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In PDT, a dye that reacts to light is injected into the patient's arm. As the dye moves up to the eye and passes through the body, it pools in those damaged new blood vessels of the retina.

A laser with a low power (a cold laser) is used. When the dye is exposed to the laser, it seals off the leaking vessels. Since the dye does not stay in the healthy retinal cells, they do not react to the laser and are not damaged.

However, since the dye remains in the body for several days, patients must stay out of the sun and cover up carefully on their trip home from the ophthalmologist or they will get a severe sunburn. Otherwise, few side effects or complications have been reported and the treatment is quite successful for selected patients.