Definition of Macular Degeneration

Macular degeneration: An eye disease that progressively destroys the macula, the central portion of the retina, impairing central vision. Macular degeneration rarely causes total blindness because only the center of vision is affected. However, injury to the macula in the center of the retina can impair the ability to see straight ahead clearly and sometimes make it difficult to read, drive, or perform other daily activities that require fine central vision.

The macula is in the center of the retina at the back of the eye. As we read, light is focused onto the macula where millions of cells change the light into nerve signals that travel to the brain and tell it what we are seeing. This is our central vision. With normal central vision, we are able to read, drive, and perform other activities that require fine, sharp, straight-ahead vision.

There are a number of forms of macular degeneration that affect children and younger people, including congenital macular degeneration, central tapetal degeneration, Best's Disease, Stargardt's Disease and Juvenile Retinoschisis. However, the disease occurs most commonly in people over 60 years of age. Within this group, the disorder is termed age-related macular degeneration (AMD or ARMD).

There are two types of AMD -- the wet type and the far more frequent dry type. Neither type causes pain. An early symptom of wet AMD is that straight lines appear wavy. This happens because newly formed abnormal blood vessels leak fluid under the macula. The fluid raises the macula from its normal place at the back of the eye and distorts vision. Another sign that a person may have wet AMD is rapid loss of central vision. This is different from dry AMD in which loss of central vision occurs slowly. An advanced form of age-related dry macular degeneration (AMD) is geographic atrophy, which leads to progressive and irreversible loss of visual function. Geographic atrophy causes sharply demarcated atrophic lesions of the outer retina, resulting from loss of retinal pigment epithelium, photoreceptors, and choriocapillaris. Geographic atrophy is also known as atrophic age-related macular degeneration.

In both dry and wet AMD, the person may also notice a blind or blurred area near the center of the vision. If any of these changes in vision is noticed, an ophthalmologist should be consulted without delay.

Kasper, D.L., et al., eds. Harrison's Principles of Internal Medicine, 19th Ed. United States: McGraw-Hill Education, 2015.

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