Repetitive, selective angiography of individual vessels of the retina

Recent experiments have shown the feasibility of using laser or microwave energy for the externally controlled release of both dyes and drugs from temperature-sensitive liposomes (lipid vesicles). In the present study, calcein, a fluorescent dye, was used to improve the in vivo capabilities of this controlled release system. In vitro studies showed that the encapsulation efficiency was improved when compared to carboxyfluorescein, the fluorescent dye used previously. The improved liposome and dye system was used to obtain repetitive, "selective angiograms" in isolated segments of the retina in rabbits and in a nonhuman primate (Macaca mulatta) over a period of up to 2 hours after a single liposome injection. Conventional fluorescein angiography of the primate retina one week after the end of the experiments showed no visible damage, even after more than 400 individual laser exposures.