Photodynamic therapy (PDT) is a type of laser treatment initially approved for use in the treatment of wet age-related macular degeneration (AMD). While the first line treatment for wet AMD now consists of medication injections directly into the eye, PDT is still sometimes used in combination with these therapies. PDT is also used in the treatment of central serous chorioretinopathy (CSCR), polypoidal choroidal vasculopathy (PCV), and choroidal hemangioma.
PDT is a non-thermal or "cold" laser. Unlike the lasers used in retinal photocoagulation, which use thermal energy to create burns in the retina, PDT uses a laser to activate medication given intravenously. Verteporfin is a medication given through an IV. The medication travels throughout the blood stream into the choroid, which lies behind the retina. The choroid is where the abnormal blood vessels of wet AMD originate, and it is also the source of abnormal activity in other diseases such as CSCR, PCV and choroidal hemangioma. The PDT laser activates verteporfin in the region of abnormal blood vessels, thereby closing off the abnormal blood vessels and reducing the leakage of blood and fluid into the space between the retina and choroid.