Studies of the Retinal Circulation by Direct Microscopy

Abstract

After taking direct photomicrographs of the retinal vessels of animals <i>in vivo</i> and measuring the actual diameter by means of a micrometer scale, then removing the eye and sectioning it along the course of the vessel photographed, it was possible to reconstruct the vessel to its actual living size. The relation of vessel-wall thickness to size of lumen proved to be 1:20. By the same original method for measuring the caliber of the retinal blood vessels of animals, the effect of intravenously injected adrenalin chloride on the size of retinal vessels was investigated. In most experiments there was vasodilatation of the retinal vessels concomitant with the rise in blood pressure; in some of the experiments no change in caliber was seen. The administration of nitroglycerine and amyl nitrite conversely allowed the intraocular pressure to compress the retinal vessels when the force of the blood pressure was diminished and vasoconstriction was found to take place. Attempts to produce a vasomotor reaction by stimulation of the cervical sympathetic were unsuccessful in the cat and monkey; in the rabbit vasoconstriction could be induced. Ligation of the vessels of the carotid arteries in the neck in addition to interfering with the blood supply produced a systemic elevation of the blood pressure, the two effects tending to offset each other. The results of experimentation seemed to indicate that the size of the retinal vessels depends largely upon the inflow of blood to the eye and any vasomotor control is probably more to the retrobulbar vessels than to the retinal vessels themselves. Other factors controlling the size of the retinal vessels are evaluated. From the Research Laboratories, Institute of Ophthalmology, Columbia University. Read before the Association for Research in Ophthalmology, Atlantic City, June 11, 1935.