PhotoDynamic Therapy (PDT) was a weapon developed in 1990 in the armamentarium against choroidal subretinal neovascularization (CNVM). One needs to understand the mechanism of action of this new therapy, its true benefits and its true limitations.
PDT is an innovative idea in treating new vessel membranes (CNVM) and scar tissue under the retina. A photosensitive dye is injected into the arm of the patient and allowed to perfuse the CNVM (as well as the rest of the body). A special "cold" laser is then used to activate the dye at a very specific wavelength (689 nm) theoretically treating only the CNVM and not the surrounding retina and RPE. The laser is called "cold" because it does not burn or cauterized tissues as do conventional lasers.
Several studies are underway evaluating different dyes and wavelengths, however the FDA recently released Visudyne (verteporfin dye) for use in AMD. In a two year study it was shown that in patients with subfoveal (under the center part of vision) CNVM of a specific type (>50% "classic" CNVM) could benefit from this treatment. In the study patients had visions from between 20/40 and 20/200 with the above requirement. Treatment was also limited by the size of the lesion and that the lesion had to be of recent onset (not for old scars).
The results of this study showed that 70% of patients had stabilization of their vision with this treatment and 14% had visual improvement. It should be emphasized that the 70% with stabilization were just that--the patients had less reduction in vision than did patients not receiving verteporfin. Someone with 20/40 vision might then expect to retain better vision than someone starting with 20/200 vision. Also, on average 3.4 treatments were necessary in the first year and 2.1 treatments in the second year to maintain stabilization. In other words the average patient might expect to require treatment 5-6 times in the first two years. This therapy does not cure the problem or afford most patients a chance at improvement, only stabilization of the vision. After injection of the dye, patients are required to stay out of sunlight or halogen light for five days to avoid severe "sunburn".
Other studies of PDT (now called OPT by some for Ocular Photodynamic Therapy) showed a beneficial effect of treatment of ill-defined membranes by 24 months after treatment and a definite beneficial effect in subretinal membranes caused by myopia.
RVT participated as one of the study centers for PDT and has extensive experience in its use. In the proper patient it certainly can help to retain vision and should be considered another of a group of treatments for AMD. PDT has mostly been supplanted by the use of anti-VEGF medications (See AMD).
Disclaimer Stuff: The opinions expressed in this website are those of RVT. Diagnosis and therapy should be based on a thorough examination by and recommendations of a qualified eye provider.