E. Eye problems

1. Short-Sightedness

A short-sighted person sees nearby object very clearly but not distant object.

This is caused by a long eyeball such that light rays from a distant object is focused in front of the retina. This condition can be corrected by the use of a concave lens.

2. Long-Sightedness

A long-sighted person sees distant object very clearly but not near object.

This is caused by a short eyeball such that light rays from a near object is focused behind the retina. This condition can be corrected by the use of a convex lens.

3. Ageing resulting in presbyopia

An increase in age leads to a reduced ability in the eye accommodation.

This is mainly due to three reasons:

1. Lens becomes harder and less elastic.

2. Reduced tension of the suspensory ligaments.

3. Decreased activity of the ciliary muscles.

The condition whereby aged individuals lost their ability to focus on very near objects is known as presbyopia.