In diabetic maculopathy, fluid rich in fat and cholesterol leaks out of damaged vessels. If the fluid accumulates near the center of the retina (the macula) as indicated by the black pointer there will be distortion of central vision. If too much fluid and cholesterol accumulates in the macula, it can cause permanent loss of central vision. CSME (clinically significant macular edema) is the term given to describe water logging of the macular area.
In diabetic retinopathy, the vessels become more permeable. Water, blood cells, proteins, fats, and other large molecules may leak out into the surrounding retinal tissue. Accumulation of this fluid in the central region of the retina (the macula) is called macular edema or diabetic maculopathy. Diabetic Maculopathy is the most common cause of decreased vision in patients with background or nonproliferative diabetic retinopathy. It is visible on examination as a thickening and slight graying of the retina, and is often associated with exudates (yellow clumps or spots within the retina). Exudates are the result of fats and proteins leaking out of the permeable vessels along with water. The water can be quickly reabsorbed into the vessels or into the tissue under the retina, but the fatty material is absorbed only very slowly. These fatty exudates are left behind like a "bathtub ring", often in a ring-like shape surrounding the leakage site.
This photograph of a retina shows multiple micro aneurysms (small arrowheads) and hemorrhages scattered through the macular region. There is an area of diabetic maculopathy to the left of center, with some associated yellow exudate (large arrowhead).
Swelling in the retina is fairly common in background diabetic retinopathy, but it is not always significant swelling. In other words, retinal edema does not always affect vision and does not always heat energy, producing a small burn. The most commonly used wavelengths in treatment of macular edema are in the yellow and green portion of the spectrum, since these wavelengths are best absorbed by hemoglobin. Red laser is also used occasionally. Macular laser treatments are usually painless. The burn produced by the laser creates a faint scar under the retina which usually is not noticed by the patient. It takes approximately one month to see the effect of the laser treatment (decreased edema and improved vision), although it may occur within a few days or take as long as several months.
Complications of macular laser do occur, but they are unusual. The most feared complication is accidental laser treatment of the center of the macula, which can cause marked permanent decrease in vision. Fortunately, this complication is quite rare. A more common complication is an increase in the macular edema lasting several days to weeks following the laser treatment. Although the decreased vision in these cases is annoying, it usually resolves spontaneously.
Diabetic maculopathy is often described as being either focal or diffuse, and treatment of the edema is specific to the type. Focal macular edema is swelling due to leakage from a few specific spots in the retina, usually leaking micro aneurysms or dilated retinal vessels. Treatment of focal macular edema is done by coagulating the individual micro aneurysms or leaking vessels in order to stop the leakage. A 50-100 micron spot of laser is applied to the micro aneurysm with sufficient power to produce whitening or coagulation. Diffuse macular edema is caused by leakage from multiple retinal vessels as well as from the pigmented cells under the retina. It would be impossible to treat all areas of leakage in a case of diffuse edema. Instead, a grid pattern of laser spots are placed around the center of the macula. The mechanism by which grid laser treatment works is unknown, but may have to do with destroying abnormal pigmented cells and allowing more normal cells to replace them.
The efficacy of laser treatment for macular edema (diabetic maculopathy) has been documented in large multi-center clinical trials. The ETDRS was the largest of these trials. It showed that eyes with clinically significant macular edema that did not receive laser treatment were twice as likely to have severe loss of vision as compared with similar eyes that received laser treatment. These results indicate that treatment of macular edema should be based on the location and severity of the edema, not necessarily on the visual acuity. |
