explain the hole structure and function of eye with it's parts and diagram
Answers
THE HUMAN EYE
The human eye is spherical in shape with a diameter 2.5 cm.Light enters the eye through a curved front surface. This is known as cornea of the eye.It is whitish in colour. It's main function is to act as a protective layer for the eye. The space behind it is filled with a liquid called acqueous humor. Behind, the cornea is a dark coloured muscular diaphragm called the iris. The iris may be pigmented and is responsible for the characteristic colour of the eye of a person.
A small circular aperture is present in the centre of the iris. The size of the aperture is variable and self-adjustable. This aperture is known as pupil. The pupil appears black as no light is reflected from it. The iris regulates the amount of the light entering the eye by adjusting size of pupil. In dim light, the pupil, gets enlarged and thus, let's more light into the eye. In the bright light, the pupil contracts. It is this self-adjusting of the size of the pupil that not only protects the interior of the eye from excessive brightness but also improves it image forming ability.
The light entering the eye is focused by the eye lens. The eye lens is a convex lens made up of transparent crystalline layers. It is harder at its middle and gradually becomes softer towards its edges. The eye lens is held in its position by ciliary muscles. These muscles help I'm changing the curvature and hence, the focal length, of the eye lens.
The lens of the eyes forms a real, inverted image of the object on, the inner coat of the eye. This screen of eye is called retina. It is a light sensitive screen. It is a delicate membrane having enormous number of light sensitive cells or photoreceptors. These light sensitive cells are rod-shaped and cone-shaped.
The rods and cones respond, respectively, to the amount of light energy and to the colour present in it. The rods are responsible for the vision in dim conditions and the cones help us in colour vision. The cones get activated only in bright light conditions