Explain the internal structure of human eye. Also discuss the functions of various parts of the eye.

Human eye is roughly spherical in shape. It has a white coloured tough outer coat. It protects the interior of the eye from any damage. Its transparent front part is called cornea. In the cornea, there is a small opening called the pupil. The size of the pupil is controlled by the iris. The iris is the coloured part of eye. The iris acts as a shutter or a diaphragm to control the amount of light entering into the eye. Behind the pupil is a convex lens which focuses light on the back of the eye on a layer called retina. Retina contains several nerve cells. Sensations felt by the nerve cells are then transmitted to the brain through the optic nerve.