Method Test performed at 3m Occlude 1 eye Key card Point to symbols from top of chartCount number of symbols seen on lowest line of symbolsVA range 0.10 to 2.00 logMARCrowdedSingle
21 Landolt C/ E charts VA test targets termed optotypes Design Method Based on grid pattern5 units high & 5 units wideMethodGap of E & C in 4 waysUp, down, right or left sideIndicate direction of E or CPerformed at 6mKey cardTest 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 SnellenThe 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.
22 Single Sheridan Gardener DesignFlip-over book with single letters of ↓size7 lettersO, A, T, X, U, H, VMatching key cardPerformed at 6mPatient with poor VA ~ test can be performed at closer distancesLinear S.G. chart is also availableVA range 6/60 - 6/4The 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.
23 How can you assess a patient with very poor visual acuity? BabiesChildren/ AdultsThe 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.
24 Tests rarely used for babies or children Hundreds & ThousandsFfook’s symbolsSheridan´s rolling ballsStycar toysSjögren hand testCatford Oliver DrumHundreds 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 projectedthrough a central aperture, measuring 4x6 cm.
25 New test for infants Mirror Test Infant held 20cm from a mirror (on parent lap)Orthoptist decides if infant attends to own reflectionSlowly 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 resultTesting distanceuse 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
26 Mirror test – normative values AgeTeller acuity (FCPL)(c/deg)Snellen equivalentTesting distance x 2 (cm)95th percentile lower confidence limit (cm)1.29 days0.336/54015.5132 weeks16/18038.224.56 weeks26/9057.23711 weeks36/6072.5474.2 months46/4585.555.55.8 months56/3697.562.517 months106/1814793.58 years306/6279180.5Only data testing with both eyes openAdvantages: does not require motion or sound by examiner – minimise biasModified from Bowman et al (2010)
29 Measurement of visual acuity Visual Acuity (VA)Ability to resolve a pattern into spatially separated elementsMeasurement of VARelated to visual angle subtended at the nodal point (N) of the eyeObjects subtend different angles depending on distance from eyeRecap VA is defined as the Ability to resolve a pattern into spatially separated elementsMeasurement of visual acuity is related to the visual angle subtended at the nodal point of the eyeThe 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 ChartN
30 Limits of Visual Acuity Optical factorsDiffraction phenomenonNeural factorsAnatomical structure of retinal photoreceptorsFoveal region in retina achieve highest visual resolution (VA) due to neighbouring cones are closely togetherInteractions b/w neurons in retina & visual pathwayNThe limits of VA are imposed by optical and neural factorsOptical 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 factorsAnatomical structure of retinal photoreceptorsFoveal region in retina achieve highest visual resolution (VA) due to neighbouring cones are closely togetherInteractions b/w neurons in retina & visual pathway
31 Factors affecting your VA Size of pupilOptical aberrationsRegion of retina stimulatedLuminance of the test typeContrast b/w optotypes and backgroundLegibility of lettersFamiliaritySpacing between letters
32 Factors affecting VA Best vision at central fovea Retinal sensitivity decreases with distance away from the foveaPatients who can’t use their fovea have much poorer VA
33 Factors affecting your VA Hill of VisionFoveaFixate centrallyBlind spotVA reduces towards peripheryFixate other parts of retinaEccentric fixationThe 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 eccentricityThe peak = fovea with max sensitivityThe VF is described as an island of vision in a sea of darkness
34 Different acuity measures Minimum visibleAbility to perceive the presence of a single targetMinimum detectable (‘distinguishable’)Ability to identify features or internal arrangements in a visible targetMinimum separableAbility to detect spatial separation between adjacent lines i.e 2 lines are separated by an intervalBlack-&-white grating testsVA 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 skyHyperacuity 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
35 Different acuity measures HyperacuityAbility to perceive the alignment and orientation of linear stimuliVernier acuityMinimum recognisableAbility to determine the smallest optotypesSymbols, pictures, lettersSnellen and LogMAR chartsHyperacuity 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
36 Snellen ChartSnellen = visual angle subtended at the nodal point of the eye by altering the size of the component parts of a letterSnellen 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
37 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 eye6/6Numerator (d) = Test distanceDenominator (D) = Distance at which each component of a letter subtends 1 minute of arc at the nodal pointVA = 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
38 Snellen Letter Construction Each component of a letter subtends 1 minute of arc at the nodal point1 cone stimulated & 1 cone gap for appreciationWhole letter subtends 5 minute of arc at the nodal pointMany can actually discriminate 0.5 min of arcThe 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 6/6Testing distance 6m
39 Normal VA level - Snellen 6/6d/Dd = 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
40 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
41 What size is each component of a letter? 6/12 line6 test distance/ subtend visual angle of 1 min of arc at 12m6/24 line6/36 lineA 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 arcA 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 arcSo whole component of a 6/24 letter is 4x4 = 16 min of arc
43 Snellen Method Patient seated at 6m Wearing refractive correction Occlude 1 eyeAsk patient to read lettersLowest line is recordedTest repeated for other eyeEnd letters are easier to see than central letters for patients suffering with crowding/amblyopia
44 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?
45 Problems with Snellen Some letters easier to read / guess than others Spacing varies - no crowding of top lettersBig difference between top row and next row
46 What is logMAR?logMAR =logarithm of the Minimum Angle of ResolutionMinimum Angle of Resolution(MAR) is that subtended by each part of the letterMAR = the angular size of detail within the optotype at thresholdFor most optotypes the size of the critical detail is taken as 1/5 of the letter height
47 LogMAR Tests Introduced by Bailey and Lovie (1976) Aim Design a VA chart where the task is the same at each leveli.e size is the only variableEarly Treatment Diabetic Retinopathy Study (ETDRS) chart“gold standard” testLogMAR chartsFive letters per rowBetween letter & between row spacing proportional to letter sizeConstant ratio of size progression (0.1 logMAR steps)Approximately equal legibility of letters at each size level
48 LogMAR Charts Each letter is given a score of 0.02 logMAR One line of letters a score of 0.1 logMARScoring: letter-by-letter
49 Bailey-Lovie and ETDRS chart ‘Gold standard’ DesignBased on British standard lettersTesting distance 6mETDRSDesignSloan lettersTesting distance 4m (3m)
50 Convert logMAR to Snellen 6/6016/480.96/380.86/300.76/240.66/190.56/150.46/120.36/9.50.26/7.50.16/60.06/4.8-0.16/3.8-0.26/3-0.3
51 LogMAR Charts Method Termination rule Recording Able to read 3 on 1 line – check next lineRecordingPatient sees all 5 letters on 0.00 logMAR line viewing with right eyeVA sgls R logMARPatient sees 4 of the 5 letters on 0.00 logMAR line viewing with right eyeVA sgls R logMARThis 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
52 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 0.60But add 0.02 for each letter wrongly named.= (0.02 x 2)=0.64
53 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) = 0.16VA cgls L logMARThis 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
54 Advantages of logMAR Chart distance can be varied Bailey-Lovie chart usually tested at 6 metresETDRS logMAR chart usually tested at 4 metres2 lines difference always means the sameValues can be averaged and statistically analysedVA level can be given by the number of letters recognised on a particular lineLetter-by-letter scoreAs each letter is given a score of 0.02 LogMAR (or LogMAR if 4 letters e.g. LogMAR crowded test)
56 Crowded logMAR acuity test Glasgow acuity testDesign on principle of Bailey LovieCrowded book4 letters inside a crowding barUncrowded book2 letters at each acuity levelEach letter has a score of logMAROne 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.
57 Crowded logMAR acuity test Who is it suitable for?Preschool children3-5 years oldMethodTested at 3mPractise for near with key cardSmallest row of letters/ number of letters seen recorded
58 Sonksen logMAR Test Designed by University College of London Based on principle of ETDRS chartSimilar to crowded logMAR test2 Flip-over booklets4 letters surrounded by a crowding barO, X, H, T, U, VTraining bookletKey cardTesting distance 3mNear test chartBased on principle of EDTRS chart (Based on principle of EDTRS chart and thus accord with adult standards)Constant contour interaction4 letters surrounded by a crowding barO, X, H, T, U, VTHESE LETTERS ARE CONSIDERED THE EASIEST FOR YOUNG CHILDREN TO MATCH
59 Near VA tests Near VA tested at 33cm or 40cm If distance chart design & luminance levels are comparable to near test designnear VA score = distance VA scoreprovided eye accommodated and refractive correction wornto allow good focus for a retinal imageTwo different types of near VA testsNear 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.
60 Near VA Tests Typeset material Common tests Similar to print in newspapers or booksarranged in sentences, paragraphs or wordsNot comparable to distance VA testsCommon tests“N” Test Types (Times Roman Print)Moorfields bookMaclure bookBased on principle of being equivalent to distance chartReduced SnellenLogMAR chartNear single Kay picture and crowded Kay picture logMAR cardsLea symbolsSingle S.G.Landolt C & E chartsThe 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 bookMaclure bookThe 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
61 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?TestingKeep the correct testing distanceDo not allow peepingOccluding patch on face not glassesOcclusive sunglassesTest with refractive correction if wornEncourage patient if limited co-operationRecord test used, cgls or sgls