The defects of the human eye are as follows –
Myopia – It is also known as short-sightedness in which nearby objects appear to be seen clearly, and far objects appear to be seen blurred. It can be corrected by a concave lens.
Hypermetropia – It is also called farsightedness in which far away appear to be seen clearly and nearby objects appear to be blurred. It can be corrected using the convex lens.
Astigmatism – This defect causes impaired vision due to which some parts of the picture may appear clear, whereas some parts may appear blurred. It can be corrected with the help of spherical or cylindrical lenses.