The individual is suffering from myopia. In this defect, the image is formed in front of the retina. Therefore, a concave lens is used to correct this defect of vision.

Object distance (u) = infinity = ∞

Image distance (v) = - 80 cm

Focal length = f

According to the lens formula,

\( \frac{1}{v}-\frac{1}{u}=\frac{1}{f}\)

\( -\frac{1}{80}-\frac{1}{∞}=\frac{1}{f}\)

\( \frac{1}{f}=-\frac{1}{80}\)

\( f=-80\,cm=-0.8\,m\)

We know,

\( Power,P=\frac{1}{f(in \,meters)}\)

\( P=\frac{1}{-0.8}=-1.25\,D\)

A concave lens of power - 1.25 D is required by the individual to correct his defect.

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