Question

Name the eye defect in which eye lens becomes cloudy or milky. Mention the method for its correction. A person uses a lens of power -1.0 D for correcting his distant vision and for correcting his near vision he uses a lens of power + 2.0 D. Calculate the focal length of the lenses required to correct these defects. Explain why a normal eye is not able to see clearly the objects placed closer than the near points.

Answer 1

The defect is call cataract, and it is corrected by surgery.
$P_1=-1.0D$
$\therefore p_1=\frac{1}{f_1}{f}_1=\frac{1}{p_1}=\frac{1}{-1.0}=-1m$
$\therefore p_2=+2.0D$
$f_2=\frac{1}{P_2}=\frac{1}{2}=0.5m$