The defect of the eye lens which occurs when the ciliary muscles are weak is

1. Analyze the question The question asks which eye defect is caused by weak ciliary muscles. The ciliary muscles change the shape (thickness) of the eye lens so that we can focus on objects at different distances. This is called accommodation.

2. Explain the concept

• Spherical aberration: a defect of lenses and mirrors in which rays at the edges focus at different points from rays near the centre. It is not a ciliary muscle problem.
• Astigmatism: the cornea or lens is unevenly curved, so lines in one direction are blurred while lines in another direction stay sharp.
• Myopia (short-sightedness): the eyeball is too long, or the lens is too strong. Distant objects focus in front of the retina. It is corrected with a diverging (concave) lens.
• Presbyopia: the ciliary muscles weaken and the lens loses its flexibility with age. The eye can no longer accommodate for near objects, so close objects look blurred. It is corrected with a converging (convex) lens, often reading glasses or bifocals.

3. Solution Weak ciliary muscles mean the lens cannot thicken enough to focus on near objects. This failure of accommodation is the defect called presbyopia. It is common in older people, which is why many adults start using reading glasses in their 40s and 50s.

4. Answer The correct option is C. Presbyopia.

5. Exam tip Link the word to the cause:

• Presbyopia: "Presby" means old age, so think "old eyes" and weak ciliary muscles.
• Myopia: "My" gives "near is clear", so it is short-sighted and needs a concave lens.
• Hypermetropia: long-sighted, needs a convex lens.
• Astigmatism: uneven curvature, needs a cylindrical lens.