Autoregulation of blood flow in the capillaries of the human macula.

The entoptic phenomenon by which one can observe leukocytes flowing in one's own parafoveal capillaries has been used to study the effect of changes in perfusion pressure on blood flow. Our measurements in humans with normal ocular fundi indicate that the retinal circulation of the parafovea is autoregulated in relation to perfusion pressure. The average time lag between a change in blood flow and the beginning of the autoregulatory response was about 46 sec., and the average duration of this response was about 48 sec. At the end of the autoregulatory response, the vascular resistance of the parafoveal segment was about 50% lower than that at normal intraocular pressure.