Determination of retinal blood velocity with respect to the cardiac cycle using laser-triggered release of liposome-encapsulated dye.

A system of selective angiography has been developed for measuring blood velocity in retinal arteries and veins. It uses a liposome-encapsulated fluorescent dye that is released by application of laser energy in a specific retinal vessel. The method is shown to be able to distinguish between peak systolic velocity and minimum diastolic velocity. In the cynomolgus monkey, the two values were found to differ by approximately a factor of three. It is known that many ocular and systemic diseases affect retinal circulation, and therefore a method of blood velocity measurement with such sensitivity may prove highly valuable in the practice of ophthalmology. As an example, the velocity in a retinal vein was measured before and after partial occlusion by photocoagulation. The two values obtained were significantly different, and the blood velocity was found to return to the value prior to occlusion when measured at 18 days.