Explain the eye defect myopia. How can it be corrected with the help of a lens?

Myopia : This eye defect is also called short sightedness or near sightedness. It occurs when the image of a distant object is focused in front of the retina. This may be due to one of the following
(a) Lengthening of eyeball from the front of the back, (b) Due to increased convexity of the lens.
It can be corrected by using appropriate biconcave lenses.