Defects of vision and their correction (Eye)

 

The ability to see is called vision. It is also eyesight. Vision is known as 'drishti' in Hindu.  Sometimes the eye of a person cannot focus the image of an object on the retina properly. In such cases the vision of a person becomes blurred and he cannot see either the distant objects or nearby objects (or both) clearly and comfortably. The person is said to have a defects of vision. The defects of vision are also known as defects of eye. There are three common defects of vision (or defects of eye). These are:

1. Moypia (Short -sigtedness or Near- sightedness) 
2. Hypermetropia (Long - sightedness or Far -sightedness), and
3. Presbyopia

These are the refractive defects of vision because are caused by the incorrect reflection of light rays by the eye- lens. These defects of vision can be corrected by using suitable spherical lense (convex lenses or concave or spectricales. We will now describe all these defects of vision and their correction, one by one. Let us start with myopia.

1. Myopia (Short - sightedness or Near -sightedness)

A short - sighted means that the short sight of the person (to see nearby objects) is normal but long Sight (long see distant objects) is defective. Myopia (or short- sightedness) is that defects of vision due to which a person cannot see the distant object clearly (through he can see the nearby objects clearly). .

For example, a child having the defect called myopia (or short -sightedness) and sitting on the back benches in the class cannot read the writting on blackboard clearly through in the class cannot read the writting on blackboard clearly through he can read his book comfortably. (The far point of an eye suffering from myopia is less than infinity). Such va person an see clearly only up to a distance of few metres (or even less).

The  defect of eye called myopia (or short -sightedness) is caused:

• due to high converging power of eye -lens (because of its short focal length) or
• due to eye- ball being too long.

In some cases, in an eye suffering from myopia, the ciliary muscles attached to the eye- lens do not relax sufficiently to make the eye- lens thinner to reduce its converging power. So due to the greater converging power of the eye- lens in myopia thinner to a distance objects is front of the retina and hence the eye cannot see it clearly.  In other cases, in the eye suffering from myopia, the eye- ball is too long due to which the retina is at a larger distance from the eye- lens. 

The condition also result in the formation of the image of a distant objec in front of the retina (even through the eye - lens have correct converging power.