by Dan Roberts
Drusen are thought to be fatty waste products from the photoreceptor cells. They often appear on the macula (the center of the retina) in the early stages of Macular Degeneration, and they can cause gradual loss of central vision. “Hard” drusen are common in aging eyes, and do not necessarily lead to MD. Irregular and ill-defined “soft” drusen,” however, often indicate problems in the near future.
In 1999, ophthalmologists took an interest in using the laser to destroy drusen, based upon the theory that ridding the retina of these deposits may slow the development of MD, or even stop the progression from the “dry” form to the “wet” form. Studies were conducted at the University of Michigan School of Medicine and the University of Pittsburgh, and continued until 2005. Called “Complications of AMD Prevention Trial” (CAPT) and Prophylactic Treatment of AMD” (PTAMD), they used low-intensity lasers on human volunteers in the early stages of MD.
A grid pattern was lasered around the macula of patients with high-risk large drusen in both eyes. One treatment (funded by the National Eye Institute) used a low-intensity argon laser, and the other used an infrared diode laser. After two years, researchers using the latter procedure reported a significant reduction in the number of and area occupied by drusen and significant improvement in the subjects’ visual acuity. (Olk RJ, Friberg TR, Stickney KL, et al. “Therapeutic benefits of infrared (810-nm) diode laser macular grid photocoagulation in prophylactic treatment of nonexudative age-related macular degeneration.” Ophthalmology. 1999;106:2082-2090.
Later, however, in a presentation to the 2002 ARVO convention (“Prophylactic Treatment of Age-Related Macular Degneration (PTAMD): Update on the Clinical Trial”), researchers reported that prophylactic subthreshold laser treatment of a patient already having AMD in one eye showed no beneficial effect in preventing choroidal neovascularization (CNV), and the procedure may actually promote CNV events and vision loss, at least in the short term. At the same time, it was determined that patients who had drusen in both eyes, but no occurences of CNV may or may not benefit from prophylactic subthreshold laser treatment.
Finally, in April 2006, Friberg et al reported that laser treatment “to an eye with multiple large drusen in a patient whose fellow eye has already suffered a neovascular event places the treated eye at higher risk of developing choroidal neovascularization.” They concluded by advising against using prophylactic subthreshold diode laser treatment in these eyes.
For the full report, see “Prophylactic treatment of age-related macular degeneration report number 1: 810-nanometer laser to eyes with drusen.” (Friberg TR, Musch DC, Lim JI, Morse L, Freeman W, Sinclair S; PTAMD Study Group, Department of Ophthalmology, University of Pittsburgh, Pittsburgh, Pennsylvania 15213, USA.)
A few months later, on November 1, 2006, the National Eye Institute announced that their CAPT studies have been small, and the results inconsistent. No difference in vision or in progression to advanced AMD between treated and untreated eyes were observed, so doctors are advised to reconsider drusen lasering as a treatment for AMD.