Define presbiopia.

Presbyopia:

1. Presbyopia is a state of defect of vision when an individual is not able to see clearly nearby and far off objects.
2. Presbyopia is caused due to the natural ageing process of the eye.
3. The ciliary muscles lose their flexibility over time and do not work effectively, affecting the focusing power.
4. It can be treated with the use of simple eyeglasses with convex lenses or bi-focal lenses.