2020–2021 BCSC Basic and Clinical Science Course™
12 Retina and Vitreous
Part III: Selected Therapeutic Topics
Chapter 19: Laser Therapy for Posterior Segment Diseases
Photodynamic therapy (PDT) using the photosensitizing drug verteporfin is approved by the US Food and Drug Administration for treating certain types of subfoveal CNV in age-related macular degeneration and subfoveal CNV that is secondary to ocular histoplasmosis syndrome and myopia. Because more effective treatments have become available, PDT has generally fallen out of favor for the management of CNV, but it continues to be a valuable option for the management of some ocular tumors and central serous chorioretinopathy.
PDT is a 2-step procedure:
intravenous administration of the photosensitizing drug, which localizes to endothelial cells of vessels present in CNV and tumors
local activation of the drug by a laser wavelength preferentially absorbed by the sensitizing drug
The low-intensity laser energy produces a photochemical reaction, leading to the formation of reactive oxygen species and free radicals. These radicals cause endothelial cell damage, platelet adherence, vascular thrombosis, and capillary closure.
Complications of Photodynamic Therapy
The most serious adverse effects of PDT are photosensitivity reactions that range from mild to second-degree burns of sun-exposed skin. This can be avoided by having the patient minimize exposure to sunlight for 5 days after treatment. In the Treatment of Age-Related Macular Degeneration with Photodynamic Therapy (TAP) Study Group report, severe vision loss occurred in 0.7%–2.2% of patients within 7 days of PDT treatment of subfoveal lesions. Additionally, verteporfin infusion–related transient lower-back, side, and chest pain were reported in 2.0%–2.5% of patients. In efforts to minimize choriocapillaris nonperfusion and ischemia, treatment using half-fluence PDT (25 J/cm2 energy; 300 mW/cm2 light intensity) has become more common, and it may be as effective as standard-fluence PDT.
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.