Photodynamic Therapy for Wet Macular Degeneration
Photodyanamic therapy (PDT) is the latest treatment for choroidal neovascular membranes (CNVM), which are the leaky vascular structures under the retina in the "wet" form of age related macular degeneration (AMD).
PDT utilizes an innovative idea to treat CNVM's without damaging overlying or nearby retinal or other ocular tissues.
The Photodynamic Therapy Procedure
In Photodynamic therapy, a photosensitive dye known as Visudyne (verteporfin) is administered intravenously (IV) and allowed to perfuse the CNVM, as well as the remainder of the body. Then the ophthalmologist treats the CNVM with a red laser of a specific wavelength (689nm) for about 90 seconds. The non-thermal laser light activates the Visudyne producing an active form of oxygen that both coagulates and reduces the growth of abnormal blood vessels. This, in turn, inhibits the leakage of fluid from the CNVM.
In the FDA studies involving "wet" macular degeneration and treatment with PDT, patients had initial vision between 20/40 and 20/200. Treatment was also limited by the size of the lesion. Furthermore, this treatment was utilized only for new CNVM's. Old scars of the retina were not treated.
What to Expect After Photodynamic Therapy
The results of the FDA studies showed that 70% of patients had stabilization of their vision with treatment and 14% had visual improvement. As such, one might expect that the better the initial vision, the better the final outcome with treatment. Finally, an average total of 3.4 treatments were administered during the first year of follow up, and 2.1 treatments in the second year of follow up. Thus, an average total of 5.5 treatments were needed in the first two years to maintain stabilization. As such, we might infer that this therapy is not a cure and does not usually result in improved vision, rather, the effect is more a stabilization of vision.
Because Visudyne acts as a photosensitizer, the effect of sunlight (or ultraviolet light) on the eyes and skin may be greatly enhanced. Therefore, patients should avoid exposure to sunlight for 5 days following PDT to prevent potentially severe sunburn.
The results of PDT with Visudyne are very promising, and certainly should be considered in any patient with new onset "wet" macular degeneration. However, patients with long standing "wet" macular degeneration which has led to scarring are unlikely to benefit. Patients must have realistic expectations for this form of therapy, i.e., PDT is unlikely to restore vision that has already been lost due to AMD.