Myopia is a refractive defect of the eye in which light focuses in front of the retina. Those with myopia are often described as nearsighted or short-sighted in that they typically can see nearby objects clearly but distant objects appear blurred. The opposite of myopia is hyperopia or "farsightedness".

Myopia is the most common eyesight problem in the world. About one quarter of the adult population in the United States has myopia. In places like Japan, Singapore and Taiwan, as many as one in three or one in two of the adult population is myopic. It is thought that this is due to the focus on academics in these countries.

Mainstream ophthalmologists and optometrists most commonly correct myopia through the use of corrective lenses, such as glasses or contact lenses. It may also be corrected by refractive surgery, such as LASIK. The corrective lenses have a negative dioptric value (i.e. are concave) which compensates for the excessive positive diopters of the myopic eye.