2. Definition
It 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
3. Principal
The 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
8. 2.Preferential Looking Test
Most Commonly used Test
Based upon turning of the head or eyes towards the
pattern rather than a uniform [homogenous] field.
Alternating Black and White Stripes are present
Stripe width progressively narrows which is then
randomly shown next to plain test object
Children with better vision are able to see finer
grating and turn towards it
13. 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
14. VEP
VEP is useful in the determination of problems
such as amblyopia, cortical blindness, and visual
impairment
15. 5.Opto kinetic nystagmus
Commonly used Test in Neonates
Test object moves in one direction
Based on observation of Pendular Eye
movements
Slow following phase & rapid recovery
phase.
Good correlation with subjective acuity.
17. 6.Catford Drum test
Based on observation of Pendular Eye movements
Testing distance is 60 cm
It 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
18. Draw backs
Overestimate vision as
target is moving and
test is conducted at
short working distance
Unreliable for
Amblyopia Screening
19. Testing Of Uniocular Amblyopia In
Infants
Occluding Amblyopic eye child does not resist.
while occluding the normal eye, child resists
the occlusion.
21. 1.Worth's ivory ball test:
Commonly Used
Based on Quality of Fixation
Ivory balls ranging from 0.5" to 1.5" ,
rolled on floor at a distance of about 3
metres.
Child is asked to retrieve each ball
Rough estimate of visual acuity is made
from the size of smallest ball which the
child can see
22. 2.Boeck Candy Test
Child picks up only those candy beads which
he can see easily
Beads of different sizes are shown to child and
is expected to pick them up
This gives approximate estimation of visual
acuity
23. 3.Screening Test for Young Children
and Retards [STYCAR]
Based on Pursuit Eye movements
Ten Balls rolled across a well illuminating
contrasting floor 3m away from child
Pursuit Eye movements indicate that they are
seen
25. 1.Cardiff Acuity Test
Principle: 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.
26.
27. 2.Miniature Toy Test
Was previously used for
Handicapped children and low
Intellegence patient
Component of STYCAR Test
2 sets of Miniature object are used
One set is with Examiner standing at
10ft and child is asked to pickup
similar objects from his own set
28. 3.Coin Test
Coins 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
29. 4.LEA Symbol test
Used in children age between 2-
Good for amblyopic patient to avoid crowding
phenomenon.
31. 1.Allen’s Picture Cards
It is recorded same as Snellens Acuity test
Instead of letters child identifies picture at a
distance of 6m.
32. 2.Sheridan letter test
It uses 5 letters HOTV & X
A&U are added in 7 letter set
Examiner shows cards having
small range of letters at 3m
Child points at one of the card
identical to the examiner card
35. 1.Snellens Visual Acuity Test
Most commonly used
Smallest 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
36. 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
37. 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
38. 3.Tumbling E Test
Based on Minimum Separable distance
Task is to identify the direction in which
the limb of E points
Identification of the last line gives visual
acuity
39. 4.Landolt’s Broken Ring Chart
Most Commonly used
Based on Minimum Separable
distance.
The rings are constructed on the same basis as
that of Snellens
Child is instructed to indicate by the motion of the
hand at which point each one is broken
Interpretation of the last line identified by the
child determines visual acuity
40. 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
41. 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