The scanning laser technique in combination with digital image analysis allows direct objective measurement of flow velocities in perimacular capillaries. In addition, the complete macular network of capillaries can be observed. By means of digital frame-to-frame picture analysis of digital recordings, blood flow velocities and morphologic data have been measured. The mean flow velocity in perimacular capillaries observed with the scanning laser ophthalmoscope in healthy subjects (n = 21) amounted to 3.28 +/- 0.45 mm/second. In patients (n = 13) with diabetes mellitus (no or background retinopathy), the mean flow velocity was significantly reduced (2.89 +/- 0.57 mm/seconds) compared with healthy subjects. Morphologic data of the perifoveal capillary bed showed a significant reduction of capillaries in patients with diabetes mellitus when compared with healthy subjects.