How do you correct the eye defect Myopia?

Myopia or near-sightedness or short-sightedness is one such defect in which a person is unable to see far away things clearly. In this defect, a person can see objects placed at certain distance (far point) from the eye only but everything beyond that distance appears blurry. The maximum distance upto which a person can see things clearly that is image is formed on retina is called the far point. Some of the causes of myopia are:

● Increase in the axial length of the eye, which eventually shifts the retina to a certain level.

● Cornea/lens becomes too curved for the length of the eyeball.

● If parents are myopic, there are high chances that child too can have this defect.

Actually what happens in myopia is, the rays coming from the object, after refraction from the lens, converges to a point before the retina as retina is the screen where the image should be obtained. In other words, the focal length of the eye lens decreases. So the rays are focused before retina and the image is not obtained clearly leading to blurry image.

Now the main objective is to focus the light on the retina. So a double-concave lens is used in front of the eye to fulfill this purpose. A double concave lens spread the light coming from the far away placed object that is makes the light rays parallel so that the rays converge at retina and thus forming a clear image. In other words, the concave lens brings the image of the object, placed beyond the far point, in between the far point & the least distance of distinct vision. Now this image acts an object for convex lens and image is formed on retina. The focal length, f of the lens should be equal to the negative of distance of far point,D.

f = -D