The chorioretinal damage caused by different half parameters of photodynamic therapy in rabbits

Purpose: To compare the chorioretinal tissue response after different half-strength parameters of photodynamic therapy (PDT) in rabbits.

Methods: The study included 4 groups, and each group contained 4 animals. The full dose served as the control group: verteporfin (4mg/kg) with 600mW/cm² irradiance from a diode laser at 689nm applied to the retina for 8s. One parameter was changed to half-strength in the other 3 groups. The HLaser group received half-strength laser irradiance. The HTime group was exposed to photosensitization for half the time, and the HDose group received half the drug dose. Six laser spots were generated in each of the eyes of every rabbit and documented graphically. The lesions were examined on days 1, 7, and 42 after PDT treatment using color fundus imaging, fluorescein angiography (FA), and histopathology analysis.

Conclusions: Among these PDT parameters, decreasing the laser irradiance by half showed the greatest decrease in chorioretinal damage in an experimental animal model.

Results: PDT treatment in rabbits caused chorioretinal damage in all 4 groups. FA on day 1 showed that the use of half the laser irradiance, half the drug dose, or half the photosensitizing time tended to decrease the damage to the chorioretinal tissue in terms of the number of occlusions and the area of occlusion, but only the results from half the laser irradiance were significantly different. In addition, the HLaser and HDose groups showed significantly less apoptosis by TUNEL staining on day 1.