Working of human eye

Structure of Human Eye:

The human eye is a spherical structure which fits in the eye socket in the skull bone. There are following main parts in the human eye.

• Pupil: Pupil is the round black spot in front of eye. It regulates the amount of light entering the eyes. Pupil works like aperture of a camera. In case of dim light pupil dilate to allow more light to enter the eyes. In case of strong light pupil constrict allowing less light to enter.
• Irish: Irish is made of muscles. They control the size of opening of pupil.
• Lens: Lens lies just behind the pupil. Lens becomes thin to increase its focal length. This enables us to see distant objects clearly. To focus on nearer objects, lens becomes thick to decrease its focal length. But there is a limit. The minimum distance of clear vision is 25 cm. Below this distance, we cannot see things clearly.
• Retina: Retina works like a screen or camera film. Retina is full of light and colour sensitive cells. These cells, upon receiving image send electrical signals to the brain, which processes these information to make a mental image of what we see. The photoreceptor cells in the eye are of two types, viz. rod cells and cone cells. The rod cells are sensitive to dim light. The cone cells are sensitive to bright light and colour.