ASSESMENT OF VISUAL ACUITY IN CHILDREN

Intern:- Kavita ChoudharyModerator :- Kunal Kishor

DefinitionIt is defined as the resolving power of the eye or

ability to see two separate objects.It is determined by the smallest retinal image which

can be appreciated at a certain distance.The VA test measures the smallest letters that

patient can read on a standardized chart at a distance of 6m / 20 feets

PrincipalThe two distinct points can only be

recognizable as separate when they subtend an angle of 1minute of an arc at the nodal point of the eye

Normal visual Developments

AGE

At birth 6/120

4 months 6/60

6 months 6/36

1 year 6/18

2 years 6/6

Expected visual acuity 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

Vision Tests in InfantsVision Tests in Infants

CSM method

C : CentralS : SteadyM : Maintenance

2.Preferential Looking TestMost Commonly used TestBased upon turning of the head or eyes towards the

pattern rather than a uniform [homogenous] field.Alternating Black and White Stripes are presentStripe width progressively narrows which is then

randomly shown next to plain test objectChildren with better vision are able to see finer

grating and turn towards it

Drawbacks of Preferential Looking Tests

Test near vision not distance vision

3.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

Drawbacks

Measures near visual acuity and not distance Measures resolution acuity

4.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

Abnormal VEP may indicate a problem with the visual information reaching the cortex

VEP is very sensitive to optical blurring, can thus be used as a method of refraction in very young patient

VEP

VEP is useful in the determination of problems such as amblyopia, cortical blindness, and visual impairment

5.Opto kinetic nystagmusCommonly used Test in NeonatesTest object moves in one directionBased on observation of Pendular Eye

movementsSlow following phase & rapid recovery

phase.Good correlation with subjective acuity.

Drawbacks of Optokinetic Nystagmus

Overestimates the visual acuity as the target is moving

6.Catford Drum testBased on observation of Pendular Eye movementsTesting distance is 60 cmIt 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

Draw backs

Overestimate vision as target is moving and test is conducted at short working distance

Unreliable for Amblyopia Screening

Testing Of Uniocular Amblyopia In Infants

Occluding Amblyopic eye child does not resist.while occluding the normal eye, child resists

the occlusion.

Vision test in 1-2 years

1.Worth's ivory ball test:

Commonly UsedBased on Quality of FixationIvory balls ranging from 0.5" to 1.5" ,

rolled on floor at a distance of about 3 metres.

Child is asked to retrieve each ballRough estimate of visual acuity is made

from the size of smallest ball which the child can see

2.Boeck Candy TestChild picks up only those candy beads which

he can see easilyBeads of different sizes are shown to child and

is expected to pick them upThis gives approximate estimation of visual

acuity

3.Screening Test for Young Children and Retards [STYCAR]

Based on Pursuit Eye movementsTen Balls rolled across a well illuminating

contrasting floor 3m away from childPursuit Eye movements indicate that they are

seen

Vision Test in 2-3 years

1.Cardiff Acuity TestPrinciple: 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.

2.Miniature Toy TestWas previously used for

Handicapped children and low Intellegence patient

Component of STYCAR Test2 sets of Miniature object are usedOne set is with Examiner standing at

10ft and child is asked to pickup similar objects from his own set

3.Coin TestCoins of different sizes are shown to child and is

Child picks up only those coins which he can see easily

expected to pick them up

4.LEA Symbol test

Used in children age between 2-Good for amblyopic patient to avoid crowding

phenomenon.

Vision test in 3-5 years

1.Allen’s Picture CardsIt is recorded same as Snellens Acuity testInstead of letters child identifies picture at a

distance of 6m.

2.Sheridan letter testIt uses 5 letters HOTV & XA&U are added in 7 letter setExaminer shows cards having

small range of letters at 3mChild points at one of the card

identical to the examiner card

3.Lippmans HOTV testSimpler version of Sheridan's test using only 4

letters HOTV.Test distance 3 meter

Vision Test in 5-6 Years and above

1.Snellens Visual Acuity Test

Most commonly usedSmallest Object which can be resolved by the eye

substends the same visual angle at the nodal point of the eye i.e 5 min of arc

The test employs a chart with rows of letters with diminishing size

Each row is accorded a number indicating the distance in meters at which a person with normal visual acuity should correctly identify the letters

Testing distance is 6m

2.LogMAR Visual Acuity Charts

Based on Minimum Angle of Resolution

More Precise than Snellen Test Have regular progression in the

size and spacing of the letters from one line to next

Same number of letters on every line

3.Tumbling E TestBased on Minimum Separable distanceTask is to identify the direction in which

the limb of E pointsIdentification of the last line gives visual

acuity

4.Landolt’s Broken Ring Chart

Most Commonly usedBased on Minimum Separable

distance.The rings are constructed on the same basis as

that of SnellensChild is instructed to indicate by the motion of the

hand at which point each one is brokenInterpretation of the last line identified by the

child determines visual acuity

Conclusion

Despite the development of methods appropriate to different ages, measuring acuity remains difficult in infants.

In addition, many techniques require special equipment and conditions, making them unsuitable for some settings

Cont………..

Whichever method is used to measure a child’s vision, it is important to assess vision corrected for any refractive errors, and to assess the eyes separately as well as together whenever possible

Thank You