Practice Quiz

Ophthalmic Assistant

Category - Visual Assessment

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The distance of 20 feet is used in visual acuity tests because it represents
  1. normal vision.
  2. a safe distance.
  3. optical infinity.
  4. optical perfection.
Explanation
Answer: C - optical infinity.

The distance of 20 feet is used in visual acuity tests because it represents optical infinity. Optical infinity is the region from which a point on an object sends rays of light that are considered to be parallel onto an optical system. Consequently, it forms a clear image in the focal plane of that system.
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