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Causes
By Mayo Clinic staff
Wet macular degeneration develops when abnormal new blood vessels grow from the choroid — the layer of blood vessels sandwiched between the retina and the outer, firm coat of the eye called the sclera — under and into the macular portion of the retina (a process known as choroidal neovascularization). These abnormal vessels leak fluid or blood, which is why this form of macular degeneration is called "wet." Fluid or blood between the choroid and macula interferes with the retina's function and causes your central vision to blur. In addition, what you see when you look straight ahead becomes wavy or crooked, and blank spots block out part of your field of vision.
Eyes with the wet form of macular degeneration almost always show signs of the dry form — yellow fat-like deposits (drusen) and mottled pigmentation of the retina.
The wet form accounts for about 15 percent of all cases, but it's responsible for most of the severe vision loss that people with macular degeneration experience. If you develop wet macular degeneration in one eye, your odds of getting it in the other eye increase greatly.
Much like the dry form of macular degeneration, the wet form may be caused by a breakdown in the eye's waste-removal system. The light-sensitive cells in the retina called cones and rods produce waste. If this waste accumulates, it interrupts the retina's nutrient supply, and retinal tissue deteriorates. Whether this is the mechanism that triggers the growth of abnormal blood vessels is unclear, and it remains the subject of scientific study.
With the wet form of macular degeneration, sight loss is usually severe and rapid, often deteriorating to 20/200 vision or worse, occurring within weeks or months. When vision is 20/200 or worse in both eyes, you're considered legally blind.
Retinal pigment epithelial detachment
Another form of wet macular degeneration, called retinal pigment epithelial detachment, occurs when fluid leaks from the choroid and collects between the choroid and the next-deeper cell layer, the retinal pigment epithelium (RPE). No abnormal choroidal blood vessel growth is apparent when the RPE is detached. Instead, fluid beneath the RPE causes what looks like a blister or a bump under the macula.
Although this kind of macular degeneration causes symptoms similar to those of typical wet macular degeneration, your vision can remain relatively stable for many months or even years before it deteriorates. Eventually, however, RPE detachment tends to evolve to the more common wet form of macular degeneration associated with the development of newly growing abnormal choroidal blood vessels.
