Visual acuity in children

VISUAL ACUITY IN CHILDREN
Dr Saurabh Kushwaha
Resident Ophthalmology

SCOPE
 Visual acuity
 Components of visual acuity
 Milestones of visual development
 Normal visual development
 Guidelines for visual assesment
 Vision tests for various age groups

VISUAL ACUITY (VA)
 It is the measure of the spatial resolution of
visual processing
 Also known as resolving power of eye
 Ability to differentiate two separate object as
separate and appreciate the details of visible
object

COMPONENTS OF VA
 Minimum visibility : a judgement of whether
a target is present or absent (detection acuity)
 Resolution : evidence that the spatial detail
Contained within a target has been fully
resolved (resolution acuity)
 Recognition : the identification of a target

MILESTONES OF VISUAL
DEVELOPMENT
 After birth: Can fix and follow a light source, face or large,
colorful toy
 1month : Fixation is central, steady and maintained, can
follow as low target and converge
 3 months : binocular vision and coordinated eye movements
 6 months : Reaches out accurately for toys
 9 months : Visually directed reaching Ex. look for hidden toys
 2 years : Picture matching
 3 years : Letter matching of single letters
 5 years : Snellen’s chart by matching or naming

NORMAL VISUAL DEVELOPMENT
Age VA
At birth 6/120
4 months 6/60
6 months 6/36
1 year 6/18
2 years 6/6

EXPECTED VA LEVELS
Age
(months)
OKN FPL VEP
1 20/300 20/400 20/300
6 20/60 20/150 20/20
12 20/40 20/100 20/20
36 20/20 20/20 20/20

WHY TO RECORD VA IN
CHILDREN?
 Most eye problems can be treated if
detected early
 To know if visual development is normal
 Helps decide eligibility for low vision and
rehabilitation services

GUIDELINES FOR THE
ASSESSMENT OF VA
 Cooperation and understanding the test
 Children perform best if the examination takes place
when they are alert Ex. early in the morning or after an
infant's nap
 Because infants tend to be more cooperative and
alert when feeding, it is suggested to bring a bottle for
feeding the child
 Distance vision: 3 m ; Near vision: 33 cms
 Easy symbols
 Linear visual acuity should be tested as soon as
possible (more accurate)

BLINK REFLEX TEST
 The blink to a bright light is a behavior learned
by 30 weeks of gestational age and is
occasionally present in decorticate infants.
 The blink to a threatening gesture is another
learned reflex, usually present by 5 months
 When testing, care must be taken not to brush
air against the child’s corneas and elicit a blink
by that mechanism.

PUPILLARY LIGHT REFLEX TEST
 The pupillary light response is not equivalent to
visual ability, but its presence indicates intact afferent
visual neurologic pathways to the level of the brachium
of the superior colliculus and efferent pathways to the
iris sphincter
 Visualization in very young children sometimes
requires a magnifying glass, as their pupils are smaller
than those of older children (because of decreased
sympathetic tone) and the light responses are of small
amplitude
 This reflex is present in premature babies over 29 -
31 weeks of gestational age

EYE POPPING TEST
 Sometimes very young infants don't show any
distinguishable visual behavior at all. In this case, the
eye popping reflex indicates at least the infant’s ability
to detect changes in room illumination
 When the room lights are suddenly dimmed, the
baby's upper eye lids should pop open wide for a
moment. The baby will often close its eyes when the
lights are brought back up, but will again pop its eyes
open when the lights are dimmed. This behavior is
documented as "positive eye popping".

OPTOKINETIC NYSTAGMUS
 Commonly used test in Neonates
 Test object moves in one direction
 Based on observation of Pendular eye
movements
 Slow following phase & rapid recovery phase
 Good correlation with subjective acuity
 Overestimates the visual acuity as the target is
moving

VISUAL EVOKED POTENTIAL
 VEP is the measure of change of electrical activity of
the visual cortex in response to patterned stimulus
 Checkered board or square wave grating
 VEP is useful in the determination of problems such
as amblyopia, cortical blindness and visual impairment
• Flash VEPs
• Pattern reversal VEPs
• Sweep VEPs

FIXATION BEHAVIOR TEST
 The test is performed by seating the child comfortably
in the caretaker's lap. The object of visual interest,
usually a bright colored toy, is slowly moved to the right
and to the left. The examiner observes whether the
infant's eyes turn toward the object and follow its
movements (fix and follow behavior) . The examiner can
use a thumb to occlude one of the infant's eyes in order
to test each eye separately
 If the child has a fix and follow behavior then it is
assumed that the patient could see a small target or toy
in a normally illuminated room

BINOCULAR FIXATION PREFERENCE
 Behavioral evidence of decreased vision in right eye (A) A
small toy is used to get the child’s attention, and the examiner
covers the right eye to monitor fixation of the left eye. The child
fixates on the toy without objecting (B) When the left eye is
covered, the child objects and tries to move the examiner’s
hand (C) When the right eye is covered, the child does not
object and tracks the object.

CSM
 CSM : Central; Steady; Maintenance
 ‘C’ refers to the central corneal light reflex as the
patient fixates eye on the examiner’s light and if fixation
target is viewed eccentrically then it is termed as
uncentral
 ‘S’ refers to the steadiness as the examiner’s light is
motionless and then it is slowly moved out
 ‘M’ refers to the ability of patient to maintain
alignment, first with one eye then with another
 Test is done with target at 40 cm distance
 CSM : 66 - 69
 CSNM : 636 - 660
 Unsteady central fixation : <660

PREFERENTIAL LOOKING TEST
 Most commonly used test
 Based upon turning of the head or eyes towards
the pattern rather than a uniform (homogenous) field
 Alternating black and white stripes with
progressively narrowing strips are shown randomly,
next to plain test object
 Children with better vision are able to see finer
grating and turn towards it
 Test near vision & NOT distance vision

TELLER ACUITY CARDS
 Modified form of Preferential Looking Test
 Simpler & rapid testing
 contains 17 cards
 12.5 x 12.5 cm patches of square wave grating
 Gratings contrast : 82% - 84%
 Proper illumination :10 candelas/m²
 Measures near visual acuity and NOT distance

CATFORD DRUM TEST (CAT)
 Based on observation of Pendular Eye movements
 It comprises of white cylinder marked with black dots
of increasing size corresponding to visual acuities
 The drum is masked by a screen except for a
rectangular aperture which exposes a single spot
 Spot is made to oscillate horizontally and stimulates
eye movement
 Overestimate vision as target is moving and test is
conducted at Short working distance
 Unreliable for Amblyopia Screening

WORTH'S IVORY BALL TEST
 Based on Quality of Fixation
 Ivory balls ranging from0.5“ to 1.5", rolled on
floor at a distance of about 3 metres
 Child is asked to retrieve each ball
 Rough estimate of visual acuity is made from
the size of smallest ball which the child can see

BOECK CANDY TEST
 Child picks up only those candy beads
which he can see easily
 Beads of different sizes are shown to child
and is expected to pick them up
 This gives approximate estimation of visual
acuity

SCREENING TEST FOR YOUNG
CHILDREN & RETARDS [STYCAR]
 DYNAMIC
• Based on Pursuit Eye movements
• Ten Balls rolled across a well illuminating contrasting
floor 3 m away from child
• Pursuit Eye movements indicate that balls are seen
 STATIC
• The sphere is mounted on a wand and introduced
into the periphery of the visual field and examiner
determines whether the child fixates or not

MARBLE GAME TEST
 In children of 1-2 years of age reaching or
placing games can be used to estimate visual
function
 This test is not intended to measure visual
acuity of each eye
 The child is asked to place marbles in the
holes of a card or in a box
 Compare the functioning of the child’s eye
when one or the other is closed
 The vision of an eye is then noted as being
useful or less useful

DOT VISUAL ACUITY TEST
 Child is shown an illuminated box with black
dots of different sizes printed on it
 The smallest dot identified denotes the
visual acuity of the child
 Test distance is 25 cm
 VA : 20/800 to 20/20

CARDIFF ACUITY TEST (CAT)
 Principle : vanishing optotype
 Target : pictures, of the same overall size,
drawn in decreasing widths of white space
 Acuity is determined by the narrowest white
band for which the target is visible to the child
 Child naturally prefers to look at a target
figure rather than the blank end of the stimulus

MINIATURE TOY TEST
 Was previously used for handicapped children
and low Intelligence patient
 Component of STYCAR Test
 2 sets of Miniature object are used; 01 set is
with examiner standing at 10 ft and child is asked
to pick up similar objects from his own set

COIN TEST
 Coins of different sizes are shown to child and
expected to pick them up
 Child picks up only those coins which he can
see easily

PATTI PICS
 Patti Pics were introduced in 2003 as an improved
test for vision screening and testing of pediatric
patients where universal symbols and matching may
serve the process better than letters or other symbols.
 Only symbol test with the stated objective of
calibration targeted to equal Sloan letters used in the
ETDRS charts
 This uniformity is especially important when taking
patients from symbols to letter tests

LANDOLT’S BROKEN RING CHART
 Based on Minimum Separable distance
 The rings are constructed on the same basis as
that of Snellen’s test
 Child is instructed to indicate by the motion of
the hand at which point each one is broken
 Interpretation of the last line identified by the
child determines visual acuity

BROKEN WHEEL TEST
 Consist of 8 pair of test cards 20/20, 20/25, 20/30,
20/40, 20/60, 20/80, 20/100, 20/120.
 Each card has a black line drawing of a car on a
white background
 1 with solid wheels, other with broken wheels.
 Done from 3 m distance

TUMBLING E TEST
 Based on Minimum Separable distance
 Task is to identify the direction in which the limb
of E points
 Identification of the last line gives visual acuity

ISOLATED HAND FIGURE TEST
 Sjogren has replaced the E chart with the isolated
figure of a hand & in some children it works better than E
chart

SHERIDAN LETTER TEST
 It uses 5 letters H O T V X
 A and U are added in 7 letter set
 Examiner shows cards having small range of
letters at 3 m and child points at one of the card
identical to the examiner card

LIPPMANS HOTV TEST
 Simpler version of Sheridan's test using only 4
letters HOTV
 Test distance 3 m

ALLEN’S PICTURE CARDS
 It is recorded same as Snellen’s acuity test,
instead of letters child identifies picture at a
distance of 6m

KAY PICTURE TEST
 Gold Standard vision test for pre-literate children,
providing accurate, crowded visual acuity
measurements earlier than symbol and letter tests.
 The test is done at distance of 6 meter
 Spiral booklets with a single picture in each page
 The size decreases from 6/60 to 6/6 with each
size having 3 cards
 Again the patient is given a key card and is
asked to match with the picture as shown in the
main chart

LEA SYMBOL TEST
 Good for amblyopic patient to avoid crowding
Phenomenon

LIGHT HOME PICTURE CARD
 A chart containing an apple, a house and an umbrella
arranged in Snellen’s equivalents of 20/200 - 20/10
 The child identifes the pictures along the lines
 The test is carried out at 3m
 12 cards are available, size of each card is 4×5 inch

VISION TEST IN 5-6 YEARS AND
ABOVE

SNELLEN’S VISUAL ACUITY TEST
 Most commonly used
 Smallest Object which can be resolved by the
eye subtends the same visual angle at the nodal
point of the eye i.e. 5 min of arc
 Testing distance is 6m

LOGMAR VISUAL ACUITY CHARTS
 Based on Minimum Angle of Resolution
 Same number of letters on every line
 Have regular progression in the size and spacing
of the letters from one line to next
 More Precise than Snellen’s Test

ETDRS
 The ETDRS acuity test was developed to aid
in evaluating the changes in vision following
panretinal photocoagulation in patients with
diabetic retinopathy. Previous studies had
somewhat confusing results due to
inadequacies of the acuity tests used in those
early studies.

CONCLUSION
 Measuring vision in children is a comprehensive
task. For diagnostic purposes, follow-up and
evaluation of visual impairments, all elements
should be considered and compared with the
visual function of daily life. Results need to be
explained and discussed with the parents or
guardian to help them understand the situation
and strengthen interaction with their children. This
will reduce the visual disability, especially if the
vision cannot be improved through medical
treatment.

Visual acuity in children

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