3. Landolt chart
(brocken circles chart)
7 raws of brocken circles { C }
The first raw can be seen by normal eye at a distance
of 60 m, next at 36 m, next at 24 m, next at 18m, next at
12 m, next at 9 m, The last raw can be seen at 6m.
5. facts
Defferentiation between 2 separate points?
when these 2 points stimulate 2 separate cones in between them
Un stimulated cone (diameter of one cone is 4 micron).
6. When 2 separate points stimulate 2 separate cones?
If the rays coming from them meet at the nodal point (15 mm in
front of the retina).
Forming a visual angel = 1 minute (1/60 degree).
facts
7. 6 m 9m 12 m 18 m
A
A
B
B
C
C
D
D
1. Rays coming from 2 points meet at the nodal point
a visual angel = 1 minute
8. Remember
The patient sits at 6 m from the chart.
test each eye separately.
.Start testing the patient from the first raw (60 m).
9. Comments
This mean the patient can see at 6 m what the normal
can see at 9 m {VA=6/9}
This mean the patient can see at 6 m what the normal
can see at 36 m {VA=6/36}
10. What do you do if the patient couldn’t see the first raw?
Now the chart at a
distance of 5 m
from the patient VA= 5/ the last raw
can be seen by
patient
11. What do you do if the patient couldn’t see the first raw from the new
distance (5 m)?
Be nearer at
4 m
And so on… till the chart is only 1 meter from the patient
The patient still can’t see
Use counting fingers
The patient still can’t see P L No PL
Patient is
blind
12. Factors affecting visual acuity
i. Degree of illumination.
ii. Degree of contrast.
iii. Error of refraction.
iv. Eye diseases.
v. Age.
