About Wet Age-Related Macular Degeneration
Macular degeneration is a serious condition that can rapidly lead to blindness
The retina is a highly structured component of the human eye. Figure 1 depicts the anatomy of the human eye, as well as magnified sections of healthy and diseased retinas. In the healthy retina, the photoreceptors (PR) are closely affiliated with a single layer of cells termed the retinal pigment epithelial (RPE) cells. The RPE cells overlie Bruch's membrane and a dense bed of blood vessels called the choroid.
Figure 1. Anatomy of the human eye. A) Schematic diagram of the human eye. The major components of the eye are labeled. The retina lines the back of the eye and is nourished by the choroid, a dense bed of blood vessels. B) Schematic diagrams of a portion of the retina. The location of the photoreceptors (PR), retinal pigment epithelial cells (RPE), Bruch's membrane, and the choroid are displayed. In a healthy retina, the blood vessels of the choroid supply nutrients and oxygen to the retina and remove waste products. In dry age-related macular degeneration, the efficient removal of waste products is diminished resulting in the accumulation of debris or drusen, depicted as yellow matter, under the RPE layer. In wet age-related macular degeneration, new, defective blood vessels grow from the choroid into the retina. These vessels leak and bleed and damage the retina rapidly leading to blindness. The graph displays the course of dry and wet age-related macular degeneration. While dry age-related macular degeneration results in a gradual loss of visual acuity over time, progression to wet age-related macular degeneration results in the rapid loss of vision.
The function of the RPE cells is to nurture the photoreceptors. Each day, the tips of the photoreceptors are damaged by the absorption of light and are shed. The RPE have the important responsibility of engulfing and eliminating the damaged tips. The RPE also recycle vitamin A metabolites, which are required for sight. The choroid supplies nutrients and oxygen to the retina and removes waste products.
Dry (or nonexudative) age-related macular degeneration is the disease that occurs with age as these normal retinal functions begin to break down. Initially, deposits of debris, termed drusen, accumulate under the RPE layer, and then the RPE cells and photoreceptors gradually degenerate. Patients experience a slow loss of visual acuity. Dry age-related macular degeneration is very common, affecting 25% of people over the age of 65. While dry age-related macular degeneration may diminish the quality of life for those affected, it does not rapidly lead to blindness.
Wet (or exudative) age-related macular degeneration develops in 10% of patients with dry age-related macular degeneration. In these patients, new blood vessels grow out from the choroid and into the retina. The process, known as choroidal neovascularization, is displayed in Figure 1. Initially, the vessels penetrate Bruch's membrane and grow under the RPE layer. Since the vessels are partially obscured by the RPE cells, this presentation is referred to as occult neovascularization. Further penetration, through the RPE layer, is referred to as classic neovascularization.
Wet age-related macular degeneration is a serious condition that can rapidly lead to blindness. The new vessels leak and bleed, which damages the retina and causes retinal detachment. Some patients with wet age-related macular degeneration present with complaints of a sudden onset of greatly diminished vision. Others, with no initial ocular symptoms, are diagnosed by ophthalmologic examination. Risk factors include age, family history, smoking, race, sunlight exposure, and cardiovascular disease and/or hypertension.
As noted above, there are 500,000 new cases of wet age-related macular degeneration each year in the developed world, and this incidence is increasing dramatically.