Nearsightedness occurs when light entering the eye focuses in front of the retina instead of directly on it. This is caused by a cornea that is steeper, or an eye that is longer, than a normal eye. Nearsightedness causes difficulty seeing at a distance. It is often discovered in school-age children who report having trouble seeing the board. Nearsightedness usually becomes progressively worse through adolescence and stabilizes in early adulthood.

Nearsightedness is characterized by blurry distance vision or squinting. A simple vision test and refraction are used to detect the problem. Vision is generally corrected with glasses or contact lenses. Refractive procedures, such as LASIK, can be considered for adults once the prescription has remained stable for at least one year.