Visual acuity

1. Visual Acuity
By :
Ritwan Bin Tapeng
MA Berpengalaman
Sept/12

2. DEFINITON
•The resolving power of the eye used to
assess and quantify the eye’s ability to
resolve varying letter sizes
•Visual acuity is dependent on:
–The refractive error of the eye
–The health and the integrity of the eye
–The test targets used
–The test conditions

3. •The measurement of VA is done to monitor change in vision
with disease progression of disease and/or treatment plan
•It is a way to measure “blur” vision
•Visual acuity must be measured on every patient at every
visit!
Measurement

4. •Distance visual acuity (DVA)
•20ft or 6M is equivalent to optical infinity
•Near visual acuity (NVA)
•40cm
Standard Test Distances

5. Optotypes for measuring visual
acuity
In a clinical practice it is common to
use Optotype cards
An optotype card is formed by rows of optotypes
of progressively smaller sizes.
They are designed to be presented at a fixed
distance and on one side they usually show the
visual acuity value belonging to each row.

6. Optotypes for measuring visual
acuity
Optotype cards
Letter Cards
Snellen

7. Optotypes for measuring visual
acuity
Optotype Cards
Letter Cards
Bailey-Lovie

8. Optotype Cards
Letter Cards
Optotype Projectors
Optotypes for measuring visual
acuity

9. Optotype Cards
Number Cards
Optotype Projectors
Optotypes for measuring visual
acuity

10. Optotypes for measuring visual
acuity
Optotype Cards
One Character Optotype Cards
Landolt Rings

11. Optotypes for measuring visual
acuity
Optotype Cards
One Character Optotype Cards
Snellen “E”

12. Optotypes for measuring visual
acuity
Optotype Cards
Other Cards
Infant Visual Acuity

13. Factors that affect Visual Acuity
 Refractive error
 Size of the pupil
 Illumination
 Time exposure of target
 Area of retina stimulated
 State of adaptation of the eye
 Eye movements