Sangeetha Pulapaka

Let me tell you what I learnt a while back, when I taught physics to 10th graders.

You must have studied refraction of light, through lens The human eye also has a lens. We see objects because light is scattered from them falls on the eye.

The eye ball is spherical in shape. The front portion is more sharly curved and is covered by a protective membrane called the cornea. It is this portion which is visible from the outside. Behind the cornea, there is a place filled with  liquid called aqueous humor and behind this we have a crystalline lens which is responsible for the image formation.

Some cannot see far by objects but can see near objects clearly. This defect of vision iis called Myopia. It is also called 'near sightedness' For these people the maximum focal length is less than 25 cm. In such cases, the rays coming from different objects In such cases the rays coming from different objects after refraction through the eye lens, forms an image before the retina.

A healthy person can see objects more than 25 cm clearly.

Here is more on focal point and focal length.