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.
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