Visual-Acuity Tests

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Category: Eye.
Subcategory: Subjective tests.
Estimated cost of test: Usually no charge when part of routine eye examination.
Patient time for test: 5-10 minutes.
Reliability of test results: Good.
Available as home self-test? Yes.
Note: If you wear glasses or contact lenses, bring them to the examination.

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BEFORE THE TEST

Purpose of test:

• Evaluates distant and near vision.
• Identifies extent of nearsightedness or farsightedness.

Where is test performed?

• Almost anywhere. Test requires no special surroundings.

Who performs test?

• Technician, nurse, doctor, optician, optometrist.

Risks and precautions:

• None.

Patient preparation:

• Activity - No changes necessary.
• Diet - No changes necessary.
• Medicines - No changes necessary.
• Disrobing - None required.

THE TEST

Sensory factors:

• Feeling - Some degree of apprehension or fear is normal and should be expected. Discomfort disappears when the test is finished.
• Other senses (touch, sight, smell, hearing, taste) - Not affected.

Equipment used:

• Standardized visual chart (Snellen chart).
• E chart showing the letter E in various positions and sizes. Chart is used for younger children and people who can't read.
• Jaeger card (for close reading).
• Hand-held occluder.
• Disposable tissues or disposable eyepatches.

Description of test:

Distance acuity:

• Sit or stand 20 feet away from the chart.
• Visual acuity is reported as a fraction, such as 20/20, or the distance (in feet) from chart over distance (in feet) at which normal eye can read line.
• Both eyes are tested with and without corrective lenses.

Near acuity:

• Remove glasses.
• Cover one eye, then the other.
• Read the Jaeger card.
• Both eyes are tested with and without corrective lenses.

AFTER THE TEST

Immediate post-test care:

• None.

Activity after test:

• Abnormal results call for more sophisticated studies.
• Return to pretest activities right away.

Time before test results available:

• Immediate.

TEST RESULTS

Test values:

• Test results are determined by examiner's interpretation.

Normal values:

• For distance acuity - 20/20 (ability to read a 6m letter at 20 feet).
• For near acuity - 14/14 (ability to read symbols a person with normal vision can identify at 14 inches).

What ABNORMAL may indicate:

• People with less-than-normal visual acuity require further testing, such as refraction and a complete eye examination.

Taking these drugs may affect test results:

• None expected.

Other factors that may affect test results:

• Failure to bring your corrective lenses to the examination.
• Corrective lenses that are outdated in their degree of correction.
• Corrective lenses that were improperly prescribed.

From the Complete Guide to Medical Tests by H. Winter Griffith, M.D. © 1988 by Fisher Books; electronic rights by Medical Data Exchange.