Outflow physiology of the mouse eye: Pressure dependence and washout

PURPOSE. Mice are commonly used in glaucoma research, but relatively little is known about aqueous outflow dynamics in the species. To facilitate future use of the mouse as a model of aqueous humor outflow, several fundamental physiological parameters were measured in the mouse eye. METHODS. Eyes from adult mice of either sex (C57BL/6 background) were enucleated, cannulated with a 33-gauge needle, and perfused at constant pressure while inflow was continuously measured. RESULTS. At 8 mm Hg, total outflow facility (C_total) was 0.022 ± 0.005 μL/min/mm Hg (all values mean ± SD; n =21). The flow-pressure relationship was linear up to 35 mm Hg. The conventional outflow facility (C_conv) was 0.0066 ± 0.0009 μL/min/mm Hg, and the unconventional outflow (Fu) was 0.114 ± 0.019 μL/min, both measured at room temperature. At 8 mm Hg, 66% of the outflow was via the unconventional pathway. In a more than 2-hour-long perfusion at 8 mm Hg, the rate of facility change was 2.4% ± 5.4% (n = 11) of starting facility per hour. The ocular compliance (0.086 ± 0.017 μL/mm Hg; n = 5) was comparable to the compliance of the perfusion system (0.100 ± 0.004 μL/mm Hg). CONCLUSIONS. Mouse eyes are similar to human eyes, in that they have no detectable washout rate and a linear pressure-flow relationship over a broad range of intraocular pressures. Because of the absence of washout and the apparent presence of a true Schlemm's canal, the mouse is a useful model for studying the physiology of the inner wall of Schlemm's canal and the conventional outflow tissues.