The peripheral vascular system in the bulbar conjunctiva of young normotensive adults at rest

The recent development of specialized direct techniques for observation and measurement has added greatly to knowledge concerning the anat-omy and function of the capillary bed in several species of small mammals (1-5). The spatial ar-rangement of vascular elements, vessel sizes, and relative velocities of blood flow have been estab-lished. In addition, the nature of spontaneous vasomotor activity, the relative sensitivity to vaso-constrictor agents, and other criteria, have been found suitable for the determination and compari-son of peripheral vascular function in certain differ-ent experimental conditions (6-8). There has been little direct information obtained, however, regarding the reactivity and patterns of response to stimuli in the capillary blood vessels of man. This has resulted primarily from a lack of suitable techniques and the inaccessability of readily visu-alized complete peripheral vascular networks in the unanesthetized human. The present study is an attempt to apply some of the methods found useful in the experimental animal to observation and evaluation of the human capillary bed. With suitable apparatus, it was noted that the terminal vessels in the bulbar conjunctiva could be observed without difficulty and photographed at relatively high magnification. In addition, their exposed position allowed measurement of peripheral vas-cular reactions to a vasoconstrictor agent (epi-nephrine) applied directly to the area studied in known concentration. This procedure, based upon a knowledge of the anatomy in the capillary bed, permitted a comparison of the relative sensitivity of arterioles, precapillaries, and venules to a vaso-constrictor stimulus. 1 This study was supported by grants from the Ameri