Multiple choice

A visual defect known as astigmatism is the result of

  1. an eyeball that is too short

  2. an eyeball that is too long

  3. an abnormal distribution of visual receptors in the retina

  4. a misshapen cornea or lens
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D Correct answer
Explanation

Astigmatism is caused by an irregular curvature of the cornea or lens, leading to distorted vision at all distances. An eyeball that is too short causes farsightedness (hyperopia), while too long causes nearsightedness (myopia). Abnormal receptor distribution would affect different aspects of vision.

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