In Vivo Quantification of Anterior and Posterior Chamber Volumes in Mice: Implications for Aqueous Humor Dynamics

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Purpose: Aqueous humor inflow rate, a key parameter influencing aqueous humor dynamics, is typically measured by fluorophotometry. Analyzing fluorophotometric data depends, inter alia, on the volume of aqueous humor in the anterior chamber but not the posterior chamber. Previous fluorophotometric studies of the aqueous inflow rate in mice have assumed the ratio of anterior:posterior volumes in mice to be similar to those in humans. Our goal was to measure anterior and posterior chamber volumes in mice to facilitate better estimates of aqueous inflow rates. Methods: We used standard near-infrared (NIR) optical coherence tomography (OCT) and robotic visible-light OCT (vis-OCT) to visualize, reconstruct, and quantify the volumes of the anterior and posterior chambers of the mouse eye in vivo. We used histology and micro-computed tomography (CT) scans to validate relevant landmarks from ex vivo tissues and facilitate in vivo measurement. Results: Posterior chamber volume is 1.1 times the anterior chamber volume in BALB/cAnNCrl mice, that is, the anterior chamber constitutes about 47% of the total aqueous humor volume, which is very dissimilar to the situation in humans. Anterior chamber volumes in 2-month-old BALB/cAnNCrl and C57BL6/J mice were 1.55 ± 0.36 µL (n = 10) and 2.05 ± 0.25 µL (n = 10), respectively. This implies that previous studies likely overestimated the aqueous inflow rate by approximately twofold. Conclusions: It is necessary to reassess previously reported estimates of aqueous inflow rates and, thus, aqueous humor dynamics in the mouse. For example, we now estimate that only 0% to 15% of aqueous humor drains via the pressure-independent (unconventional) route, similar to that seen in humans and monkeys.

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