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S. Fan, T. V. Johnson, H. Liu, B. M. Ishimoto, C. B. Toris; Aqueous Flow Measured by Fluorophotometry in the Mouse. Invest. Ophthalmol. Vis. Sci. 2007;48(13):3921.
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This study evaluates a noninvasive fluorophotometric method to measure aqueous flow in the mouse.
CD1 mice were divided into three groups, 1) anesthesia with ketamine+xylazine (K/X; 100-200 mg/kg + 5-16 mg/kg, n=24), 2) anesthesia with tribromoethanol (Avertin, 400 mg/kg n=6), 3) Avertin anesthesia plus topical timolol (one 10 µl drop of 0.5% dosed to the left eye one hour prior to anesthesia, n=7). Ninety minutes following topical application of one 10 µl drop of 0.1% fluorescein to the left eye, animals were anesthetized and secured on a heated platform in front of a modified FluorotronTM Master Ocular fluorophotometer. Scans of the left eye were collected at 15 minute intervals for 1.5 to 2 hours. Ten of the mice in Group 1 also were used to measure aqueous flow by a needle method. Following K/X anesthesia, FITC dextran was infused into the anterior chamber at 3µl/min. The volume and dilution of aspirated aqueous humor were used to calculate aqueous flow. Paired T-tests were used to compare measurement methods and unpaired T-tests were used to compare animal groups.
Under K/X anesthesia, aqueous flow by fluorophotometry was 0.09±0.06 ul/min (mean±SD, range: 0.01 - 0.24). The slopes of the cornea and anterior chamber fluorescein decay curves were nearly identical (-0.006 and -0.005, respectively). Aqueous flow in two dead mice was zero. Aqueous flow with Avertin anesthesia was 0.20±0.07 µl/min, which was significantly (p=0.001) greater than with K/X anesthesia. This was significantly (p=0.005) reduced to 0.07±0.02 µl/min with timolol treatment. Aqueous flow in the subset of animals from Group 1 was 0.20±0.13 µl/min (range: 0.06 - 0.44) by the needle method and 0.09±0.07 (range: 0.04 - 0.24) by fluorophotometry. This difference was significant (p=0.05).
A modified Fluorotron fluorophotometer was used to detect changes in fluorescein concentrations over time in the cornea and anterior chamber enabling calculation of aqueous flow in mice. A reduction in aqueous flow by timolol was detectable. The type of anesthesia had a significant effect on aqueous flow. Aqueous flow was lower when measured by fluorophotometry than by the needle method. The needle method showed greater variability, was technically more difficult and was more traumatic to the eye than the fluorophotometry method. As there remains no gold standard for aqueous flow measurement in mice, further study is needed to confirm the accuracy of the fluorophotometry method. The modified Fluorotron shows potential for the study of aqueous flow by noninvasive means in the mouse.
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