There are two basic types of macular degeneration: "wet" and "dry." Approximately 10-15% of the cases of macular degeneration are the "wet" (exudative) type.
In the "wet" type of macular degeneration, abnormal blood vessels (known as choroidal neovascularization or CNV) grow under the retina and macula. These new blood vessels may then bleed and leak fluid, causing the macula to bulge or lift up from its normally flat position, thus distorting or destroying central vision. Under these circumstances, vision loss may be rapid and severe.
What the Patient may see:
With the "wet" type, patients may see a dark spot (or spots) in the center of their vision due to blood or fluid under the macula. Straight lines may look wavy because the macula is no longer smooth. Side or "peripheral" vision is rarely affected. However, some patients do not notice any such changes, despite the onset of neovascularization (1). Therefore, periodic eye examinations are still very important for patients at high risk.
For a video presentation describing what a person with macular degeneration sees,
Two Forms of Choroidal Neovascularization
There are two forms of choroidal neovascularization (CNV) that have been identified, "classic" and "occult." The classic form is well-defined and usually results in vision that is between 20/250 and 20/400, but it may be worse than 20/800. For eyes with the occult form, the average visual acuity is somewhat better, between 20/80 and 20/200. Occult lesions are not well-delineated and they have less leakage (2).
Once CNV has developed in one eye, whether there is a visual loss or not, the other eye is at relatively high risk for the same change. When all four risk factors—more than five drusen, large drusen, pigmental clumping, and systemic hypertension—are present, the five-year risk of CNV in the second eye is 87%, whereas if none of these risk factors are present, the risk is 7% (3).
In addition, CNV may progress rapidly, and any sudden change in central vision therefore requires a prompt examination after dilation of the eyes. The purpose of this exam is to find out whether the sudden loss of vision is due to leakage of blood vessels and which treatment may be appropriate.
For a video presentation illustrating the development of macular degeneration,
1. AM Fine, Earliest symptoms caused by neovascular membranes in the macular. Arch Ophthal. 1986;104:513-4.
2. MG Maguire, Natural history. JW Burger, SL Fine, MG Maguire, eds. Age-related Macular Degeneration. St. Louis: Mosby: 1999;17-30.
3. Macular Photocoagulation Study Group. Risk factors for choroidal neovascularization in the second eye of patients with juxtafoveal or subfoveal choroidal neovascularization secondary to age-related macular degeneration. Arch Ophthal. 1997;115:741-7.