Age Related Macular Degeneration


The macula lutea (or just "macula") is an area of the retina about five millimeters in diameter. It is centered on the optical axis of the eye, so that light falls on the macula from something small you look at directly. At the center at the macula is the fovea centralis (or just "fovea"). The fovea is about one millimeter in diameter and contains a very high concentration of cones. Indeed, about one-half of the axons in the optic nerve carry visual information from the fovea. Thus, most sharp visual accuity and almost all of color vision comes from the fovea. Areas outside the macula provide much less accuity, and since the photoreceptors are almost all rods, only provide black and white vision.

Thus, if there is degeneration of the macula, the sharp visual accuity is lost in the center of the field of vision, and the lower visual accuity of the peripheral vision is retained. Reading, for example, becomes difficult, while the patient can usually navigate around larger objects.

Types of Macular Degeneration

There are two main types of macular degeneration.



A diagnostic tool for assessing macular degeneration is optical coherence tomography. This provides an image showing the layers of the retina and choroid in a slice through the eye. This is determined by shining near infrared light into the eye. The light reflected from successive layers is then measured, providing a image of the layers. I will show a picture of this is class.

Angiograms provide an image of retinal blood vessels. These images are made following the injection of a fluorescent dye into the circulatory system.

Risk factors

Old age is the biggest risk factor. The prevalence increases in the 70s and in the 80s is found about a third of the population. Other risk factors include smoking, family history, white race, obesity, female gender.

Treatments

For both the dry and wet forms that are classified as intermediate, a special mixture of supplements called the AREDS 2 formulation is currently recommended by the National Eye Institute of NIH. Apparently, it often slows the progression from intermediate to advanced. But this formulation is only recommended for those with intermediate or with one eye with advanced, and not for anyone else. Normal diet and supplements would not provide this mix. (AREDS 2 formulation per day consists of 500 milligrams of vitamin C, 400 Units of vitamin E, 10 mg lutein, 2 mg zeaxanthin , 80 milligrams of zinc as zinc oxide,2 milligrams of copper as cupric oxide.)

There are drug treatments for the wet form, which are injected directly into the eyeball. These substances bind to and inactivate vascular endothelial growth factor (VEGF). For example, ranibizumab (Lucentis) is an antibody that does this.

A completely different technique involves injecting a substance into the circulation that binds to new blood vessels. This substance is then activated by a laser light striking it, which leads to destruction of the new blood vessels. This is called photodynamic therapy.

Patient G says he needs a +5 for reading. What are the units and is this a concave or convex lens?

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Which type of photoreceptor is concentrated in the fovea?

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What specific layer of cells, by functioning abnormally, appears most responsible for age related macular degeneration?

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