Signs and symptoms edit
In humans, there are two principal types of albinism, oculocutaneous, affecting the eyes, skin and hair, and ocular affecting the eyes only.
Most people with oculocutaenous albinism appear white or very pale as the melanin pigments responsible for brown, black, and some yellow colorations are not present. Ocular albinism results in pale blue eyes, and may require genetic testing to diagnose.
Because individuals with albinism have skin that entirely lacks the dark pigment melanin, which helps protect the skin from the sun's ultraviolet radiation, their skin can burn more easily from overexposure.[1]
The human eye normally produces enough pigment to color the iris blue, green or brown and lend opacity to the eye. However, there are cases in which the eyes of an albinistic person appear red, pink or purple, depending on the amount of pigment present, due to the red of retina being visible through the iris. Lack of pigment in the eyes also results in problems with vision, both related and unrelated to photosensitivity.
Those afflicted with albinism are generally as healthy as the rest of the population (but see related disorders below), with growth and development occurring as normal, and albinism by itself does not cause mortality,[2] although the lack of pigment blocking ultraviolet radiation increases the risk of melanomas (skins cancers) and other problems.
Visual problems edit
Development of the optical system is highly dependent on the presence of melanin, and the reduction or absence of this pigment in sufferers of albinism may lead to:
- Misrouting of the retinogeniculate projections, resulting in abnormal decussation (crossing) of optic nerve fibres[1]
- Photophobia and decreased visual acuity due to light scattering within the eye (ocular straylight)[1][3]
- Reduced visual acuity due to foveal hypoplasia and possibly light-induced retinal damage[1]
Eye conditions common in albinism include:
- Nystagmus, irregular rapid movement of the eyes back and forth, or in circular motion.[1]
- Astigmatism, irregular shaped cornea requiring additional cylindrical corrective lenses in spectacles.[4]
- Amblyopia, decrease in acuity of one or both eyes due to poor transmission to the brain, often due to other conditions such as strabismus.[1]
- Optic nerve hypoplasia, underdevelopment of the optic nerve
Some of the visual problems associated with albinism arise from a poorly developed retinal pigment epithelium (RPE) due to the lack of melanin.[citation needed] This degenerate RPE causes foveal hypoplasia (a failure in the development of normal foveae), which results in eccentric fixation and lower visual acuity, and often a minor level of strabismus.
The iris is a sphincter formed from pigmented tissue that contracts when the eye is exposed to bright light, to protect the retina by limiting the amount of light passing through the pupil. In low light conditions the iris relaxes to allow more light to enter the eye. In albinistic subjects, the iris does not have enough pigment to block the light, thus the decrease in pupil diameter is only partially successful in reducing the amount of light entering the eye.[citation needed] Additionally, the improper development of the RPE, which in normal eyes absorbs most of the reflected sunlight, further increases glare due to light scattering within the eye.[5] The resulting sensitivity (photophobia) generally leads to discomfort in bright light, but this can be reduced by the use of sunglasses and/or brimmed hats.[6]
- ^ a b c d e f Chen, Harold (2006). Atlas of genetic diagnosis and counseling. Totowa, NJ: Humana Press. pp. 37–40. ISBN 1-58829-681-4. Retrieved 22 July 2010.
- ^ Cite error: The named reference
eMedicine1was invoked but never defined (see the help page). - ^ Kruijt B et al. "Ocular straylight in albinism". Optom Vis Sc 2011;88:E585-E592
- ^ Carden SM, Boissy RE, Schoettker PJ, Good WV (February 1998). "Albinism: modern molecular diagnosis". The British Journal of Ophthalmology. 82 (2): 189–95. doi:10.1136/bjo.82.2.189. PMC 1722467. PMID 9613388.
{{cite journal}}: CS1 maint: multiple names: authors list (link) - ^ "Albinism—Review of Optometry Online".
- ^ "Facts about Albinism", by Dr. Richard King et al.