Question

For a normal eye, the cornea of the eye provides a converging power of $40\text{D}$, and the least converging power of the eye lens behind the cornea is $20\text{D}$. Using this information, the distance between the retina and the cornea-eye lens can be estimated to be -

• A. $1.5\text{cm}$
• B. $5\text{cm}$
• C. $2.5\text{cm}$
• D. $1.67\text{cm}$

Answer 1

The correct option is D $1.67\text{cm}$

For a normal eye, rays coming from infinity should converge on the retina without effort. When we look at an object at infinity, the lens offers minimum power and hence the combination gives effective power, given by,

$P_{eff}=40\text{D}+20\text{D}=60\text{D}$

Distance between the retina and the cornea eye = focal length of the eye-lens

$f=\frac{1}{P_{eff}}=\frac{1}{60}\text{m}\approx 1.67\text{cm}$

<!--td {border: 1px solid #ccc;}br {mso-data-placement:same-cell;}--> Hence, $\left(D\right)$ is the correct answer.