Porphyrin - Laser

Photodynamic Therapy (PDT)

Porphyrins are dyes which react with light to close abnormal blood vessels. For treatment, a porphyrin dye is injected into the patient's vein. After the dye travels into the abnormal subretinal blood vessels, a "non-heat-producing" laser is focused on this tissue causing the dye to activate, releasing a substance that damages (closes) the abnormal leaking blood vessels.

In an International prospective controlled clinical trial, vision was stable or improved in 61.4% of patients treated with the porphyrin dye - laser technique after 1 year follow-up.

In comparison, the "placebo" or untreated control group of patients were noted to be stable or improved in 45.9% of cases. That is,there was a 15.5% difference between treatment and no treatment after 12 months follow-up.

Treatments may need to be repeated every 3 months to keep the leaking from the abnormal blood vessels from reappearing on the fluorescein angiogram and damaging the retina.

Like standard "heat producing" lasers, the abnormal blood vessels must be visible (not covered by blood, fat, or fluid) in order to work and the growth of neovascularization must not be too large. In general, photodynamic therapy worked best for patients with >50% "classic" neovascularization.

Recent studies have also suggested that Visudyne treatment reduces the risk of moderate vision loss for patients presenting with purely occult neovascularization. 55% percent of Visudyne treated patients lost 3 or more lines of visual acuity compared to 68% of patients who received placebo (after 2 years of follow up). At 2 years, the risk of severe visual loss was diminished by 18%. It is important to note that though these are significant improvements, many patients can continue to lose vision despite treatment.

Treatment: Usually requires a slow (ten minute) infusion of the dye, followed by a 1-2 minute application of laser-light. Treatment usually causes the abnormal vessels to temporarily stop or decrease their leaking. PDT treatment may have to be repeated every three months up to 3 to 4 times during the first year.

Potential problems associated with treatment with visudyne have included injection site reactions, headaches, blurring, decreased sharpness and gaps in vision, and in 1-4% of patients a substantial decrease in vision with partial recovery in many patients. Patients should avoid direct sunlight for 5 days to avoid sunburn. People with porphyria should not be treated.

We must congratulate the patients and health-care professionals who participated in this scientific study.

 

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An Opinion About Photodynamic Therapy

 

Novartis Ophthalmics makes Visudyne Dye.

 

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