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 most 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.

• The dry form of macular degeneration is the most common. Early in the disorder, yellow deposits called drusen appear in the retina. The deposits are a combination of protein and lipid, and their appearance initially might not be associated with any symptoms. Apparently some drusen is normal with age. But as the disorder advances, photoreceptors, which are mainly cones, begin to atropy and the vision becomes fuzzy. The fundamental problem is the retinal pigment epitelium, which provides a crucial supportive role for the photoreceptors.



• The wet form of macular degeneration is usually more serious and affects about 10% of the patients. This type of macular degeneration typically develops from the dry form, although the dry does not necessary lead to the wet form and by itself can cause damage. Again, the retinal pigment epithelium is abnormal, but here it leads to abnormal growth of blood vessels occurs under the macula. Moreover, the new blood vessels are faulty with a tendency to be leaky. Fluid leaving the blood vessels and scaring can severely damage the macula and cause serious visual problems fairly quickly. This form tends cause straight lines to appear crooked as well as blur the vision.

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

There are now drug treatments for the wet form, which are injected directly into the eyeball. These substance bind to and inactivate vacular 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 light striking it, leading to destruction of the new blood vessels.