Ciliary Oxygen Tension, Ciliary Blood Flow and Brimonidine

Abstract

Abstract: : Purpose: To measure oxygen tension (PO₂) and blood flow (CBF)in the ciliary body simultaneously and to investigate the effectof brimonidine on these two parameters. Methods: All experimentswere performed in anesthetized new Zealand white rabbits (n=7).For measurements of oxygen tension, oxygen sensitive microelectrodeswere advanced through a scleral window and placed in the vicinityof the ciliary body. CBF was measured by laser Doppler flowmetry,intraocular pressure (IOP) was measured via direct cannulationof the vitreous and mean arterial pressure (MAP) was measuredthrough a catheter in the ear artery. Brimonidine was appliedtopically on the cornea (40 µl, 0.15 %) Results: 

Brimonidine lowered IOP, CBF andPO₂ significantly, however, no significant effect on MAP wasobserved. Conclusions: It is possible to measure ciliary PO₂and ciliary blood flow simultaneously in this rabbit model.Despite the increase in perfusion pressure (MAP-IOP), CBF wasdecreased by brimonidine which indicates it is a potent vasoconstrictorin the ciliary circulation. In addition, it reduces PO₂ measuredin the vicinity of the ciliary processes. Baseline changes  

Keywords: ciliary body • blood supply • hypoxia