Nearsightedness and Farsightedness

Not all of us have the so called normal eyes described by Figure (1). There is increasing evidence that those who do a lot of close work as children end up with a condition called nearsightedness or myopia where the eye is elongated and light from infinity focuses inside the eye as shown in Figure (2a). This can be corrected by placing a diverging lens in front of the eye to move the focus back to the retina as shown in Figure (2b).
The opposite problem, farsightedness, where light focuses behind the retina as shown in Figure (3a) is corrected by a converging lens as shown in Figure (3b).

Figure 1: Parallel light rays from a distant object are focuses on the retina when the ciliary muscles are in the resting position.

Figure 2: Nearsightedness can be corrected by a convex lens..

Figure 3: Farsightedness can be corrected by a convex lens

مواضيع ذات صلة

Mirror reflections

The sensation of color

Physiochemistry of color vision

The mechanism of color vision

The chromaticity diagram

Measuring the color sensation

Color depends on intensity

Aberration

The ω,k four-vector

Moving sources

Anomalous refraction

The intensity of reflected light