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What does the Snellen eye chart exam test?

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The Snellen eye chart examination tests visual acuity, based on the smallest letters a person can read on the chart when positioned 20 feet away from it, according to MedlinePlus. A 20/20 test result is normal. Eyeglasses or contact lenses can correct abnormal results.

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Testing with the Snellen eye chart helps reveal visual problems and symptoms of medical conditions that may require other diagnostic tools, explains MedlinePlus. A patient takes the test with both eyes open, covers one at a time, and reads the lines on the chart aloud. Patients who wear corrective lenses take the test with and without their lenses. A 20/40 result means that the line a patient reads at 20 feet away can be read by a person with normal vision from 40 feet away.

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