Contributor: Gordon K. Klintworth
Myopia (nearsightedness) is an ocular abnormality in which light from a visualized object focuses in front of the retina. It is the most common visual disorder in the world. It accounts for ~25% of the adult population in the United States. In Asia it is even more common in the Chinese and Indians. Two main types of myopia are recognized: refractive myopia [myopia - refractive] and lenticular myopia [myopia - lenticular]. Three types of refractive myopia are recognized: stationary myopia [myopia - stationary], progressive myopia [myopia - progressive] and late myopia [myopia - late]. Depending on its severity myopia is divided into high myopia [myopia - high] and low myopia [myopia - low]. Genetic and ocular developmental factors play a role in the pathogenesis of myopia. Myopia is often associated with prematurity. Affected individuals often have a low birth weight and eyelid closure may be present in infants. Genes for myopia have been mapped to 11 loci (MYP1 [myopia-1], MYP2 [myopia-2], MYP3 [myopia-3], MYP4 [myopia-4], MYP5 [myopia-5], MYP6 [myopia-6]), MYP7 [myopia-7], MYP8 [myopia-8], MYP9 [myopia-9], MYP10 [myopia-10], and MYP11 [myopia-11]. PAX6 may also play a role in the development of myopia. Myopia is associated with several ocular conditions (ocular albinism type II [albinism - ocular type II], pigmentary retinopathy, retinopathy of prematurity) and systemic disorders of fibrillin (Marfan syndrome), collagen (Stickler syndrome, Knobloch syndrome), perlecan (Schwartz-Jampel syndrome type 1), as well as Ehlers-Danlos syndrome type VI, sinus node disease and myopia, and Down syndrome. In animals an eye elongates markedly if the eyelids are kept closed before the eye has fully grown, especially if this has been done from birth. Myopia can be corrected with glasses or contact lenses. Refractive surgical procedures such as LASIK and LASEK are used to treat myopia in selected patients.