[Observation of erythrocyte flow in retinal vessels during fluorescein angiography]

Erythrocytes do not take up fluorescein intracellularly during angiography, they are hypofluorescent compared to blood plasma. This negative staining phenomenon has not been observed in the human retina. Scanning Laser Ophthalmoscopy permits imaging of the retina with a higher temporal and a higher spatial resolution than a conventional funduscamera. Thus, the retinal erythrocyte flow can be observed during fluorescein angiography. The red blood cells are seen as multiple black dots in a superficial layer of the intravasal blood column. A pathologically reduced blood flow can be recognized by simple observation. The velocity of the red blood cells is estimated with an erythrocyte velocimeter, that permits an optical comparison between the velocity of black dots and the velocity of the cells in the retinal vessel. The measured values fit well to the data obtained with the laser doppler technique. Therefore, the negative staining phenomenon in association with scanning laser ophthalmoscopy gives us a new tool in retinal microcirculation research.