Diode laser-induced thermal damage evaluation on the retina with a liposome dye system

Background and Objectives The aim of the study was to evaluate the feasibility of retinal thermal damage assessment in a rabbit eye model by using laser‐induced release of liposome‐encapsulated dye. Study Design/Materials and Methods After anesthesia, thermosensitive liposomes (DiStearoyl Phosphatidyl Choline: DSPC) loaded with 5,6‐carboxyfluorescein were injected intravenously to pigmented rabbits. Retinal photocoagulations were performed with a 810nm diode laser (P=100–400 mW, Ø=500 μm, 1s) (OcuLight®, IRIS Medical Instruments, Mountain View, CA). Fluorescence measurements in the area of the laser exposures were then realized with a digitized angiograph (CF‐60UVi®, Canon‐Europe, The Netherlands ; OcuLab®, Life Science Resources,® UK). Results Fluorescent spots were observed for power ranging from 100 ± 5 mW to 400 ± 5 mW. The fluorescence intensity increased linearly with the power and reached a plateau at 280 ± 5 mW. The fluorescence intensity was correlated to the maximum temperature at the center of the laser spot with a linear increase from 42 ± 3°C to 65 ± 3°C. These results are in agreement with our two previous studies with DSPC liposomes for temperature measurements in a tissue model and then in a vascular model. Conclusion This preliminary study demonstrates the possibility of a laser‐induced release of liposome‐encapsulated dye for a quantification of diode laser induced thermal damage in ophthalmology. Such a method could be useful for a real‐time monitoring of laser photocoagulation for conditions such as choroidal neovascular membranes when a precise thermal damage is required near the foveolar area. Lasers Surg. Med. 24:61–68, 1999. © 1999 Wiley‐Liss, Inc.