Retinal vessel responses to passive tilting

Alterations in retinal vessel calibre on changing posture may indicate an autoregulatory response to changing perfusion pressure. The effect of passive tilting on retinal response in healthy individuals was investigated. Subjects were supported on a specially constructed tilting table. The control measurements were taken with the body in a 30 degrees head up position. Red-free fundus photographs were taken before, during and after a three minute period of 30 degrees head down tilting. Ten subjects were assessed (mean age 29 years: range 18-38). A total of 92 arteriolar and 86 venular sites were measured. On tilting to the head down position arterioles showed an early and significant decrease in calibre: mean -3.1% (p less than 0.001). Venules showed an increase of 3.7% (p less than 0.001). The response was not sustained throughout the period of tilting despite a maintained increase in ocular perfusion pressure, which was estimated in six of the subjects.