Which defect of vision can be rectified by
a) by using a concave lens
b) by using a convex lens

(a). by using a concave lens

Myopia

This is a defect of vision in which far objects appear blurred but near objects are seen clearly. 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 with concave lenses these help to focus the image on the retina.

(b). by using convex lens

Hyperopia

This 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 that contain convex lenses