The far point of a myopic person is 80 cm in front of the eyes. What is the nature and power of the lens…
The far point of a myopic person is 80 cm in front of the eyes. What is the nature and power of the lens required to enable him to see very distant objects distinctly?
Solution
A **concave lens** is used for a myopic eye whose far point is at $x = 80\ \text{cm}$.
For viewing a far distant object the lens must form its image at the far point, so
$f = -x = -80\ \text{cm}$
$P = \dfrac{100}{f\ (\text{cm})} = \dfrac{100}{-80} = -1.25\ \text{D}$
So a concave lens of power $-1.25\ \text{D}$ is required.