An in vitro method with perfusion of the posterior segment of the enucleated cat eye allows evaluation of the direct effects of drugs on the blood flow rate through the optic nerve, retina, and choroid. The presence of α-receptors in the posterior segment is suggested by the vasoconstriction produced by levarterenol (norepinephrine), a predominantly α-stimulator, and inhibition of this response by tolazoline (Priscoline), an α-blocker. Isoxsuprine hydrochloride and nylidrin produce dilatation of the posterior segment blood vessels probably by a mechanism other than β-stimulation. The cholinergic drug pilocarpine induces a vasodilatation, whereas physostigmine (eserine) is a vasoconstrictor. Ergotamine tartrate and ouabain are both vasoconstricting agents. The activity of all these agents is primarily on the short ciliary arteries in the area where they pierce the sclera.
Morgan WE, Macri FJ. Vascular Responses of the Posterior Segment of the Cat Eye. Arch Ophthalmol. 1968;79(6):779-784. doi:10.1001/archopht.1968.03850040781023