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A series of pathologic changes in the macula accompanied by decreased visual acuity.
Immediately beneath the sensory retina lies a single layer of cells called the retinal pigment epithelium. These cells provide nourishment to the portion of the retina in contact with them—the photoreceptor cells that contain the visual pigments. For unknown reasons, maintenance of this contact is threatened in the macula of the aging eye. A disruption of this contact between the retinal pigment epithelial cells and photoreceptor cells results initially in distorted vision and eventually in a loss of central visual acuity. Two major processes in the macula can disrupt the retinal pigment epithelium-sensory retina interface.
A small hemorrhage may break through the retinal pigment epithelium from the underlying choroid, which contains a rich vascular bed. Blood accumulates between the retinal pigment epithelium and the sensory retina, and if bleeding resolves quickly, no permanent harm results. However, if new blood vessels grow from the choroid into the clot, they will continue to leak, causing more separation of the retinal pigment epithelium-sensory retina interface. This disrupts the nourishment of the photoreceptor cells and leads to their death, resulting in a loss of central visual acuity. This type of age-related maculopathy is called the wet type because of the leaking vessels and the edema or blood that detaches the sensory retina from the retinal pigment epithelium. The dry type of age-related maculopathy involves disintegration of the retinal pigment epithelium and a secondary loss of the overlying photoreceptor cells resulting from nutritional loss. The wet type accounts for only 10% of age-related maculopathy cases but results in 90% of cases of legal blindness (visual acuity of 20/200 or less) from macular degeneration in the elderly. The dry type reduces vision but usually only to levels of 20/50 to 20/100.
Symptoms, Signs, and Diagnosis
The patient may notice that central vision is distorted as objects appear larger or smaller, or straight lines appear distorted, bent, or without a central segment. If central vision is distorted in only one eye, the patient is unlikely to notice any change in vision. However, if the patient views a grid of fine lines with each eye alternately, distortion can be quickly detected. Therefore, those considered at high risk for age-related maculopathy are given a grid to view each morning. Following the onset of distortion, visual acuity may decrease, possibly within days.
In the wet type, a small detachment of the sensory retina may be noted in the macular area, but the definitive diagnosis of a subretinal neovascular membrane requires fluorescein angiography. In the dry type, drusen may disturb the pigmentation pattern in the macular area. Drusen are excrescences of the basement membrane of the retinal pigment epithelium that protrude into the cells, causing them to bulge anteriorly. Through the ophthalmoscope, they appear as small, rounded, yellow-white areas with indistinct borders. Their specific role as a risk factor in age-related maculopathy is still unclear.
Treatment
No treatment is known for the dry type of age-related maculopathy. But laser treatment initially obliterates the neovascular membrane in the wet type and prevents further visual loss in about 50% of patients at 18 mo. By 60 mo, however, only 20% show a substantial benefit. High-risk patients (eg, those who have age-related maculopathy in one eye or a family history of the condition) should view a grid daily to detect early distortion in central vision that could benefit from early laser treatment.
Although patients who have decreased central visual acuity cannot read or drive a car, they can continue to perform many everyday activities. The remainder of the sensory retina is unaffected in these patients, so they can be assured that they will not become completely blind.
For near-vision tasks (eg, reading and watching television), magnifying lenses and high-intensity lighting matched for daylight are often helpful. A telescopic lens may help the patient identify street signs and perform other visual tasks that facilitate travel. Some optometrists and ophthalmologists specialize in fitting such optical aids.

This entry was posted on Sunday, April 19th, 2009 at 1:40 pm and is filed under Health. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.