Porphyrins are dyes which react with light to close abnormal blood vessels.
For treatment, a porphyrin dye is injected into the patient's vein. 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. 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. Side effects have included discomfort, swelling, pain or bleeding at the injection site.