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July 2001

Increasing the Efficiency of Photodynamic Therapy in the Treatment of Subretinal Neovascularization

Arch Ophthalmol. 2001;119(7):1086. doi:

Photodynamic therapy has become a treatment modality for exudative age-related macular degeneration with classic subfoveal neovascularization, one of the most frequent causes of visual loss to and beyond the level of legal blindness in Western countries.

As shown by Schmidt-Erfurth and colleagues,1 a major problem with photodynamic therapy is the necessity to re-treat many patients for the recurrence of subretinal neovascularization. However, it may not be advisable to increase laser energy to permanently destroy subretinal neovascularization during the first treatment session because of the negative phototoxic and photothermic effects on the retinal pigment epithelium and photoreceptors. Because of the active perfusion of the subretinal neovascular membrane during laser coagulation, some of the laser energy needed for coagulation of the vessel is transported away from its required site of action. The question arises whether the efficiency of photodynamic therapy might be increased by reducing or even halting the bloodstream in the neovascular membrane during treatment. This may be achieved by artificially increasing the intraocular pressure using a suction cup applied to the surface of the conjunctiva.2 Choroidal blood perfusion is markedly dependent on the actual intraocular pressure, and may be close to zero at a level of 50 mm Hg or higher.3 Ischemic damage caused by a short-term elevation of intraocular pressure is not probable; experimental studies have shown that retinal ischemic tolerance time may be longer than 100 minutes.4

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