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Wenjie Zhan, Brian C Samuels; Fluorophotometric Study of Aqueous Humor Dynamics in Normal Rats and Rats Treated with a Topical Glaucoma Medication.. Invest. Ophthalmol. Vis. Sci. 2016;57(12):6448.
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© ARVO (1962-2015); The Authors (2016-present)
Intraocular pressure (IOP) is determined by a balance between the rate of aqueous production, facility of outflow, and episcleral venous pressure. Aqueous production and the flow of aqueous can be determined using fluorophotometry. This method, introduced by Jones and Maurice in 1966, has been primarily used for research in humans, primates and rabbits. However, there is still interest in using rodents for aqueous humor studies due to their low cost and easy husbandry. The purpose of this study was to use the Fluorotron Master Laboratory Animal Edition (Ocumetrics, Inc., Mountain View, CA, USA) to measure the aqueous dynamics in rats for the first time.
Under isoflurane anesthesia (3% at O2 flow of 1.5L/min) one drop of a 0.25% fluorescein sodium/0.4% benoxinate hydrochloride opthalmic solution was instilled onto the eye Q10 mins x 4 in male Sprague-Dawley rats (n=4, wt 225-249g). After 2 hours, the rats were placed in a darkened room with the study eye aligned with fluorophotometer. Three consecutive scans along the visual axis were taken every 10 minutes for 2 hours to measure fluorescein concentration in the anterior chamber. In a separate set of experiments, fluorophotometry was completed before and after one drop of 0.2% brimonidine tartate/0.5% timolol maleate was instilled into the eye.
Under baseline conditions, the slope of the fluorescein concentration change in the anterior chamber was -.0052±0.0015 ng/ml.min. This corresponds to an aqueous flow in rats of 0.466±0.13 ul/min with the aqueous humor being turned over every 34.34±10.22 min. As expected, topical application of brimonidine/timolol combination drops significantly changed aqueous flow. The slope of fluorescein concentration change in anterior chamber was reduced from -0.0064±0.0004 ng/ml.min pre-treatment to -0.0039±0.0013 ng/ml.min post-treatment (P<0.05). Aqueous flow changed from 0.676±0.2 µl/min to 0.1865±0.06 µl/min (p<0.05) and significantly increased the time for total aqueous turnover from 23.39± 5.41 min to 89.55± 8.58 min (P<0.05).
The Fluorotron Master Lab Animal Edition can be used to accurately measure the aqueous humor flow in rats under baseline conditions and after use of pharmacologic agents that alter aqueous humor dynamics.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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