[Fluorescence angiography image of erythrocytes with the scanning laser ophthalmoscope].

Erythrocytes bind fluorescein to their surface, but they do not take up the dye intracellularly during fluorescein angiography. The cells are therefore hypofluorescent compared to blood plasma. Due to the high velocity of red blood cells in retinal vessels, this phenomenon has not been observed during conventional angiography. Scanning laser ophthalmoscopy, however, allows imaging of the retina with a very high temporal resolution. The exposure time of the scanning laser beam for a single erythrocyte is in the range of only 100 ns. Therefore, scanning laser ophthalmoscopy permits imaging of fast-moving red blood cells in large retinal vessels. Pathologically reduced blood flow is clearly visible and can be measured with digital image analysis. The values found in three patients with vascular occlusions were between 0.1 and 1.8 mm/s. In cases with intact circulation, digital image analysis was not sufficient to measure red blood cell velocity. Even if a velocimeter that permits semiquantitative comparison between erythrocytes and moving black dots is used, superimposed on the angiogram, reliable results can only be obtained in cases with reduced red cell velocity. Nevertheless, for the clinician observation of erythrocyte flow during scanning laser angiography is a new and fascinating tool.