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Which of the following defects is corrected by using a bi-focal lens?

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Astigmatism

Coma

Myopia

Presbyopia

answer is D.

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Detailed Solution

Presbyopia is corrected by using a bi-focal lens.
In presbyopia, the eye's near point gradually recedes away with ageing. Power of accommodation of the eye decreases. It is caused due to gradual weakening of the ciliary muscles and diminishing flexibility of the eye lens.
A bi-focal lens is used to correct presbyopia. The upper portion of a bifocal lens consists of concave for distant vision, and the lower portion consists of convex for near vision. Typically, bifocal spectacles with the appropriate focal lengths are used to rectify this problem. To view distant objects clearly, the upper portion of the lens corrects myopia. The lens's lower portion corrects hypermetropia to see items nearby clearly.

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