(C) Presbyopia
This defect arises due to the gradual weakening of the ciliary muscles and diminishing flexibility of the eye lens, usually occurring with ageing.
Source: Chapter 10, Section 10.2(c) – Presbyopia
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The key phrase in the question — "gradual weakening of ciliary muscles and diminishing flexibility of eye lens" — is the textbook definition of Presbyopia. Myopia is caused by excessive curvature of the lens or elongation of the eyeball; Hypermetropia is caused by too long a focal length or a small eyeball. For a 1-mark MCQ, simply stating (C) Presbyopia with a one-line reason is sufficient.