The person is suffering from myopia or short sightedness.
Myopia or short-sightedness. In normal eye, the far point is at infinity. The rays coming from distant object (at infinity) gets focussed on retina. In turn, the retina conveys the massage to brain via optical nerve.
Causes of Defect in Defective Eye. The defect arise due to either :
(i) the length of eye ball is elongated (becomes longer than normal)
(ii) the focal length of eye lens has decreased.
Due to either or both the causes, the eye is not able to focus the rays from distant object are retinal . Focussing is there at a point O in front of retina . Image formed on retina is , blurred.
The defective eye is however able to focus the object upto its far point .
Correction of Defect
We have observed that the defective eye has not been able to focus less inclined rays but has been able to focus more inclined rays.
To correct this defect, a concave or a divergent lens of appropriate focal length is placed in front of the eye so that parallel rays coming from infinity appear, after refraction through the lens , to come from the far point when eye is unaccommodated. These parallel rays from a distant object shall be brought to focus upon the retina. Obviously, the focal length of such a lens is equal to the distance of the far point from the eye .
