Encapsulation of sodium fluorescein for dye release studies

Recent investigations have detailed a selective dye release technique in which a pulse of laser light induces the release of a fluorescent dye from temperature-sensitive liposomes circulating in the retinal vasculature. This dye release technique has made possible a new method for measuring ocular blood flow in the retina and has spurred the development of repetitive, site-specific angiography. However, sodium fluorescein, the dye employed clinically for angiography of the retina, has not been employed in the aforementioned studies because of its rapid efflux from liposomes. This report outlines a method for stable encapsulation of sodium fluorescein in temperature-sensitive liposomes. Heat-induced leakage of the dye from liposomes in vitro was similar to that previously seen with other fluorescent dyes. Furthermore, after intravenous injection of encapsulated fluorescein in a nonhuman primate, dye released by a pulse of laser light allowed excellent visualization of the retinal architecture. These results indicate that sodium fluorescein, a dye that has proven to be the agent of choice for sensitive detection of leakage of vessels of the retina, can be released at a specific site in the retinal vasculature. Direct comparisons of the diagnostic capability of free and encapsulated sodium fluorescein are now possible.