Opacity of the lens in the eye leads to .

Select the correct alternative from those given below each statement and write the completed statement :
The part of eye that regulates and controls the amount of light entering the eye is ________

Elaborate the term Astigmatism. How this defect is corrected?

A short sighted person uses a spectacle of power $-0.4 \mathrm{D}$ to see very distant objects. How far can he see without using spectacle?