Final answer:
The dioptric demand for a working distance of 40 cm is found by taking the inverse of the distance in meters, resulting in a demand of 2.50 diopters.
Step-by-step explanation:
To find the dioptric demand for a particular working distance, you apply the simple formula P = 1/d, where P is the power in diopters and d is the distance in meters. In the case of a reading distance of 40 cm (which is 0.40 m), the dioptric demand would be 1/0.40 m, which equals 2.50 diopters (D). This means that for a person to see clearly at a distance of 40 cm, their lens must have a power of +2.50D.
A diopter is the unit of measurement used for an eye prescription. The focusing strength of your glasses or contacts is measured in diopters. In other words, diopters measure how powerful your prescription is. A higher prescription will have larger numbers, whereas a milder prescription will have smaller numbers
Presbyopia is a refractive error that makes it hard for middle-aged and older adults to see things up close. It happens because the lens (an inner part of the eye that helps the eye focus) stops focusing light correctly on the retina (a light-sensitive layer of tissue at the back of the eye).