Intraocular microendoscopy of the ciliary-process vasculature in albino rabbits: effects of vasoactive agents

The reactions of the ciliary-process microvasculature following administration of various vasoactive substances were studied in the albino rabbit using a new method of intraocular microendoscopy. This technique allows an in vivo observation of arterioles, capillaries and venules of the ciliary body and iris. As long as these tissues are not traumatized, the newly described method of intraocular microendoscopy produces no reactive changes in the vasculature. The video images of microendoscopy were also evaluated quantitatively. Administration of substance P caused a short-term ischemic phase in the ciliary-process vasculature which preceded a long-term hyperaemia. After topical administration of epinephrine as well as intra-arterial administration of epinephrine, phenylephrine and isoproterenol, rapid and intense vasoconstrictory or vasodilatory reactions were seen in the terminal arterioles of the vascular territories in the ciliary processes. The terminal arterioles of the iridial ciliary processes responded faster and more intensely than those of the major ciliary processes. It is concluded that the terminal arterioles play an important role in blood-flow regulation of the ciliary processes and function as special afferent vessel segments which control the circulation within the ciliary-process capillaries.