Far point of the eye lens = v
v = -10 m
Object distance = u
u = ∞
Lens Formula:
\(\frac{1}{f}\,=\,\frac1v\,=\,\frac1u\)
\(\frac1f\,=\,\frac1{-10}\,-\,\frac1{∞}\)
Power of lens, P = 1/f
= -10 D
Hence the power of the lens required to correct the defect is -10 D. The lens used is a concave lens.