Define presbyopia.

Hint: We know that the human eye is a very complex part of the human body, which enables us to see things. However, due to various reasons like age, or excess use of technology or due to accidents, it loses its ability to function properly. Presbyopia is one such defect.

Complete answer:
Presbyopia is the process of losing vision due to natural aging, which weakens the contraction and relaxation of the pupil, causing it hard to focus on the objects at sight. And therefore affecting the focusing power of the eyes. However since this is a physical problem on the outside of the eyes, this can be rectified using appropriate lenses with appropriate power. Mostly convex lenses with positive power are used to rectify this issue. This is often seen in people between 40-60 age.

Additional information:
Since this defect is mostly seen in old age, there are chances that myopia or short-sightedness coexist with presbyopia, in such cases cylindrical lenses are used.
If the nerve connecting the eyes and the brains is affected due to age or accident, this causes no vision or a situation called blind, where the person loses his ability to perceive light information.

Note:
Presbyopia is a vision defect which occurs due to aging. This can show up in any person regardless of his or her history of eye health. This cannot be avoided, but it can be delayed by taking proper care of eyes and consuming vitamin A on a regular basis, from a very young age.