If I cannot focus on anything closer than 40 cm from my eyes,what type of correction lens would I need to buy to be able to read at the normal near point of 25 cm?
A)-1.5 diopters
B)-0.5 diopters
C)0 diopters
D)0.5 diopters
E)1.5 diopters

Question

Quizplus · Accepted Answer

The reduction in the near point of 40 cm to the normal near point of 25 cm indicates presbyopia, which is the age-related loss of accommodation. Accommodation is the ability of the eye to change its focus from distant to near objects. The correction required for presbyopia is a converging lens, which is also known as a plus lens. The corrective power of the lens required to restore the near point of 25 cm can be calculated as follows:

1/f = 1/di + 1/do, where f is the focal length of the lens, di is the distance of the object from the lens (i.e., the near point), and do is the distance of the object from the eye (i.e., the far point).

In this case, di = 25 cm and do = infinity (i.e., the eye is assumed to have no refractive error). Substituting these values in the equation above, we get:

1/f = 1/25 + 1/infinity = 0.04

Therefore, f = 25 cm/0.04 = 625 cm.

The corrective power of the lens required is the reciprocal of the focal length in meters, expressed in diopters. Therefore, the lens required is a +1.5 diopter lens (rounded to the nearest half diopter), which is available in the market as a reading or progressive addition lens.

If I Cannot Focus on Anything Closer Than 40 Cm