Visual acuity is the cornerstone of the ophthalmic examination. It measures central, or foveal, vision. Technique is important. Here is how to do a distance visual acuity test.
If you cannot test visual acuity at distance, here is how to perform near vision testing.
If visual acuity is subnormal, use the to find out if the problem is an uncorrected refractive error or a media opacity such as a cataract. Here is how to do a pinhole visual acuity test.
If a patient cannot see the largest letter on the Snellen chart of card, measure acuity by one of these methods, listed in order of decreasing visual function:
- Counting fingers
the patient can count fingers displayed between 1 and 5 feet away from the eyes.
- Hand movements
the patient can distinguish horizontal from vertical hand motions at 1 foot.
- Light perception
the patient can tell if a bright light is shined directly into the eye.
- No light perception
the patient cannot tell if a bright light is shined into the eye.
|NORMAL LIMITS OF VISUAL ACUITY BY AGE
|6 months to 3 years
||Ability to fix and follow face, toy or light.
|3 to 5 years
||20/40 or better; 1 line acuity difference between eyes.
|Older than 5 years
||20/25 or better; no acuity difference between eyes.
When the patient is illiterate, you must use other test symbols such as Tumbling E's visual acuity test or picture visual acuity test.