CBSE Class 10 Science 2020 · Paper 31/4/1 · Question 23
A person may suffer from both myopia and hypermetropia defects.
- (a)What is this condition called ?
- (b)When does it happen ?
- (c)Name the type of lens often required by the persons suffering from this defect. Draw labelled diagram of such lenses.
Answer
The condition is presbyopia, which occurs with ageing; bifocal lenses (concave above, convex below) are often required.
(a) The condition is called presbyopia.
(b) It happens with ageing, when the power of accommodation of the eye decreases due to the gradual weakening of the ciliary muscles and the diminishing flexibility of the eye lens.
(c) Such persons often require bifocal lenses: the upper portion is a concave lens (for distant vision) and the lower portion is a convex lens (for near vision), as shown in the labelled diagram.
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