Question

What is presbyopia ? Write two causes of this defect. Name the type of lens which can be used to correct presbyopia .

Answer 1

Presbyopia: is a defect of vision in which person find difficult to see the nearby object as well as distinct objects clearly.

Causes

• This defect of vision arises due to the weakness of ciliary muscle in old age person.
• Due to loss of elasticity to change the focal length of a lens it causes decreasing the flexibility of eye lens.

This defect of vision corrected by using the suitable lens called " bifocal lens".in this type of lens the lower portion is a convex lens to focus close object. And the upper portion is a concave lens to focus on the far object.