Q.9 Explain the disorders of Eye.

Q.9 Explain the disorders of Eye.
Following are the disorders of eye.
1. Night Blindness
Rods contain a pigment called rhodopsin. When light falls on rhodopsin, it breaks for generating a nerve impulse. In the absence of light, the breakdown products are again converted into rhodopsin. Body synthesizes rhodopsin from vitamin A and that is why the deficiency of vitamin A causes poor night vision. This problem is called night blindness.
2. Colour Blindness
Cones contain a pigment known as iodopsin. There are three main types of cones and each type has a specific iodopsin. Each type of cone recognizes one of the three primary colours i.e. blue, green and red. If any type of the cones is not working well, it becomes difficult to recognize that colour. Such person is not able to distinguish different colours, This disease is called colour blindness and is a genetic problem.
3. Myopia (Short sightedness)
The elongation of eyeball results in myopia. Such persons are not able to see distant objects clearly. The image of a distant object is formed in front of retina.
This problem can be rectified by using concave lens.
4. Hypermetropia (Long sightedness).
It happens when eyeball shortens. Such persons are not able to see near objects clearly. The image is formed behind retina.
Cure Convex lens is used to rectify this problem.