Macular degeneration is the leading cause of blindness in people over the age of 55, affecting more than 10 million Americans. The disease occurs when the central portion of the retina (the macula) deteriorates, resulting in impaired vision or blindness.
One definition of Age-Related Macular Degeneration (ARMD) is pigmentary changes in the macula or typical drusen (small bright structures seen in the retina and in the optic disc) associated with visual loss to the 20/30 level or worse, not caused by cataract or other eye disease in individuals over 50 years of age. Other definitions do not include age or visual acuity criteria. ARMD is the leading cause of irreversible severe visual loss in persons over 65 years of age.
There are two stages: Atrophic/nonexudative and Neovascular/exudative. Atrophic/nonexudative has drusen and/or pigmentary changes in the macula. Neovascular/exudative has growth of blood vessels underneath the retina.
Prevalence increases with age. Over 75 years; one quarter of men and one third of women will have evidence of ARMD.; The prevalence of severe visual loss from ARMD increases with age. 2.2% of patients over 65 years of age are blind in one or both eyes from ARMD. The atrophic/nonexudative stage accounts for 20% of cases of severe visual loss. The neovascular/exudative stage accounts for 80% of cases of severe visual loss.
The cause of macular degeneration is considered to be visible light which can result in the formation and accumulation of metabolic byproducts in the retinal pigment epithelium (RPE), which normally helps remove metabolic byproducts from the retina. The excess accumulation of these metabolic byproducts interferes with the normal metabolic activity of the RPE and can lead to the formation of drusen.
Some postulate these changes are initiated by isolated regions of choriocapillaris vascular failure. These proceedings cause the RPE to degenerate, resulting in photoreceptor loss. As the photoreceptors disintegrate, the inner nuclear layer collapses and contacts BruchÕs membrane, initializing the degeneration of the outer retinal layers.
Some theorize that the mechanism of damage may be through ultraviolet radiation-induced oxidation and free radical formation within these structures.
Risk factors include: Excess sunlight exposure; Blue or light iris color; Hyperopia; History of cardiovascular disease (hypertension, circulatory problems); Short height; History of lung infection; and Cigarette smoking.
Macular degeneration is diagnosed by opthalmoscopy, which shows drusen (small bright structures seen in the retina and in the optic disc), retinal pigment epithelial atrophy or clumping in the macula.
Standard lab tests are recommended to identify risk factors, especially cardiovascular disease.
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