Farhana Adnin

B.optom,4th batch

ICO,CU .

Visual acuity in infants

VISION…….?

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,boldstripes, 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 avarageluminance as stripes randomly alternated.

3.Typically,infants and childrenwill look at the more interestingstripes

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 occluderover 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.

Catford Drum

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

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