A nearsighted person cannot see objects clearly beyond 70 cm (the far point).If the patient has no astigmatism and contact lenses are prescribed,what is the power of the lens required to correct the patient's vision?
A)−0.7 diopters
B)−1.4 diopters
C)−2.9 diopters
D)−7.0 diopters
E)-700 diopters

Question

A nearsighted person cannot see objects clearly beyond 70 cm (the far point).If the patient has no astigmatism and contact lenses are prescribed,what is the power of the lens required to correct the patient's vision?
A)−0.7 diopters
B)−1.4 diopters
C)−2.9 diopters
D)−7.0 diopters
E)​-700 diopters

Quizplus · Accepted Answer

The power $P$ of a lens in diopters (D) is given by the formula $P = \frac{1}{f}$, where $f$ is the focal length in meters. For a nearsighted person who cannot see objects clearly beyond 70 cm (0.7 meters), the lens needs to have a focal length that brings parallel rays of light to focus at this far point. Thus, $P = \frac{1}{0.7} = -1.43$ D, approximately, because the lens must diverge the light rays. The negative sign indicates a diverging lens, which is required for correcting nearsightedness. The closest option is −1.4 diopters.

A Nearsighted Person Cannot See Objects Clearly Beyond 70 Cm