Immediate response of retinal vessels to isometric muscle contraction.

Isometric muscle contraction results in a rise in systemic blood pressure (BP) and constriction of retinal arterioles. The responses in the anaesthetised cat have been studied to provide further insight into the results of human studies. Constriction (median 3.43% of control values) and dilatation (median 4.17% of control values) were observed; the onset of constriction was delayed by 4 s compared with dilatation. There was spatial and temporal variation in the observed calibre changes, and inter-experimental variation in the calibre change/BP ratio. It is concluded that the response of retinal arterioles of measurable size is not unified, and that the two modes of response differ in mechanism.