Nearsightedness is when the eyes focus incorrectly, making distant objects appear blurred.

A nearsighted person sees near objects clearly, while objects in the distance are blurred. As a result, someone with myopia tends to squint when viewing far away objects. This characteristic is the basis of the word "myopia," which comes from two Greek words: myein, meaning shut, and ops, meaning eye.

A nearsighted person can easily read the Jaeger eye chart (the chart for near reading), but finds the Snellen eye chart (the chart for distance) difficult to read. This blurred vision results when the visual image is focused in front of the retina, rather than directly on it.

Nearsightedness occurs when the physical length of the eye is greater than the optical length. For this reason, it often develops in the rapidly growing school-aged child or teenager, and progresses during the growth years, requiring frequent changes in glasses or contact lenses. It usually stops progressing as a person finishes growing in his or her early twenties.

Nearsightedness affects males and females equally. Those with a family history of nearsightedness are more likely to develop it. Most eyes with nearsightedness are entirely healthy, but a small number of people with myopia develop a form of retinal degeneration.