MedGen

Nearsightedness, also known as myopia, is an eye condition that causes blurry distance vision. People who are nearsighted have more trouble seeing things that are far away (such as when driving) than things that are close up (such as when reading or using a computer). If it is not treated with corrective lenses or surgery, nearsightedness can lead to squinting, eyestrain, headaches, and significant visual impairment.

Nearsightedness usually begins in childhood or adolescence. It tends to worsen with age until adulthood, when it may stop getting worse (stabilize). In some people, nearsightedness improves in later adulthood.

For normal vision, light passes through the clear cornea at the front of the eye and is focused by the lens onto the surface of the retina, which is the lining of the back of the eye that contains light-sensing cells. People who are nearsighted typically have eyeballs that are too long from front to back. As a result, light entering the eye is focused too far forward, in front of the retina instead of on its surface. It is this change that causes distant objects to appear blurry. The longer the eyeball is, the farther forward light rays will be focused and the more severely nearsighted a person will be.

Nearsightedness is measured by how powerful a lens must be to correct it. The standard unit of lens power is called a diopter. Negative (minus) powered lenses are used to correct nearsightedness. The more severe a person's nearsightedness, the larger the number of diopters required for correction. In an individual with nearsightedness, one eye may be more nearsighted than the other.

Eye doctors often refer to nearsightedness less than -5 or -6 diopters as "common myopia." Nearsightedness of -6 diopters or more is commonly called "high myopia." This distinction is important because high myopia increases a person's risk of developing other eye problems that can lead to permanent vision loss or blindness. These problems include tearing and detachment of the retina, clouding of the lens (cataract), and an eye disease called glaucoma that is usually related to increased pressure within the eye. The risk of these other eye problems increases with the severity of the nearsightedness. The term "pathological myopia" is used to describe cases in which high myopia leads to tissue damage within the eye. [from MedlinePlus Genetics]

Myopia, or nearsightedness, is a refractive error of the eye. Light rays from a distant object are focused in front of the retina and those from a near object are focused in the retina; therefore distant objects are blurry and near objects are clear (summary by Kaiser et al., 2004). For a discussion of genetic heterogeneity of myopia, see 160700. [from OMIM]

Any abnormality of the eye, including location, spacing, and intraocular abnormalities. [from HPO]

Inherited progressive cone degeneration. [from HPO]

Retinal phenotype characterized by cone photoreceptor dysfunction and preserved rod system. The abnormality is typically stationary or very slowly progressive and findings may include reduced central vision, color vision abnormalities, nystagmus and photophobia. [from HPO]

X-linked form of disease. [from MONDO]

A nonspecific term denoting degeneration of the retinal pigment epithelium and/or retinal photoreceptor cells. [from HPO]

A visual defect characterized by the inability to see as clearly in bright light as in dim light. The word hemeralopia literally means day blindness. [from HPO]

Transmission of gene defects or chromosomal aberrations/abnormalities which are expressed in extreme variation in the structure or function of the eye. These may be evident at birth, but may be manifested later with progression of the disorder. [from MeSH]

Retinitis pigmentosa (RP) refers to a heterogeneous group of inherited ocular diseases that result in a progressive retinal degeneration affecting 1 in 3,000 to 5,000 people (Veltel et al., 2008). Symptoms include night blindness, the development of tunnel vision, and slowly progressive decreased central vision starting at approximately 20 years of age. Upon examination, patients have decreased visual acuity, constricted visual fields, dyschromatopsia (tritanopic; see 190900), and the classic fundus appearance with dark pigmentary clumps in the midperiphery and perivenous areas ('bone spicules'), attenuated retinal vessels, cystoid macular edema, fine pigmented vitreous cells, and waxy optic disc pallor. RP is associated with posterior subcapsular cataracts in 39 to 72% of patients, high myopia, astigmatism, keratoconus, and mild hearing loss in 30% of patients (excluding patients with Usher syndrome; see 276900). Fifty percent of female carriers of X-linked RP have a golden reflex in the posterior pole (summary by Kaiser et al., 2004). Juvenile Retinitis Pigmentosa Autosomal recessive childhood-onset severe retinal dystrophy is a heterogeneous group of disorders affecting rod and cone photoreceptors simultaneously. The most severe cases are termed Leber congenital amaurosis (see 204000), whereas the less aggressive forms are usually considered juvenile retinitis pigmentosa (Gu et al., 1997). Autosomal recessive forms of juvenile retinitis pigmentosa can be caused by mutation in the SPATA7 (609868), LRAT (604863), and TULP1 (602280) genes (see LCA3, 604232, LCA14, 613341, and LCA15, 613843, respectively). An autosomal dominant form of juvenile retinitis pigmentosa (see 604393) is caused by mutation in the AIPL1 gene (604392). [from OMIM]

A defect in the focusing of light on the retina as in astigmatism, myopia, or hyperopia. [from NCI]

Any impairment to the vision. [from NCI]

An anomaly in the ability to discriminate between or recognize colors. [from HPO]

Achromatopsia is a condition characterized by a partial or total absence of color vision. People with complete achromatopsia cannot perceive any colors; they see only black, white, and shades of gray. Incomplete achromatopsia is a milder form of the condition that allows some color discrimination.

Achromatopsia also involves other problems with vision, including an increased sensitivity to light and glare (photophobia), involuntary back-and-forth eye movements (nystagmus), and significantly reduced sharpness of vision (low visual acuity). Affected individuals can also have farsightedness (hyperopia) or, less commonly, nearsightedness (myopia). These vision problems develop in the first few months of life.

Achromatopsia is different from the more common forms of color vision deficiency (also called color blindness), in which people can perceive color but have difficulty distinguishing between certain colors, such as red and green. [from MedlinePlus Genetics]

X-linked cone-rod dystrophy is a rare, progressive visual disorder primarily affecting cone photoreceptors (Demirci et al., 2002). Affected individuals, essentially all of whom are males, present with decreased visual acuity, myopia, photophobia, abnormal color vision, full peripheral visual fields, decreased photopic electroretinographic responses, and granularity of the macular retinal pigment epithelium. The degree of rod photoreceptor involvement is variable, with increasing degeneration. Although penetrance appears to be nearly 100%, there is variable expressivity with respect to age at onset, severity of symptoms, and findings (Hong et al., 1994). Genetic Heterogeneity of X-linked Cone-Rod Dystrophy Additional forms of X-linked cone-rod dystrophy include CORDX2 (300085), mapped to chromosome Xq27, and CORDX3 (300476), caused by mutation in the CACNA1F gene (300110) on chromosome Xp11.23. For a discussion of autosomal forms of cone-rod dystrophy, see CORD2 (120970). [from OMIM]

Non-heritable difficulty in distinguishing colors. [from NCI]

Normal color vision in humans is trichromatic, being based on 3 classes of cone that are maximally sensitive to light at approximately 420 nm (blue cones; 613522), 530 nm (green cones; 300821), and 560 nm (red cones; 300822). Comparison by neural circuits of light absorption by the 3 classes of cone photoreceptors allows perception of red, yellow, green, and blue colors individually or in various combinations. Dichromatic color vision is severely defective color vision based on the use of only 2 types of photoreceptors, blue plus green (protanopia) or blue plus red (deuteranopia; see 303800). Anomalous trichromacy is trichromatic color vision based on a blue, green, and an anomalous red-like photoreceptor (protanomaly), or a blue, red, and an anomalous green-like photoreceptor (deuteranomaly). The color vision defect is generally mild but may in certain cases be severe. Common variation in red-green color vision exists among both normal and color-deficient individuals (review by Deeb, 2005). [from OMIM]

An abnormality of the combined rod-and-cone response on electroretinogram. [from HPO]