Update on Ocular Photodynamic Therapy (PDT)
June 2001
We began using Visudyne for OPT at Carolina Retina Center, P.A. in the fall, 1999, as investigators in an expanded access protocol. The treatment was subsequently approved in April, 2000. It has now been a year since the FDA approval of Visudyne for OPT and we are pleased that we have an effective new weapon against choroidal neovascularization.
The treatment involves a 10 minute timed IV infusion of the dye based on body surface area. The dye accumulates preferentially in the abnormal neovascular tissue. A washout period of five minute is given to minimize the risk to the normal retinal vessels. This is followed by an 83 second continuous application of a visible light, low power laser to activate the dye. The activated dye locally damages the vascular endothelium to create occlusions. This mechanism is designed to avoid the direct retinal damage that is always caused by thermal laser ablation. Since the dye is light activated, the patient must avoid direct sunlight or bright artificial lighting for 5 days.
Our experience has been very positive. Most patients have no problems with the infusion although an ache in the low back occasionally occurs. We are careful to avoid leakage of the dye since this can render the skin light sensitive for several weeks.
Our best data for OPT remains the TAP study published in October, 1999. This study demonstrated a treatment benefit for predominantly classic ( greater than 50% ) sub-foveal choroidal neovacular membranes caused by age related macular degeneration. In the treated group, 59% lost fewer than three lines of vision after two years compared with 31% of the placebo treated group. This benefit requires re-evaluation by fluorescein angiography at six to twelve week intervals with repeat treatment for persistent leakage. All patients had at least 20/200 visual acuity at the start.
We are starting to see data for OPT in other circumstance. The VIP study to compare treatment with placebo in occult disease has demonstrated a modest benefit with treatment. Preliminary data at two years reveals that 46% of treated patients lost less than three lines of vision compared with 33% of the placebo group. We are awaiting publication of the final results to learn how best to apply this treatment.
In a preliminary study of pathological myopia, the one year data revealed a 19% differential treatment benefit for OPT. Unfortunately, this declined to a 7% benefit in preventing 3 lines of visual loss after 2 years. However, there was a gain of at least three lines in 12% of the treated group and none of the placebo group. This gives some hope in an often devastating condition.
Preliminary data in ocular histoplasmosis syndrome also is available. An uncontrolled, open label study showed improvement in vision in 69% of cases. Although the natural history of these cases may be better than other causes of choroidal neovascularization, we are hopeful that this treatment is effective. Overall, we are pleased with our experience with OPT. It has opened a new realm of treatment for lesions that previously could not be helped. Currently, our local Medicare carrier only recognizes treatment in predominantly classic, subfoveal choroidal neovascularization caused by age related macular degeneration. As more data becomes available, we hope to see this expand. Although OPT does not cure the underlying disease process, it is beneficial in stabilizing vision in a significant number of our patients.
