OCULAR VASCULAR THROMBOSIS FOLLOWING TIN ETHYL ETIOPURPURIN (SNET2) PHOTODYNAMIC THERAPY - TIME DEPENDENCIES

BACKGROUND AND OBJECTIVES: To evaluate the optimal time from the end o f photosensitizer injection to the commencement of light application f or creating characteristic fundus lesions and the time to vascular occ lusion following photodynamic therapy (PDT) with tin ethyl etiopurpuri n (SnET2). MATERIALS AND METHODS: Following intravenous injection of S nET2 0.5 mg/kg or lipid emulsion alone, the fundus of rabbits was irra diated at different times (5 to 240 minutes) after photosensitizer inj ection using 664 +/- 7-nm laser light with an irradiance of 354 mW/cm( 2) and fluence of 20 J/cm(2). Ophthalmoscopy and fluorescein angiograp hy were performed 1 day after SnET2 PDT. In separate groups of rabbits , treated areas of the fundus were imaged within 30 minutes following PDT using fluorescein vesicle and microsphere angiography with scannin g laser ophthalmoscopy to document time of vascular occlusion. All ani mals were killed 1 day following treatment and eyes were examined by h istopathology. RESULTS: Areas of hypofluorescence (indicating vascular occlusion) were seen when activating laser light was applied 5 to 20 minutes after SnET2 injection. Retinal vessels remained perfused in al l cases. The time to vascular occlusion was 70 to 120 and 40 to 30 min utes in nonpigmented and pigmented rabbits, respectively. No safety is sues were seen. CONCLUSION: PDT with SnET2 was effective in occluding the choriocapillaris. Activating light needs to be applied within a sp ecific time frame after photosensitizer injection to achieve vascular occlusion.