Macular Degeneration

Macular degeneration is a general term used to describe dysfunction of the central portion of the retina, called the macula, inside our eyes. The macula gives us our ability to discriminate fine visual detail. Without any macular function, a person can be considered legally blind. Most cases of macular degeneration never reach this extreme but can be a nuisance and a handicap, nonetheless. Macular degeneration does not lead to complete blindness where there is no light perception whatsoever.

To understand macular degeneration, it is important to understand some ocular anatomy. The retina is specialized nervous tissue that lines the inside of the back of our eyes and allows us to sense light.  These sensations, which are only minimally processed by the retina, are sent via the optic nerve to the occipital cortex in the brain where they are processed to allow visual perception. There are different layers of cells in the retina, which must all work together to integrate the sensory input that is sent to the brain, but it is the photoreceptor cells, called rods and cones, which allow us to sense light entering our eyes. Rods are more sensitive to light and allow us to see in very low light but not to appreciate color or much detail. Cones allow us to see color and to discriminate fine detail.  The distribution of these photoreceptors varies throughout the retina. In the macula, the concentration of cones is the highest, and in the center of the macula (called the fovea), only cone cells are found (see Figures above). The cone density in the retina decreases, and the rod concentration increases, as you go farther away from the macula, so that the peripheral retina is almost all rod receptors. It is predominantly the loss of functioning cone receptors in the macula, which causes us to lose vision when we have macular degeneration.

There are different types of macular degeneration that can present at different ages. Some are inherited or occur as a genetic mutation. Other types can occur as a result of systemic and ocular disease, such as infections (septicemia, choroiditis), chronic inflammation (uveitis), autoimmune diseases (systemic lupus erythematosus), ocular trauma, or retinal detachment.  The most common type of macular degeneration in the United States is associated with advancing age. The specific cause for age-related macular degeneration (AMD) is still uncertain, so it is attributed to the general aging of the rods and cones and their surrounding tissues.

Age-related macular degeneration (AMD) clearly has a hereditary component associated with its development, which has been ascertained through observation of families over time.  You can now be tested for AMD-associated genes, but this knowledge is not useful since it does not change treatment in any way (and may contribute to your general anxiety). Environment also plays a role in the development of AMD, and proactive treatments therefore revolve around environmental modifications, changes in lifestyle, or nutritional supplements.

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