2. What is visual acuity???
Visual acuity is the ability or power of
the eye by which object are
distinguished one from the other
It is also measure the smallest retinal
image formed at the foveal region
such can be appreciated reguarding
shape & size.
3.
4. Visual acuity charts
There are two types of visual acuity
charts
Distance vision chart
Near vision chart
5. Visual acuity tests
Different types are:
Snellen test .
Random E’s/Tumbling E chart.
Landolt’s Broken ring chart.
Optokinetic drum.
Landolt c chart .
Log MAR chart.
6. Snellen chart
Construction
Each individual subtends an angle of
5’min of arc .
Each component subtends an of
1’min of arc at the nodal point of the
eye.
In snellen a series of black capital
letter on white background arranged
in progressively & diminishing the
size.
8. Measurement of visual acuity for
distance
To measure the visual acuity the
chart and patient distance should be
6meteror 20feets.
This distance can be applicable with
3m or 10feets with the help of mirror.
9. Contd…..
All visual acuity measurement can
maintain the distance of 6m because ll
rays of light coming from infinity will start
at 6m distance .
Visual acuity always has standard notation
which starts from 6/6 to 6/60
METER: 6/6, 6/9, 6/12, 6/18, 6/24,
6/30,
6/ 36, 6/ 60 .
FOOTS: 20/20, 20/30, 20/ 40, 20/60,
10. Landolt’s broken ring chart
This is similar construction to the
snellen .
Instead of letter the broken circle are
used.
Each ring subtends an angle of 5’min
of arc.
This chart commonly used for
illeterate people by asking the gap of
broken ring
14. Measurement of visual
acuity for near
The test distance commonly used for near
distance is25 to 30cm from the eye
All near charts are printer type arranged
in decrease order
The commonly used charts are jaeger’s
chart
In jaeger’s chart the printer font size
decreases from 1st to 7th line
The order is below N36, N18 ,N12, N10,
N8, N6
15. Age group
Infants (birth-14month)
Toddlers(14month-2years)
Pre-schoolers(2year-5year)
School going children(5year-15year)