Scanning electron microscopic observations on vascular casts of ciliary processes in normal and topical epinephrine-treated rats.

Existence of neurohumoral control of the ciliary process blood flow was investigated in normal adult Wistar albino rats, utilizing the vascular casting method with a scanning electron microscope, comparing the ciliary process vessels in epinephrine-treated eyes to those in control eyes. The ciliary process microvasculature consisted of marginal capillaries, intraprocess capillaries and collecting veins. The supplying arterioles of the ciliary processes were derived from the iridociliary arterial circle. The arterioles were constricted or annularly impressed just before connecting with the marginal capillaries in the controls. The epinephrine instillation resulted in significant constriction of all the ciliary process vessels. Especially the ciliary process arterioles were narrowed in their full length in contrast to the focal constrictions in the controls. The diameter of the constricted arterioles in the epinephrine-treated eyes was the same as the focal constrictions in the controls. These results suggested that sphincter muscles existed in the wall of the ciliary process arterioles of the rat and that neurohumoral blood flow control was related to the constriction of the ciliary process arterioles resulting from the epinephrine administration.