Visual Optics Practice Test

To determine the demand on accommodation for a 4 diopter myope reading at a distance of 20 cm, we first need to consider the optical characteristics of myopia and the relationship between distance, refractive error, and the required accommodation.

A 4 D myope means that the individual requires a corrective lens of +4 D to see distant objects clearly. The formula linking diopters (D) to the focal length (in meters) is given by \( f = \frac{1}{D} \). Therefore, for a 4 D myope, the person can see clearly at a distance of 0.25 meters (or 25 cm).

When this myope attempts to read at a distance of 20 cm, we need to understand how this falls in relation to their clear vision range. Since the myope can clearly see objects only as close as 25 cm without correction, reading at 20 cm is closer than their clear vision range. To read at this distance, they require additional accommodation beyond their natural power.

The demand on accommodation is calculated as the difference between the required power to focus clearly at the reading distance (20 cm) and their natural focusing ability. The power needed to focus at 20 cm (