Eye Defect

The eyes are the most important sense organs of our body which provide visual perception. Because of this visual perception we are able to know what is happening around us in our external environment and accordingly we are able to act towards a particular situation. But sometimes these eyes may become defective due to various reasons.

In this post, we will discuss the various common defects of the eyes, the problems they pose to humans in their vision, the cause of these defects and the possible ways to overcome them.

1. MYOPIA

This defect is also known as shortsightedness. A person with this defect cannot see objects which are far off but can see objects which are nearby, this is a defect of vision in which far objects appear blurred but near objects are seen clearly. School going students are generally affected by this defect.

The image is focused in front of the retina rather than on it usually because the eyeball is too long or the refractive power of the eye’s lens too strong. Myopia can be corrected by wearing glasses/contacts with concave lenses these help to focus the image on the retina.

Myopia

Causes of Myopia:

One of the reason for this defect is the eye ball may get lengthened from front to back, in this defect the light rays from the object get focused in front of the retina. In order view the image of the object, the light rays from the object have to get converged on to the retina. Another possible reason for this defect is the lens may become too curved or convex which do not allow light rays to converge on the retina.

Correction of Myopia:

The defect can be rectified by using concave lens with correct power. The power of the spectacles used for this defect is denoted with a negative sign.

2. HYPERMETROPIA

Hyperopia (farsightedness) is a defect of vision in which there is difficulty with near vision but far objects can be seen easily. The image is focused behind the retina rather than upon it. This occurs when the eyeball is too short or the refractive power of the lens is too weak. Hyperopia can be corrected by wearing glasses/contacts that contain convex lenses.

Hypermetropia

Causes of Hypermetropia

One of the possible reason for this defect is the eye ball may become shortened from front to back which makes the light rays to travel beyond retina and meet behind the retina.  The light rays from the object without converging travel beyond retina and get focused behind the retina. So the image is not formed on the retina which is essential for viewing the object. The other reason for this defect is the lens may become too flat which do not allow the light the rays to converge to form an image on retina.

Correction of Hypermetropia

Persons with this defect have to wear spectacles with convex lenses with correct power. The power of the lens used for this defect will be shown with a positive sign.

3. PRESBYOPIA

It is an old age defect and commonly found in people above 40 years. A person with this defect cannot see objects which are nearby but can see objects clearly which are far off. The cause for this defect is the lens loses its elasticity as well as the culinary muscles also lose the ability to alter the shape of the lens. The defect can be rectified by using a convex lens as in the case of myopia defect.

Presbyopia

4. ASTIGMATISM

A person with this defect will get a blurred vision of the object. The reason for this defect is a part of the object is in focus while the other part is out of focus. The cause for this defect is the uneven curvature of cornea layer. This defect is generally rectified by using cylindrical lenses.

This defect is when the light rays do not all come to a single focal point on the retina, instead some focus on the retina and some focus in front of or behind it. This is usually caused by a non-uniform curvature of the cornea. A typical symptom of astigmatism is if you are looking at a pattern of lines placed at various angles and the lines running in one direction appear sharp whilst those in other directions appear blurred. Astigmatism can usually be corrected by using a special spherical cylindrical lens; this is placed in the out-of-focus axis.

Astigmatism

 

 

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