FEASIBILITY OF LASER-TARGETED PHOTOOCCLUSION OF THE CHORIOCAPILLARY LAYER IN RATS

Purpose. A new method, laser-targeted photoocclusion, was developed to occlude choroidal neovascularization while minimizing damage to the o verlying retina. The ability to occlude normal choriocapillary layer i n rats was evaluated as a first test of the feasibility of treating ch oroidal neovascularization with this method. Method. A photosensitive agent, aluminum phthalocyanine tetrasulfonate, encapsulated in heat-se nsitive liposomes, was administered intravenously along with carboxyfl uorescein liposomes. A low-power argon laser (retinal power density of 5.7 W/cm(2)) locally released a photosensitizer bolus, monitored by t he simultaneous release of carboxyfluorescein. A diode laser (operatin g at 675 nm with a retinal power density of 0.27 W/cm(2)) activated th e photosensitizer with its release. Results. Vessels in the choriocapi llary layer were occluded at day 3 after laser treatment and remained unchanged during the 30-day followup. Larger choroidal vessels and ret inal capillaries remained perfused. Control experiments excluded possi ble effects of heat or activation of free photosensitizer. Pilot histo logic studies showed no damage to the retinal pigment epithelium. Conc lusions. Laser-targeted photoocclusion caused selective occlusion of n ormal choriocapillaries while sparing overlying retinal pigment epithe lium and retinal vessels. The method has potential as a treatment of c horoidal neovascularization that may minimize iatrogenic loss of visio n.