Eyes Inspection Visual Acuity Visual Fields Pupillary Response Fundoscopic Exam.
ASSESMENT OF VISUAL ACUITY IN CHILDREN
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Transcript of ASSESMENT OF VISUAL ACUITY IN CHILDREN
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
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
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
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
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.
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.
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
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.
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
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