Verteporfin (Visudyne) - Lasers, free radicals, and fixing people's eyes

• macrocyclic porphin-derived photosensitizer used as part of ocular photodynamic therapy (PDT) for the treatment of ocular diseases that feature choroidal neovascularization (CNV), a major cause of vision loss
• the choroid is a layer of the eye (between the sclera and the retina) that contains lots of blood vessels
• CNV is the abnormal growth of blood vessels from the choroid toward the retina, where seeing takes place, and is associated with a number of eye diseases including age-related macular degeneration (AMD, deterioration of the central part of the retina), pathological myopia (abnormal changes in eye structure causing vision problems), and ocular histoplasmosis (a crazy-ass fungal infection of the eye)
• administered intravenously, then once it reaches the choroidal circulation and begins hanging out in the aberrant vessels there, a nonthermal red laser light (wavelength of 693 nm, natch) is shone on the afflicted eye, resulting in the activation of the drug
• verteporfin is a highly conjugated molecule, which enables it to effectively absorb light and, if in the presence of oxygen, transfer the radiant energy to oxygen atoms, producing radical oxygen species (ROS) like singlet oxygen and superoxide, which then go about and wreck havoc on the bad vessels both directly and via platelet activation with thrombosis and vessel occlusion
• since it's modus operandi is to cause temporary photosensitization, patients have to avoid exposing their skin or eyes to direct sunlight or even very bright indoor light for 5 days after being dosed with verteporfin, or else the drug will be activated where it shouldn't be and a severe reaction featuring things like blistering, burning, and swelling will develop at the sites of light exposure
• PDT with verteporfin may also work on corneal neovascularization
  

Yoon KC et al. Photodynamic Therapy with Verteporfin for Corneal Neovascularization. Am J Ophthalmol. 2007 Jul 12; [Epub ahead of print]
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