Question

What is the scientific name of (a) short-sightedness, long-sightedness?

Answer 1

A human eye may suffer from a number of defects. The most common of these are
1. Short-sightedness
2. Long-sightedness
3. Loss of accommodative power
4. Astigmatism.
All these defects may be removed by the use of proper spectacles.

Complete step by step answer:
Clear sight of the eye is very essential for any human being but with the growth of human beings, eyesight gets affected by the surroundings and is called detected.
These detects are describe as follow
i) Short sightedness (Myopia): The scientific name of short-sightedness is “Myopia”. When a person is affected by myopia, he can see near objects clearly, but distant objects appear blurred. There may be two reasons for this defect.
- The eyeball is too long, so that the retina is at an abnormally large distance from the cornea.
- The eye lens is too convex, i.e. too powerful.
We can easily understand it with the help of diagram-

In this case the parallel rays coming from distant objects are focused at a point $C$ in front of the retina. And so the object appears blurred. The far point $F$ of the short-sighted person is no longer at infinity, but at some nearest point.

ii) Long-sightedness (Hyperopia): The scientific name of long-sightedness is “Hyperopia”. A long-sighted person can see distant objects clearly (by using power of accommodation), but objects closer to the eye appear blurred. and his near point is more than $25cm$ away.

Note:
- The remedy of Myopia is to wear a concave spectacle lens so that the rays starting from an object at infinity, after refraction through this lens, may appear to come from the far point of the eye.
- In the case of a hyperopia person should wear a convex spectacle lens so that the diverging ray will not diverge and be reduced which can be focused on the retina $R$ by the eye lens.
- Human eyes get affected by many defects as the age of a person increases. As “Presbyopia” and “Astigmatism”.