Measurement of retinal blood velocity and flow rate in primates using a liposome-dye system

A recently developed liposome-dye method was used to make quantitative measurements of blood velocity and volumetric flow rates in the retina of the rhesus monkey. After systemic injection of a liposome-encapsulated fluorescent dye (calcein), the release of a bolus of the dye in the retina was triggered by an ophthalmic argon laser. Initially, calcein was entrapped at a high concentration and the fluorescence of the dye in the lipid vesicle was quenched. After laser exposure, the liposomes released a bolus of dye at the laser exposure site in a specific vessel of the retina. The released dye formed a well-defined, fluorescent wavefront in the exposed artery or vein. By measuring the distance the dye traveled in the vein over a set time interval, it was possible to measure blood velocity in retinal vessels of various diameters, and to calculate volumetric flow rates in those vessels.