It's not clear what causes wet macular degeneration. The condition almost always develops in people who have had dry macular degeneration. But doctors can't predict who will develop wet macular degeneration, which is more severe and progresses more rapidly than dry macular degeneration.

Wet macular degeneration can develop in different ways:

  • Vision loss caused by abnormal blood vessel growth. Wet macular degeneration may develop when abnormal new blood vessels grow from the choroid — the layer of blood vessels between the retina and the outer, firm coat of the eye, called the sclera — under and into the macular portion of the retina. This condition is called choroidal neovascularization.

    These abnormal vessels may leak fluid or blood between the choroid and macula. The fluid 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.

  • Vision loss caused by fluid buildup in the back of the eye. Wet macular degeneration sometimes may develop when fluid leaks from the choroid and collects between the choroid and a thin cell layer, called the retinal pigment epithelium (RPE). This may cause retinal pigment epithelium detachment.

    The fluid beneath the RPE causes what looks like a blister or a bump under the macula.

Dec. 01, 2012