Defects of Vision and Care of the Eyes.

 •Defects of Vision

We now know that a normal eve can see obiects over a wide range of distances varying from (nearly) 25 cm to infinity.

 Sometimes inspite of all precautions and proactive actions, our eyes may develop some defects. These can be due to a variety of reasons. In such a case the eye may not be able to see objects clearly over its normal wide range of distances. The eye may have one, or both of the following two (common) optical defects:

 1. Myopia (or near sightedness) 

2. Hypermetropia (or far sightedness)

 Let us talk about these defects in some detail.

1) Myopia (or near sightedness): Myopia is a defect of the eye due to which the eye is not able to see distant objects clearly. In such an eye, the light rays from a distant object, arriving at the eye lens, get converged at a point in front of the retina. This defect may arise due to either (i) excessive curvature of the cornea, or (ii) elongation of the eyeball.

  This defect can be corrected by using a concave (diverging) lens of appropriate focal length.

2). Hypermetropia (or far sightedness): We may have seen some middle aged people holding a book somewhat away from their eyes to read it properly. This is because they are suffering from hypermetropia. In this case the image of a nearby object gets formed behind the retina. This defect arises due to either (1) the focal length of eye lens becoming too large or (2) the eyeball getting shortened.

This defect can be corrected using a convex (converging) lens of appropriate focal length.

 Sometimes during old age, the eye lens of some people, becomes hazy or even opaque. This happens because of the development of a membrane over it. When this happens, the person is said to have cataract. This leads to decrease, or loss, of vision of the eye. It is possible to restore vision in such cases. This is done by replacement of the opaque lens with a new artificial lens.

• Care of the Eyes

It is our eyes that allow us to see and interpret the shapes, colours and dimensions of different objects in the world. Our eyes are, therefore, a great asset to all of us. We, therefore, need to take proper care to protect them and keep them healthy.

The following precautions have been suggested to ensure the health,care and proper functioning of the human Eye.

1)Have a regular check-up. If so advised, use the correct spectacles.

 2)Never look at the sun, or any other powerful light source, directly. 

3)Have sufficient light in the room when you are reading, writing or watching television. Poor lightning in the room causes eye strain. 

4)Try not to spend too much time looking continuously at the computer screen, or television. It can cause eye strain. 

5)Eat a balanced diet having lots of fruits and vegetables. Lack of vitamin A, in the food, is responsible for many eye problems including night blindness.

6) Gently wash eyes frequently with clean (potable) water. 

5)Know your family history. Some of the vision problems may be inherited, i.e. they may run in the family.