VISUAL ACUITY IN INFANTS

Zarin khanB.Optom

VISUAL ACUITY

It is the resolving power of the eye. It is an ability to see two separate object as separate.

VISUAL ACUITY IN INFANTS Visual acuity, in preverbal

infants defined as a motor or sensory responses to a threshold stimulus of known size at known distance.

MEASUREMENT OF VISUAL ACUITY IN INFANTSA child should be aware & responsive

to the surroundings & situation.A normal pupillary response, a

positive blind response & an elicitable OKN indicate good visual acuity.

VA improves rapidly during the 1st years of life than matures approximately 5-6 years of age

Fixation behaviour can be determined accurately in this age group as the fovea develops completely by 3 months of age.

If the child habitually fixates with one eye, it indicates poor vision in the non fixating eye.

AGE GROUP Infants (Birth – 14 months)

Toddlers (14 months – 2 1/2 years)

Pre-schoolers (2 1/2 years – 5 years)

School going children (5 years – 15 years)

NORMAL VISUAL DEVELOPMENTVery soon after birth – can fix & follow

a light source.1 months – fixation is central, steady &

maintained. Can follow a slow target. 3 months – binocular vision & eye

coordination.6 months – reaches out accurately for

toys.9 months – looks for hidden toys.2 years – picture matching3 years – letter matching of single

letters.5 years – Snellen chart by matching or

naming.

DIFFERENT TYPES OF VISUAL ACUITY TEST IN INFANTS Opto kinetic nystagmus test Preferential looking test Visually evoked response Catford drum test Cardiff acuity card test Indirect assessment of visual acuity Hundred & thousand sweet test. Lea paddle

OPTO KINETIC NYSTAGMUS TEST

OKN drum has been proposed as a method of measuring visual acuity in children.

In this test, nystagmus is elicited by passing a succession of black & white stripes through the patient’s field of vision.

Procedure:Striped patterns are presented

on a rotating drum.The drum is moved in one

direction in front of the patient.If the striped pattern is visible,

the patients eyes will make ‘Rail road Nystagmus’ eye movements as they follow the movement of the stripes.

The clinician determine that elicits the nystagmus response when it is moving.

RECORDINGNew born

6/120

2 months 6/60

6 months 6/30

20-30 months 6/6

PREFERENTIAL LOOKING TESTPLT is used to assess VA in infants

& young children who are unable to identify pictures or letters.

Procedures: 1. The child is presented with

two stimulus field. 2. One with stripes and the

other with a homogenous gray area of the same average 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.

If the child can see the stripes, he/she will prefer to look them.

If the child can’t see them, the child will not show a preference.

Visual acuity determined with this method

RECORDING New born 6/240

3 months 6/60

36 months 6/6

VISUALLY EVOKED RESPONSE

It is quite useful in assessing visual function in infants.

It is a electro encephalo graphic recording made from the occipital lobe in response to visual acuity.

It is the only clinically objective technique available to assess the functional state of the visual system beyond the retinal ganglion cells.

Flash VER determines the integrity of macula & visual pathway function.

Patter VER depend on form sense & gives rough estimate of the visual acuity.

CATFORD DRUM TEST It is a detection acuity

test. It is useful in infants &

preschool children. In this test, the

children is made to observe an oscillating drum with black dots of varying sizes.

The smallest dot that evokes pendular eye movements denotes the level of visual acuity

CARDIFF ACUITY TEST The principle of the target design is that

of the vanishing optotype. The targets are pictures drawn with a

white band border by 2 black bands, all on a neutral gray background.

The examiner simply observes the children’s fixation.

INDIRECT ASSESSMENT OF VISUAL ACUITYBlink reflex in response to

sound.

Menace reflex i.e; closure of the eyes on the approach of an object if vision is normal.

BINOCULAR FIXATION PREFERANCE

Behaviour evidence of decreased vision in right eye.

A small toy is used to get the child’s attention & the examiner covers the right eye to monitor fixation of the left eye. The child fixates on the toy without objecting.

When the left eye is covered , the child objects & tries to move the examiner’s hand.

When the right eye is covered, the child does not object & tracks the object

CSM Method

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 – 6/6CSNM –6/36 – 6/60Unsteady central fixation <

6/60

HUNDRED & THOUSAND SWEET TEST

If child able to pick up small sweets at 33 cm, visual acuity is at least 6/24 or 20/80.

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 .

Lea paddle

References…

Theory and practice of optics and refraction—A.K Khurana

Clinical visual optics.

Internet.

THANK YOU……