Experimental photodynamic effects of hypocrellin A on the choriocapillaris.

OBJECTIVE To investigate the use of the photosensitizer hypocrellin A as a photodynamic agent to occlude the choriocapillaris in the eyes of pigmented rabbits. METHODS Hypocrellin A (500 microg/kg) incorporated into liposomes was injected intravenously in pigmented rabbits. Ten to 15 minutes later, the retinas were irradiated with a dye laser (spot size, 2 mm; 10-60 mW; 10-60 seconds; fluences 3.2 to 95.5 J/cm2) at two wavelengths: yellow (568 nm) and red (647 nm). Fluorescein angiography was performed 2 and 24 hours later. Parallel controls were irradiated without a photosensitizer. Histology was performed immediately after the 24-hour angiogram. observed 24 hours after PDT in eyes subjected to yellow laser irradiation at 20 mW for 60 seconds (fluence, 38.2 J/cm2) and at higher powers for lesser durations: 30 mW for 40 seconds (fluence, 38.2 J/cm2), 40 mW for 20 seconds (fluence, 25.4 J/cm2), and 50 and 60 mW for 10 seconds (fluences, 15.9 and 19.1 J/cm2, respectively). Light microscopy showed occlusion of the choriocapillaris in all eyes with angiographic responses. Control eyes and eyes irradiated with the red laser revealed no angiographic or histologic changes. CONCLUSION Photodynamic therapy using liposomal hypocrellin A and the yellow laser of 568 nm was effective in occluding the choriocapillaris of pigmented rabbits.