1. VISUAL ACUITY MEASUREMENT
IN
PEDIATRICS
Hira Nath Dahal

2. PRESENTATION LAYOUT
• Introduction to Visual acuity and its types
• Visual development
• Normal visual response
• Different methods of visual acuity assessment
• Visual acuity assessment in
• Non & Preverbal children
• Verbal children
• Conclusion

3. VISUAL ACUITY
• measure of the spatial resolution of the visual processing
system
• Expresses the angular size of the detail that can just be
resolved by the observer
• Visual acuity testing is a clinical procedure to access the
ability of an individual to discriminate detail and distinguish
form.

4. • Four types of Visual Acuity
• Detection acuity: estimates the minimum size
visible i.e. the actual presence or absence of
target is determined e.g. Catford drum, stycar balls
• Resolution acuity: minimum separation which
allows discrimination i.e. the minimum
separation detected between the elements
of gratings or checkerboard is determined
e.g. preferential looking charts, Lea gratings

5. • Recognition acuity: the minimum size, which
facilitates identification i.e. the letters or
pictures or orientation of symbols are
identified e.g. letters or pictures
• Localization acuity (Vernier Acuity): estimates
ability to distinguish when two lines placed
end-to-end is displaced laterally i.e. the
differences in spatial position of a test target is
determined

6. • Normal development of visual function
starts with the detection acuity acquired at
birth
undergoes a rapid development into
higher acuity function such as
resolution, developing later on.
• There are many techniques of visual acuity
assessment available to quantify the
different level of visual function

7. • Each visual acuity function requires different level
of cortical functioning, therefore may result in
different acuity measurements for given
individual, if measured by different techniques.
• In a child, level of recognition, resolution and
detection acuities differ; with recognition acuity
measured lower than resolution, which is still lower
than detection acuity.
Detection acuity of same value is not equal to other
forms of acuities; similarly the same value of resolution
acuity is not equal to the recognition acuity.

8. WHY TO ASSESS VISUAL
ACUITY ??
• Normal acuity in infants and young children can help
the clinician r/o a no. of disorders, including significant
refractive error, amblyopia, and ocular disease.
• VA is routinely utilized to initially set the direction for rest
of the examination. For e.g. a unilateral reduction in
visual acuity should alert a clinician for different
problems including optical disturbances, optic nerve or
chiasmal lesion, optic neuropathy, macular disorders or
functional amblyopia.
• To know if visual development is normal.
• Helps to decide eligibility for low vision and
rehabilitation services.

10. In order for visual system to develop normally,
several components are required such as
• Normal anatomical structures
• Two eyes must be positioned correctly and have
clear media.
• Neurological connections of visual pathway to
visual cortex must also be functional.

11. • Visual acuity improves rapidly during the first year of
life and then matures more gradually to adult levels
at approximately 5-6 years of age.
• Structural development is largely completed by 2-3
yrs. of life but functional changes continues
throughout life.
• Although the central cones function by birth, acuity
as measured by the different techniques does not
approach 20/20 (6/6) until from 6 to 30months
(depending upon the examination technique used).

12. • Reasons for this delay include the incomplete
• development and specialization of
photoreceptors,
• immaturation of synapses in the inner retinal
layers,
• Incomplete myelination of the upper visual
pathways.
• Foveal cones do not attain adult appearance until
4 months after term birth, and visual pathway
myelination continues until 2 years of age

13. VISUAL MILESTONES :
• Very soon after birth - Can fix and follow a light
source, face or large, colourful toy.
• 1 months - Fixation is central, steady and
maintained, can follow a slow target, and
converge, preference of looking at face.
• 3 months - binocular vision and eye coordination, eyes
follow a moving light or face, responsive smile.
• 6 months - Reaches out accurately for toys.
• 9 months – look for hidden toys.

14. • 2 years - Picture matching
• 3 years - Letter matching of single letters
(e.g., Sheridan Gardiner)
• 5 years - Snellen chart by matching or naming

15. Age Reflex
Birth Blinking (to light stimulus)
1 week Vestibulo-ocular
2 weeks Small saccades
2 months Large saccades, pursuit, bifoveal
fixation, convergence
3 months Uniocular fixation
4 months Fusional vergence, sensory
fusion, stereopsis
6 months Accomodation
Other function to correlate with vision

16. DEVELOPMENT AND MATURATION OF
VISUAL ACUITY :

17. NORMAL VISUAL DEVELOPMENT
• Pupillary light reaction : 30 weeks gestation
• Blink response to visual stimuli : 2-5 months
• Fixation - 2 months
• Smooth pursuit : 6-8 weeks
• Saccades : 1-3 months

18. • Optokinetic nystagmus(OKN): Developed by 2-4 month
• Ocular Alignment : 1 month
• Foveal maturation : 4 months
• Optic nerve myelination : 7 months to 2 yrs

19. • The vision of new born is quite blurry, indistinct and
shadowy, which improves significantly over the next 6
months, by that time a child recognize face of the
mother, which further improves in another 6 months
period

20. NORMAL VISUAL RESPONSE
Age Visual response
Newborn Light perception
4-7 weeks Eye contact with mother
4-12 weeks Fixates and follows interesting bright
coloured objects
3 months Change expression smiles and cries
3-4 months Reach objects using vision
6-9 months Crawling and later walking avoiding
objects
Gwiazda et al 1980

21. VISUAL ACUITY DEVELOPMENT IN
HUMAN
• Develops & matures from birth to 6 years
• Newborn: quite a blurry vision : Indistinct & Shadowy
• Improves significantly over the next 6 months: Can
recognize the faces
• At birth VA = 6/240 (20/800)
• 1 month VA = 6/120 (20/400)
• 6 months VA = 6/30 (20/200)
• 1 year VA = 6/15 (20/50) (Gwiazda et al 1980)

22. • Marg et al 1976 estimated the resolution acuity
VA of infants by Visually evoked potential (VEP)
and preferentially looking chart as follows:
 With VEP the measured VA was: at 3 months
VA = 6/18 (20/60)
by the end of 6 months VA = 6/6 (20/20)
 With Preferential looking chart, an accurate
response by a normal child as like an adult is
possible by the age of 1 year.

23. • The different available techniques for the
assessment of visual acuity function are:
1. Detection acuity: It can be
• Non quantifiable or
• Quantifiable by eliciting voluntary visual response
• Quantifiable by eliciting involuntary visual
response

24. NON-QUANTIFIABLE DETECTION
ACUITY
It is difficult to quantify the visual acuity of children who
are non-verbal under 1 year of age.
They don't show visual response to any object or
pattern, eye care practitioner cannot quantify the VA
accurately, so we should closely explore the visual
responses expected at that age by using various
techniques appropriate

25. LIGHT, FIXATION AND FORM PERCEPTION
EVALUATION
A. Illumination: A child of 4-7 weeks has expected normal VA
of light perception. So a light stimulus (torch light,
Ophthalmoscope light) can be used to elicit the fixation reflex,
facial or postural changes or an enhanced level of alertness
when lighting is altered.
Children who don’t respond to simple illumination,
visual stimuli may be demonstrated by colorful flickering lights
(most preferably red light which is most effective)

26. B. Blink reflex: A hand colorful object is placed in front of the
child face of age 4-7 weeks, a consistent response, such as
blink reflex, closing eyes or avoidance behavior is a sign of
visual discrimination using form perception.
C. Bright coloured lights or objects: A child of 4-12 weeks can
follow and fixate the bright coloured objects(toys) or light.
Where as a child of 3-4 months will reach for the bright toys
using his hands.

27. D. Pupillary response: the presence of pupillary contraction to
light and near object indicates a visual response. But this can
give false impression in the case of cortical blindness, where
normal pupillary response is obtained.

28. E. 10 PD fixation test:
This test is an indirect technique to assess
possible difference in acuity between two eyes in infants and
preverbal children.
A 10 PD vertical prism is placed in front of one
eye, if both eyes have equal visual acuity; the child will be
switching the fixation back and forth from right to the left eye.
But if one eye only takes the fixation all the time, the non-
fixating eye indicates of having poor vision

29. QUANTIFIABLE DETECTION ACUITY BY ELICITING
VOLUNTARY VISUAL RESPONSE
• Children who cannot response verbally but active
enough to response visually to the three dimensional
acuity targets (1 to 3 years of age) are subjected to
detection acuity measurement by presenting
interesting three dimensions targets which elicit
voluntary visual response.
• Some of the techniques are:
• Ivory balls
• Use of candy beads

30. IVORY BALLS
Uses white Styrofoam spheres of various
diameters that are rolled perpendicular to the patient’s line of
sight individually along the black cloth strip.
The speed, distance and the side of roll is
varied and a record is made of the smallest sphere that the
child follows at a set of distance and corresponding acuity
levels is calculated

31. USE OF CANDY BEADS
Children of less than 3 years of age need more effective
motivator to co-operate to the practitioner during the visual
acuity assessment.
 Chocolate coated candy beads can be the best possible
option.

32.  Candy bead is placed in one hands of the practitioner
presenting both hands to the child. The visual response is
determined by observing the fixation pattern, gesture or
child’s hand reaching for the candy.
 This test is a gross acuity assessment technique because it
does not arrive to the threshold acuity value.
Approximately, 1mm bead located at 33cm represents
detection acuity of 6/60 (20/200). Also, it provides valuable
information to the practitioner that the child is able to see at
a normal working distance.

33. QUANTIFIABLE DETECTION ACUITY BY
ELICITING INVOLUNTARY VISUAL
RESPONSE
• Visual acuity in non-verbal and preverbal children who
don't response voluntarily can be obtained by using
techniques which elicit involuntary visual responses.
Few techniques are:
a. Optokinetic Nystagmus (OKN)
a. Catford drum
b. OKN drum
b. Visual Evoked Potential

34. OPTOKINETIC NYSTAGMUS
• OKN can be elicited at birth but has poor directed
saccade, which can be reasonably accurate by the age of 3
months.
• OKN is a series of repetitive eye movements, consisting of a
slow pursuit phase, during which a moving target is smoothly
tracked, followed by the fast saccade, allowing refixation
when eye meets its limit of movement in the direction of the
pursuit.
• Theoretically if an individual can visually discriminate the
series of bars movement across the visual field, as the target
gratings rotate, OKN is observed. Clinically, a Catford drum
or an OKN drum is available to measure visual acuity

35. CATFORD DRUM
Principle
• The Catford drum uses oscillating black dots on a white
ground, and is based on the principle that a child’s attention
is drawn to a moving target
• The observer can use the corresponding oscillatory eye
movement as confirmation that the child sees the target. The
oscillatory movement is generated by the pursuit system.

36. • This consists of a white drum marked around its
circumference with black dots corresponding in size to
Snellen letters if viewed from a distance of 60 cm. the size of
dots ranges from 6/60 to 6/6. each dot is displayed singly in
the rectangular aperture of the screen which covers the
other dots.
• Once the child’s cooperation has been assessed, the drum
is held at a distance of 60 cm, one eye is covered and dots
of decreasing size are exposed in the aperture until the
minimal visible has been estimated. The other eye is then
tested
• It has been shown to overestimate visual acuity by the factor
of four (Atkinson et al 1981)

37. OKN DRUM
Principle
• Strips which move across
the fields of vision elicit an
observable eye
movement, comprising a
following movement as the
subject fixates on one
stripe(pursuit) and a rapid
movement in the opposite
direction to fixate the next
stripe(saccade).
• The stripes are best presented as optical
gratings using black and white stripes of
equal width. To hold the infants attention a
large part of his field must be filled by the
stripes
• Stripes can be presented in various ways:
rotating drum or electronically generated
stripes displayed on a television screen
• An eye movement reponse indicates that a
grating can be seen, the movement can be
directly observed or more
accurately, electro-oculography can be used
to trace and record eye movement

38. Method:
• The stripes should be vertically positioned and moved
horizontally at both slow (3 stripes/s) and fast (30 stripes/s)
speeds. The slower rate stimulates the smooth pursuit and
saccadic systems, while the faster speed appears to involve
a more primitive optokinetic system
• Stripes of increasing spatial frequency are presented until a
frequency is reached which fails to elicit an optokinetic
movement. The highest spatial frequency which produces
OKN at a slow speed, is the measure of visual acuity

39. VISUAL EVOKED
POTENTIAL
• It is an electro diagnostic test that provides the fast, objective
assessment of visual function and visual acuity of infant and young
children.
• Stimuli, such as gratings or flickering checkerboard is presented
before the child, an the occipital cortical response in the form of
change in electrical activity to visual response is detected by
placing electrodes on the scalp surface, overlying the occipital
cortex.
• The cortical electrical responses are analysed in the form of wave
front and amplitude by a computer system estimating the visual
acuity. The VEP mostly measures the macular function but doesn't
estimate higher visual function. So, there exists difference between
estimated visual acuity and overall visual functioning of the child.

40. 2. RESOLUTION ACUITIES
• Resolution acuity is measured by using the preferential
looking (PL) technique in the form of Teller, Keller cards
or Lea grating cards.
• This technique determines the objective information of
visual acuity in nonverbal children. This is based on the
research that infants, when simultaneously presented
with a patterned stimulus and a homogenous field will
preferentially view the pattern stimulus.
• It involves the presentation of the two stimuli, one black
and white gratings pattern and the other unpatterned
grey field of equal size and luminance

41. • The child preference is observed by viewing the pattern
and length of fixation while subsequent presenting the
cards with higher grating frequency, till the child show
no preference
• At this time, the child is unable to discriminate the black
and white pattern and the resolution acuity is noted in
the form of cycle per degree of the highest frequency
that was preferred by the child

42. TELLER ACUITY CARDS
• A set of 16 cards is available containing a uniform grey
background on one side and other side, containing a square
on the right or left side of which is printed a square-wave
grating of known spatial frequency. The card is presented to
the patient through a rectangular grating.

43. PROCEDURE
• The child is held in front of a grey cardboard screen that
shields his or her view of the room . For infants the 38cm
testing distance is recommended, whereas the 55cm
distance is recommended for the toddlers
• To test the acuity, the examiner displays a series of
cards, each containing a black and white grating of different
spatial frequency, located to the left or right of the central
peephole
• It is best to begin with the stripe width that is wider than the
threshold predicted for the age of the infants. If it is clear that
infants see the stripes, the examiner presents the card with
the next finest stripe width.

44. CONTD…
• Testing continues until the examiner is confident
enough about he child’s responses to make a
judgement concerning the finest grating that the child
can detect.
• The spatial frequency of this grating is taken as an
estimate of that child’s visual acuity
• The results can be expressed in octaves or converted
to equivalent Snellen values, min of arc or cycles per
degree
• The testing time ranges from 6-10 min

45. • To eliminate the possibility of a side preference for a
particular child, the examiner should position the cards
so that the side with the stripes varies from right to left
on a random fashion

46. KEELER CARDS
• These cards are printed with a circular patch to avoid
identification of the grating by its edge
• They also have an ‘empty’ circle printed on the other side:
this leads to a different visual response whereby the infant
may look from one circle to the other before a definite
fixation preference is made

47. Clinical problems arise if there is :
• Nystagmus, which may make it difficult to assess when
the patient is looking towards the grating, especially if
there is a compensatory head posture. Testing in the
vertical plane can be helpful in this situation
• Large angle alternate esotropia with crossed fixation,
when it can be difficult to know to which side the child
is looking when both eyes are open
• Loss of interest and fatigue

48. LEA GRATINGS CARDS
• The test can be used at different distances and with two
different presentation techniques:
1. By lifting the grey and the striped stimulus simultaneously
in front of the child and keeping them there without moving
them.

49. 2. By hiding the striped
pattern behind the grey
surface and sliding the two
surfaces apart with the same
speed in opposite directions.
• Normally the child will follow
the movement of the striped
pattern if (s)he sees it. If the
child has problems in
seeing visual information in
motion there will be no
following movement
The result is reported as “responded to ___ cpcm grating at
a distance of ___ cm/inches”.

50. 3. RECOGNITION ACUITY
• Recognition acuity can be attempted to a child of 3 years or
more.
• The standard subjective visual acuity testing requires verbal
communication, sustained attention and concentration. So,
cannot be used with non-verbal and preverbal children and
is difficult to use with preschool children
• Even if the child doesn't give verbal communication,
matching activities can elicit useful information about
recognition acuity.
• Standard Snellen acuity chart is applicable to the children of
age 6 or more, but for the younger children various two
dimensional symbols, matching a puzzles are used in shorter
testing distance (usually 3m ) to assess the recognition acuity

51. BROKEN WHEEL TEST
• Uses a clinical approach of testing
for visual acuity by incorporating
the Landolt C.
• The Broken Wheel Acuity Test
utilizes cards that have a familiar,
non-threatening symbol (car),
presented in a forced choice
response. The simple recognition
of the gap in a Landolt Ring is the
critical feature.
• Testing distance: 3m
The acuity level in this test has been established to be
equivalent to the Snellen Letter optotype

52. PRE SCHOOL (ALLEN)
PICTURE TEST
The Allen chart includes easily recognized pictures, including a
cake, hand, bird, horse, and telephone.

53. • This test is recorded in terms of a 30-foot denominator. It is
intended for preschool children and has given reliable results
from the age of two years and up.
• Method: Pictures are shown to the seated child at close
range with both eyes open and the child is asked to give a
name to each picture. One eye is then covered and the
examiner presents the pictures in sequence while backing
away from the child. The greatest distance at which three of
the pictures are consistently recognized by each eye is then
recorded as the numerator of a 30 foot denominator .
• For e.g.
• Right eye maximum distance =15 feet / VA: 15/30
• Left eye maximum distance= 10 feet / VA: 10/30

54. KAY PICTURE TEST
• The Kay Picture Test books are all designed to
make testing young children a fun, quick and easy
process.
• Can be used quickly, easily and accurately from as
young as 18 months
• All the acuity sizes are together in one book and
there is a choice of three or four pictures at each
acuity size. This variety keeps a child interested
during the test and allows a different selection to
be shown when testing each eye in turn.

55. TESTING WITH KAY PICTURE TEST
• First, child is asked to name each picture and accept what
they say, repeating all plausible names back as confirmation.
“ cup of tea, fishy, house, welly” etc.
• then move to the correct testing distance (3 metres or 10
feet).
Don’t forget to tell the child how clever they are to know all
those pictures, then say something like “we are going to
play a game to see how clever your eyes are at seeing all
the tiny little pictures in my book”

56. • Single Kay Picture Test
• Crowded Kay Picture Test
Repeated with smaller sizes until child’s threshold acuity is reached. At
this point child is asked to name all the pictures at that acuity level plus
one size above and below if possible.

58. TUMBLING E
• For children who may be unable to perform vision testing by
letters and numbers, the tumbling E test may be used
• A chart consists of letter E in different orientations (up, down,
right and left) and sizes. Children are tested by asking what
orientation or direction the letter E is in at each letter size.

59. STYCAR LETTERS
• The letters, which are based on square, circle and
triangular shapes – the first to be recognized and
copied by young children are presented in three
groups.
• Five letters, VTOHX, for normal up to and including 3 year
olds
• Seven letters, adding A and U, for 4 year old children
• Nine letters, and L and C, for older children

60. SHERIDAN GARDINER
CHART
• This test uses the seven letters STYCAR test and key card.
The letters can be viewed singly, using flip-over cards which
range from 6/60 to 6/3
• The test is easily understood by normal 3 year olds and by
some intelligent younger children
• The number of letters is sufficient to eliminate guessing and
the test is quick and accurate

61. HOTV
• This test is similar to Sheridan-Gardiner but uses only four
letters
• This test consists of a wall chart composed only of
Hs, Os, Ts, and Vs. The child is provided a board containing
a large H, O, T, and V.

62. • The examiner points to a letter on the wall chart, and the
child points to (matches) the correct letter on the testing
board. This can be especially useful in the 3-to 5-year-old
who is unfamiliar with the alphabet.

63. F FOOK’S TEST
• This test uses the basic shapes of a square, circle and
triangle presented singly in sizes ranging from 6/60 to 6/6,
one on each face of a cube, or as a chart
• The child performs the test by picking up or pointing to a
black plastic replica of the shape he sees.

64. LEA SYMBOL
• This test consists of four optotypes (test symbols): the outlines of
an apple, a pentagon, a square, and a circle. Because these four
symbols can be named and easily identified as everyday, concrete
objects ("apple", "house", "window", and "ring"), they can be
recognized at an earlier age than abstract letters or numbers can
be
• The Lea Symbols Chart consists of lines of four different
symbols, arranged in combinations of five symbols per line. The
symbols on each line are smaller than those on the line above.

65. • The child views at distant chart and matches symbols of
different size presented on it to similar symbols on a key
cards.

66. VISUAL ACUITY ASSESSMENT
IN
NON & PRE VERBAL CHILDREN

67. 1. Tests for indirect
assessment of vision
a) Historical and
observational tests,
b) Binocular fixation
preference and fixation
targets,
c) CSM method.
2. Tests for recognition
acuity :
a) Dot visual acuity,
b) Coin test
c) Miniature toy test
d) Marble game test
e) Sheridans ball test
f) Bock’s candy test
(100’s and 1000’s test)
g) Worth ivory ball test

68. 3) Tests for resolution acuity :
a) Optokinetic nystagmus,
b) Preferential looking test,
c) Cardiff acuity cards,
d) Visual evoked potentials

69. TESTS FOR INDIRECT ASSESSMENT
OF VISION.
• Historical and observational tests
• Binocular fixation preference and fixation targets
• CSM method

70. HISTORICAL AND OBSERVATIONAL
TECHNIQUES :
• Parents or caretakers are asked routinely
whether the child responds to a silent smile,
enjoys silent mobiles, and follows objects
around the environment.

71. • Pertinent observations include
strabismus, nystagmus, persistent staring, and inattention
to objects
• For example, when a unilateral, constant strabismus is
present, visual acuity is presumed to be reduced in the
strabismic eye.
• In the presence of a constant, alternating
strabismus, visual acuity is likely to be normal in both eyes.

72. • Another behaviour that is unique to babies is “eye
popping”. Sometimes, for a variety of reasons, very
young infants don't show any distinguishable visual
behaviour 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 behaviour is
documented as "positive eye popping".

73. FIXATION TARGETS (FIX AND FOLLOW) :
• If appropriate targets are used, this reflex can be demonstrated
by about 6 weeks of age.
• The test is performed by seating the child comfortably in the
caretaker's lap. The object of visual interest, usually a bright-
coloured 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 behaviour) . 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 f/f behaviour then it is assumed that the patient
could see a small target or toy in a normally illuminated room.

74. Binocular fixation preference :
Behavioural 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.

75. Some children object to having either eye covered, simply
because they do not like having the examiner’s hand near
their face. If this is the case, this test cannot accurately
determine whether there is a difference in vision between the
eyes.

76. CSM METHOD :
• It is done with an eye fixating on an accommodative target held
at 40cm
• ‘C’ refers to the location of corneal light reflex as the patient
fixates the examiner’s light under monocular conditions. Normally
reflected light from cornea in near the centre of the cornea and it
should be positioned symmetrically in both eyes. If fixation target
is viewed eccentrically, fixation is termed uncentral.
• ‘S’ refers to steadiness of fixation on examiners light as it is held
motionless and also as it is slowly moved about.
• ‘M’ refers to the ability of the patient to maintain alignment first
with one eye, then with the other, as the opposite eye in
uncovered. Maintenance of fixation is evaluation under binocular
conditions. Inability to maintain fixation with either eye, with
opposite eye uncovered is presumptive evidence of a difference
in acuity between the two eyes.

77. Evaluation :
• CSM – 6/9 – 6/6
• CSNM –6/36 – 6/60
• Unsteady central fixation < 6/60

78. TESTS FOR RECOGNITION ACUITY
Dot visual acuity
Coin test
Miniature toy test
Marble game test
Worth ivory ball test
Bock’s candy test
Kay pictures
LEA symbols
F-fooks symbols
Sheridan Gardiner single
letter optotypes

79. • 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.
• Coin test : Child is asked to identify two faces of coins of
different size held at different distance.
• Miniature toy test :Child is shown a miniature toy from a
distance of 10 feet and asked to name / pick the pair from
assortment.

80. • Marble game test : The child is asked to place marbles in
holes of a card or in a box. It compares the functioning of
the child’s eye when one or the other is closed and vision is
noted as useful or less useful.
• Worth Ivory ball tests : Ivory balls 0.5 to 2.5" in diameter are
rolled on the floor in front of the child and he is asked to
retrieve each. Acuity is estimated on the basis of smallest
size for the test distance.
• Bock’s candy bead test : Snellen equivalent of 6/60 is
estimated by this method. The child is asked to match pick
up beads 1mm size at 40 cm.

81. Examples of recognition acuity.
A. Kay pictures
B. LEA symbols.

84. Tests for resolution acuity
Optokinetic nystagmus
Preferential looking test
Cardiff acuity cards
Visual evoked potentials

85. OPTICOKINETIC
NYSTAGMUS :
• Evaluation of the presence or absence of optokinetic
nystagmus was the first “technologic” approach to
acuity measurement in preverbal children.

86. FORCED CHOICE PREFERENTIAL
LOOKING :
• The FPL technique was conceived by David Teller.
• This testing technique is based on the observation that
infants demonstrate a greater tendency to fix a pattern
stimulus than a homogeneous field.
• They measure resolution acuity, using either a grating
target as with the Teller cards or the vanishing optotype
principle, as with the more recently Developed Cardiff
Acuity Cards.

87. • Preferential looking involves showing the infant two stimuli, a
grating composed of black and white stripes (or other
quantitated patterns), and a grey screen of equal space-
average luminance.
• An observer, unaware of the location of the patterned
stimuli, is positioned behind a peephole located centrally
between the grating and the homogeneous field.
• The observer monitors the direction of the child’s eyes and
head during stimulus presentation. The position and width of
the stripes are varied on each trial.

88. • Acuity is estimated by determining the smallest striped
width to which the infant will show differential fixation
of the grating as opposed to the homogeneous field
i.e. The frequency of the line spacing determines the
visual acuity.
• The threshold is usually defined as when the observer
is correct 75% of the time.
• This technique becomes a “forced choice” method
when the observer has to decide, based on their
observation of the child’s head and eye
movements, where the stimulus is located.

89. CARDIFF ACUITY CARD
• Each Cardiff card presents a line drawing of the object
• The picture is formed by a line that consists of a central
white line with finer black flanking lines on either side.
The luminance averaged across the black-white-black
line matches the luminance of grey background

90. • The Cardiff Test is good for slightly older children (18 -
60 months). It consists of different cards, which are held
in front of the child.
• Each has a picture in the upper or the lower part of the
card. If the child looks towards the picture on the
card, you note the size as detected.

91. • Consequently, when the line are too fine to be
individually resolved, they become indistinguishable
from the grey of the background
• The clinician determines the finest line drawing that still
attracts the child’s attention.

92. VISUAL EVOKED POTENTIAL
• Visual evoked potentials (VEPs) are electrical brain
responses that are triggered by the presentation of a visual
stimulus. VEPs are distinguished from the spontaneous
electroencephalogram (EEG) due to their consistent time of
occurrence after the presentation of the stimulus (time-
locking).
• The surface-recorded VEP reflects the activity of cortical
visual areas, with contributions from subcortical generators
being apparent only under highly specialized recording
conditions

93. • Types :
1. Flash VEPs
2. Pattern reversal VEPs
3. Sweep VEPs

94. SWEEP-VEP
• The S-VEP employs vertical stripes for testing and the
feature size is simply the width of the stripe.
• The inbuilt S-VEP program computes the acuity from the
VEP data. This represents a great advantage over other
methods such as preferential looking and the routine pattern
Visually Evoked Potentials (p-VEPs).

95. • In Sweep VEP, the spatial frequencies are varied very
quickly over time and the amplitudes are immediately
plotted with respect to spatial frequency (or time).
• For example, to measure VA, the spatial frequency
changes from low to high in about 10-20 seconds. The
regression line of the response amplitude is
extrapolated to zero, which gives a measure of the VA.

96. SELECTING THE APPROPRIATE CLINICAL
TEST :•
Because a child can vary significantly from expected age
norms, it is important not to rely solely upon chronological age
when choosing testing procedures. Appropriate test procedures
need to be based on the child's developmental age and specific
capability.
Age Suitable visual acuity test
<18 months Response to occlusion
Bock candy beads (100’s and
1000’s)
Keeler acuity cards(FPL test)
Stycar graded balls test
Cardiff acuity cards
18 mths-3yrs Keeler acuity cards
Cardiff acuity cards
Kay picture tests
Sheridan-Gardiner test

97. VISUAL ACUITY OF INFANT EYES
Test 2Months 4Months 6Months 1Year Attainment
(months)
Optokinetic
nystagmus
test
20/400 20/400 20/200 20/80 24–30
Forced
choice
preferential
looking test
20/400 20/200 20/200 20/50 18–24
Visual
evoked
response test
20/200 20/80 20/60–20/20 20/40–20/20 6–12

98. VISUAL ACUITY ASSESSMENT
IN
VERBAL CHILDREN

99. • Tumbling E chart
• HOTV chart
• Snellen’s chart
• Bailey-Lovie chart

100. SNELLEN’S CHART
• Visual acuity expresses the angular size of the
SMALLEST target that can just be resolved by the
patient
• Snellen Fraction is an expression of angular size of an
optotype at the eye
• Snellen Fraction is the most common notation of acuity
for children >5 yrs of age

101. SNELLEN’S FRACTION
VA =
Testing Distance
Distance at which letter
subtends 5 min of arc

102. BAILEY LOVIE CHART
Characteristics :
• Logarithmic size progression
• Same no. of letters at each level
• Spacing between the letters and between rows that is
proportional to the letter size
• Equal (or similar) average legibility for the optotypes at each
size level

103. • The particular visual acuity test selected by an optometrists
to assess any specific child will depend upon factors such as
test availability, age of the child and responsiveness of the
child.
• Generally once the child reaches the developmental age of 6
to 7, standard Snellen acuity charts can be utilized

104. FINALLY,
Assessment of visual acuity in Pediatrics is a Challenging
Task
• Immature Visual system
• Poor Cognitive ability
• Communication barrier
• Rapid development of visual system

105. HOW TO OVERCOME ??
• Selection of age appropriate technique
• Understanding the development of visual
system
• Accessibility/availability of VA accessories

106. RECOMMENDATIONS
• VA assessment – challenging task
• It should be given a great importance
• VA measurement should be repeated in each visit
• The best , realiable , reproducible & age appropriate
techniques should be choosen.

107. CONTD…
• Child friendly environment
• Mother’s lap is the best couch
• Interest creating surrounding
• Better to avoid VA when the child is in stress (cry, hunger)
• Don’t take VA when the child is fatigue