What power contact lens must be used to correct the vision of a nearsighted person whose far point is 40 cm?
A) 2.5 diopters
B) -2.5 diopters
C) -3.6 diopters
D) -4.0 diopters
E) 4.0 diopters

Question

Quizplus · Accepted Answer

The power of a lens required to correct nearsightedness is negative. The formula for calculating the power of a lens is P = 1/f where P is the power in diopters and f is the focal length in meters. The far point of a nearsighted person is the distance beyond which they cannot see clearly. For a nearsighted person with a far point of 40 cm, their focal length is -40 cm or -0.4 m. Therefore, P = 1/(-0.4) = -2.5 diopters. Thus, the correct power contact lens for this person would be -2.5 diopters.

What Power Contact Lens Must Be Used to Correct the Vision