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Relationship between Ciliary Blood Flow and Aqueous Production in Rabbits

¹From the Departments of Physiology and ²Clinical Pharmacology, University of Vienna Medical School, Vienna, Austria; and the ³Department of Ophthalmology, University of Texas Health Science Center, San Antonio, Texas.

PURPOSE. To determine the relationship between ciliary blood flow and aqueous flow by changing the mean arterial pressure (MAP) mechanically under controlled conditions in an animal model.

METHODS. In anesthetized rabbits, MAP and intraocular pressure (IOP) were measured by direct cannulation. MAP was controlled with occluders placed on the aorta and vena cava. In group 1 (n = 22), aqueous flow was measured by fluorophotometry. In group 2 (n = 21), ciliary blood flow was measured by laser Doppler flowmetry. In separate subgroups, measurements were made for 60 minutes at the control MAP of 70 mm Hg and for an additional 60 minutes at target MAPs of 80, 55, or 40 mm Hg.

RESULTS. The target MAPs achieved perfusion pressures (MAP - IOP) of 33.6 ± 1.0, 43.5 ± 0.7, 51.9 ± 0.6, and 65.2 ± 0.9 mm Hg. Ciliary blood flow was unaffected by increased perfusion pressure, but decreased progressively as perfusion pressure was lowered. Aqueous flow decreased only at the lowest perfusion pressure.

CONCLUSIONS. Under control conditions in anesthetized rabbits, aqueous production is independent of ciliary blood flow until ciliary blood flow declines below 74% of control. At ciliary blood flow below this critical level, aqueous production is blood flow dependent.

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