The relationship between aqueous humor flow and anterior chamber protein concentration in rabbits

Protein concentration in the anterior chamber of noninflamed eyes is determined by three factors: the rate of protein entry into the aqueous humor (AH), the removal rate by bulk flow of AH, and the anterior chamber volume. On the basis of observations by previous investigators and the authors' computational modeling, it was hypothesized that a direct reciprocal relationship exists between aqueous flare and AH flow. This relationship was studied in pigmented rabbits, under several conditions, to determine the validity of the hypothesis that changes in aqueous flare intensity reflect variations in AH flow rate.

Aqueous flare and AH flow were measured in rabbits entrained to a 12 hr light: 12 hr dark cycle, starting at 6 AM, which subsequently was phase-shifted 6 hr earlier to allow measurements over the light-to-dark transition period. AH flow rates were determined fluorophotometrically using the clearance method after corneal deposition of fluorescein. A Kowa FC1000 cell/flare meter was used to measure aqueous flare. Predictions of anterior chamber protein concentration were made using a computer model of plasma-derived protein diffusion into AH. The response to changes primarily of AH flow were evaluated by concurrently determining flare and flow before and after administration of intravenous acetazolamide.

Aqueous flare decreased 40% during constant light and 47% over the light-dark transition in a parallel, monophasic manner. AH flow did not change significantly under either condition. In contrast, acetazolamide-induced changes in AH flow resulted in reciprocal changes in flare that could be simulated with the computer model through flow parameter changes alone.

Anterior chamber protein concentration in rabbits appears to be modulated both by factors affecting AH flow and protein entry into the aqueous. Thus, in rabbits, changes in aqueous flare do not necessarily reflect AH flow changes.