Assertion (A) : Astigmatism is due to uneven curvature of lens.
Reason (R ) : It is treated with cylindrical lenses.

Options

A. If both assertion and reason are true reason is the correct explanation of assertion
B. If both assertion and reason are true but reason is not the correct explanation of assertion
C. If assertion is true but reason is false
D. If both assertion and reason are false.

Answer

B

Explanation

Both assertion and reason are true and reason is not the correct explanation of asseration
Astigmation is a defect of vison in which the image of an object is distorted , usually in either the vertical or the horizontal axis, because not all the light rays come of a focus on the retina. Some parts of the object may be in focus by light from other parts may be focused in front of or behind the retina. This is usually due to abnormal curvature of the cornea and/or lens whose surface resembles part of sphere. The defect can be corrected by wearing cylindrical lenses, which produces exactly the opposite degree of distortion and thus cancel out the distortion caused by the eye itself.