The eye can be compared to a photographic camera. The pupil of the eye, which can be adjusted by the iris, is comparable to the diaphagram and it serves to control the amount of light rays reaching the retina.

There are some diseases which can also occur in the eye which normal people is not knowing.
In a camera there is biconvex lens, which serves to focus the light upon a sensitive screen so that clear image can be obtained and can be visible. The light rays coming from an object in front of eye pass through the crystalline lens and are brought to focus on the retina where an image of the object is formed.

Some diseases are :- 1) blindness
2)night blindness
3)colour blindness
4)Myopia
5) Hypermetropia
6)Astigmatism