Question

If the lens of a person’s eye is removed because of cataracts (as has been done since ancient times), why would you expect a spectacle lens of about 16 D to be prescribed?

a) To increase the focal length of the eye.

b) To decrease the focal length of the eye.

c) To provide magnification.

d) To correct hyperopia.

Answer 1

When the lens of a person's eye is removed due to cataracts, a spectacle lens of about 16 D is prescribed to decrease the focal length of the eye and improve vision.

Step-by-step explanation:

When the lens of a person's eye is removed due to cataracts, a spectacle lens of about 16 D is often prescribed to provide correction. The answer is b) To decrease the focal length of the eye.

By decreasing the focal length of the eye, the spectacle lens compensates for the loss of focusing power caused by the removed lens. This helps to bring objects into clearer focus and improve the person's vision.

For example, if someone's eye has a focal length of 50 cm without the lens, the prescription of a spectacle lens with a power of 16 D would allow them to achieve a focal length of 1/((1/50) + (1/16)) = 12.31 cm, which is closer to the typical focal length of a healthy eye (approximately 17 mm or 1.7 cm).