Question

what is different between nearsightedness and farsightedness

Answer 1

Nearsightedness means myopia means the person can see nearer object but can't see far distant object .It can be corrected by using concave lenses.
Far sightedness means hypermetropia means the person can see far distant object but can't see nearer object . It can be corrected by using convex lenses.

Answer 2

Near Sightedness is also known as Myopia while Far Sightedness is also known as Hypermetropia.

So, basically we need to distinguish between Myopia and Hypermetropia.

Let us first discuss about MYOPIA.

$\textbf{Myopia}$

So, when a person is suffering from Myopia, he / she can see nearby objects clearly but is unable to see distant objects distinctly. This is because, the image of the distant object gets formed in front of the retina instead of on the retina. The far point comes nearer than infinity in this defect.

The main causes of this defect are
⏺️Excessive curvature of the eye lens
⏺️Elongation of the eyeball

Myopia can be corrected by using a CONCAVE LENS of suitable power which can bring the image back on the retina.


$\textbf{Hypermetropia}$

When a person suffers from Hypermetropia, he can see distant objects clearly but is unable to see nearby objects clearly. This happens because the light rays from a closed by object focused at a point behind the retina. The near shifts farther.

The causes of this defect are
⏺️The focal length of the eye lens is too long
⏺️Eyeball has become too small

This defect can be corrected by using a convex lens of suitable power.