Photodynamic Therapy (PDT) is a procedure where a light-activated drug called Visudyne (verteporfin) is given intravenously, and a specially designed laser is used to close the abnormal vessels while leaving the retina intact. You may need several treatments over one to two years because closed blood vessels can reopen within the treated area. Because Visudyne is activated by light, exposure to sunlight must be avoided for five days after treatment. This laser treatment uses a broad beam of laser light covering the entire macula and is vastly different from the more standard Argon laser treatment where the surgeon precisely controls the laser light to cauterize specific leaking vessels under the slit-lamp.