Visual acuity in infants

Visual acuity in infants
Farhana Adnin
B.optom,4th batch
ICO,CU .

VISUAL ACUITY…?
Resolving power of the eye or the
ability to see two separate objects
as separate.

Visual acuity in infants..???
 Visual acuity, in preverbal infants, is defined as a
motor or sensory response to a threshold
stimulus of known size at known testing distance.

Development & maturation of
visual acuity…..
 To receive visual stimulation the anatomical
structures must be present, the two eyes must be
positioned correctly and have clear media.
 The neurological connections of the visual
pathway to the visual cortex must also be
functional.

 Compared with the relatively dark environment within the
uterus, the newborn is familiar to visual stimuli of differing light
intensity and contours within the first few months of life. This
encourages the development of the lateral geniculate nucleus
and striate cortex.
 Structural development is largely complete by 2-3 yrs of life
but functional changes continues throughout life.

VISUAL MILESTONES..
 Very soon after birth - Can fix and follow a light source, face or
large, colorful 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 cordination, eyes follow a
moving light or face, responsive smile.
 6 months - Reaches out accurately for toys.
 9 months – look for hidden toys.
 2 years - Picture matching
 3 years - Letter matching of single letters (e.g., Sheridan Gardiner)
 5 years - Snellen chart by matching or naming

Measurement of visual acuity..in infants
 A normal pupillary response,elicitable OKN indicate good
fixation visual acuity.
 Fixation behaviour can be determined accurately in infants
as fovea develops completely by 3 months of age.
 OKN remains asymmetric till 4months of age,it’s a gross
visual assessment.
 VER helpful in establishing the presence of cortical
blindness & give an estimation of visual acuity.
 Forced choice preference gives optimum response at 3-12
months.

Types…
 There are at least two types of visual acuity
recognition acuity and
resolution acuity.
 Recognition acuity relates to the detail in the smallest
letter, number or other shape that can be recognised
 Resolution acuity is the smallest separation between
dots or between bars in a grating that can be resolved.
 Discrimination of 2 spatially separated targets.(for infants)

Visual acuity tests for infants…
Tests for indirect assessment of vision
a) Historical and observational tests
b) Ability to follow target
c) Binocular fixation pattern
d) CSM method.
Tests for resolution acuity
 Optokinetic nystagmus test(OKN)
 Preferential looking test(PLT)
 Visually evoked response(VER)
 Catford drum test.
 Cardiff acuity card test.

….
Tests for indirect assessment of
vision

HISTORICAL AND
OBSERVATIONAL TECHNIQUES
 Parents or caretakers are asked routinely whether
the child responds to a silent smile and follows
objects around the environment.
 Observations include
strabismus,nystagmus,persistent staring &
inattention to object.

Cont..
 Response to light- infant will blink in response to
bright light
 Pupillary response-presence of pupillary light
response indicates intact afferent visual neurological
pathways.

“eye popping.”
 Sometimes, for a variety of reasons, 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".

Ability to follow target..
 Most common .
 is a test to check there ability to look at & follow an
object or toy…

Binocular fixation pattern
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.

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.

CSM METHOD
(central steady maintenance)
 Done with one eye fixating on an accommodative
target held at 40 cm.
 ‘C’ refers to the location of corneal light reflex
fixates the examiner light at monocular
conditions.
 Normally reflected light from cornea in near the
centre of cornea and it should be positioned
symmetrically in both eyes.
 If fixation target is viewed eccentrically, fixation is
termed uncentral.

 ‘S’ refers to the steadiness of fixation at examiners light
and also as it slowly moved about.
 ‘M’ refers to the ability of the patient to maintain
alignment first with one eye then the other as the
opposite eye is uncovered.
Evaluation :
 CSM – 6/9 – 6/6
 CSNM –6/36 – 6/60
 Unsteady central fixation < 6/60

…
Tests for resolution acuity

Optokinetic nystagmus
 It is a gross test and is based on preferential
looking principle .
 It consists of a drum which has alternate black
and white strips .
 The drum is passed through patient field of
vision by rotating the drum and the eye
movement of the patient is seen

 It is done with both eye open .
 The child makes nystagmus movements if the stripes
are seen as the drum is rotated for these the patient
should fixate the eye on the drum .
 Black and white stripes are used because it gives
contrast .
 suppose once the patient has fixated his eye on one
black strip, immediately at a certain standard distance
he see second black strip and in these way constant
eye movements are seen

Advantage
 As the testing drums are reasonably priced,
portable, and rarely break, this technique
remains in use as a quick and easy method
with which to evaluate infant acuity.
Disadvantage
 The vision we get is only the approximate
value and we cant relay on it

FORCED CHOICE
PREFERENTIAL LOOKING
 First described by Fantz
 He found-infants prefer to fixate high contrast,bold
stripes, rather than homogenous fields of light.
 Monocularly done
 Teller cards used
 Range-approximately6/240 in newborns to 6/60 at
3months,& 6/6 at 36 months of age.

Procedure..
1.The child is presented
with two stimulus field.
2.One with stipes and the
other with a homogenous
gray area of the same avarage
luminance as stripes randomly
alternated.
3.Typically,infants and children
will look at the more interesting
stripes
4.A small peephole is centered
between the two fields, for observer.
5.Observer judges the location of
the strips based on the child’s head
& eye movements.

VISUAL EVOKED POTENTIALS
 Refers to electroencephalographic(EEG) recording
made from the occipital lobe in response to visual
stimuli.
 Objective technique to assess functional state of
visual system beyond the retinal ganglion cells.
 Types :
1. Flash VEPs
2. Pattern reversal VEPs
3. Sweep VEPs

Procedure :
 A headband with integrated electrodes is used for recordings
 The headband aligned the occiputal , the mid-forehead and the
temple
 Infants are positioned on a parent’s lap at a measured distance of
57 cm from a 17-inch (43-cm) display monitor, so that the
stimulus subtended a total visual angle of 20o.
 The room is darkened except for the light from the testing
equipment.
 Testing is performed monocularly, using an adhesive occluder
over the fellow eye.

…
 Flash VEP-tells about the integrity of the macular & visual
pathway.
 Pattern reversal VEP-recorded using some patterned
stimulus in the check board.In it the pattern of stimulus is
changed (black~white…white~black), but the overall
illumination remains the same.
 Sweep VEP- Sweep VEP essentially performs the same
operation, but the spatial frequencies are varied very
quickly over time . For example, to measure VA, the spatial
frequency changes from low to high in about 10-20 seconds.

The Cardiff Test
 For 0-1 year infant
 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, examiner note the size as detected.
 In Cardiff Acuity Card , the targets are pictures drawn
with a white band bordered by two black bands, all on a
neutral grey background.

 If the child’s vision is good
enough to resolve the white and
black bands, the picture will be
visible but if the bands are too
narrow for the child to resolve
them, the picture merges with
the grey background, and simply
becomes invisible.
(vanishing optotypes)

Lea paddle
 It is based on preferential looking and snellen principle .
 The chart is placed at a distance of 1m from the patient .
 It is usually used for the age group of 3 to 9 mths .
 There are cards available of various thickness of lines .

 At a time two cards are held infront of the patient .The
blank infront and the one with lines ie, held behind it .
 Then immediately the second card is flipped out and we
keep on changing the positions.
 The patient should appreciate the card with lines .
 The test is done at same eye level and the eye
movement of patient is seen .

References
 THEORY AND PRACTICE OF OPTICS &
REFRACTION…A.K.KHURANA
 CLINICAL PROCEDURE OF OPTOMETRY
 INTERNET

Visual acuity in infants

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Visual acuity in infants