What power contact lens is needed to correct for farsightedness where the uncorrected near point is 75 cm?
A)+2.7 D
B)-2.7 D
C)+5.3 D
D)-5.3 D

Question

Quizplus · Accepted Answer

The power of the lens needed to correct farsightedness (hyperopia) can be calculated using the lens formula: Power (P) = 1/focal length (in meters). The uncorrected near point indicates the closest point at which the eye can focus on an object, which is 75 cm or 0.75 meters in this case. To correct this, the lens must bring this point to the normal near point of 25 cm or 0.25 meters. The lens power required is P = 1/0.25 - 1/0.75 = 4/0.25 - 4/0.75 = 4 - 1.33 = 2.67 diopters, which is approximately +2.7 D. A positive power indicates a converging lens, which is used to correct farsightedness.

What Power Contact Lens Is Needed to Correct for Farsightedness