Question

Nupur need a lens of power -4.5 d for correction of her vision what kind of defect in vision is she suffering from

Answer 1

shortsightedness is a defect due to which a person can see objects at short distance easily bt cannot see distant objects .
this defect is corrected by placing a diverging lens i.e.concave lens
which have always negative focal length
and therefore power
as power =1/ focal length

Answer 2

Short-Sightedness

It is the quality of being short-sighted; inability to see things clearly unless they are relatively close to the eyes.
this can be  corrected by  a diverging lens .

Diverging lens

When parallel rays of light pass through a concave lens the refracted rays diverge so that they appear to come from one point called the principal focus.
which have always negative focal length
and so the power is 
                  Power =1/ Focal length