Question

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

• A. 1.5 cm
• B. 5 cm
• C. 2.5 cm
• D. 1.67 cm

Answer 1

The Correct Option is D

To solve the problem of finding the distance between the retina and the cornea-eye lens, we need to use the formula related to the power of a lens and its focal length in air, which is:

P = \frac{1}{f}

where \( P \) is the power of the lens in diopters (D) and \( f \) is the focal length in meters.

For a normal eye, the given information is:

• Power of the cornea \( P_1 = 40\, D \)
• Least converging power of the eye lens \( P_2 = 20\, D \)

The total power of the eye is the sum of the powers of the cornea and the lens:

P_{\text{total}} = P_1 + P_2 = 40 + 20 = 60\, D

Using the total power, we find the focal length of the eye:

f_{\text{total}} = \frac{1}{P_{\text{total}}} = \frac{1}{60}\; \text{m}

Converting meters to centimeters, we get:

f_{\text{total}} = \frac{1}{60} \times 100 \; \text{cm} = \frac{100}{60} \approx 1.67 \; \text{cm}

This calculated focal length represents the distance between the retina and the cornea-eye lens, which corresponds to the correct answer:

• 1.67 cm

Therefore, the distance between the retina and the cornea-eye lens is approximately 1.67 cm.