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Faith M McAllister, Laura P Pardon, Ronald S Harwerth, Nimesh Bhikhu Patel; Normal Aqueous Outflow Response To Elevated Intraocular Pressure in the Non-human Primate.. Invest. Ophthalmol. Vis. Sci. 2018;59(9):1652.
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© ARVO (1962-2015); The Authors (2016-present)
Elevated intraocular pressure (IOP) is a risk factor for glaucomatous optic neuropathy. IOP regulation mechanisms, which are essential for maintaining homeostatic IOP levels, are dependent on the rate of aqueous production and outflow. The purpose of this study was to evaluate changes in outflow in response to a mild and moderate pressure increase in healthy non-human primate eyes.
Five healthy rhesus macaque monkeys with no previous experimental intervention were used for this study. A 27G needle was inserted into the anterior chamber of one, randomly selected eye of each animal, which was attached to a closed loop system that included a pressure transducer and syringe pump to maintain a steady IOP. For each eye, at two different sessions, separated by at least 2 weeks, IOP was maintained at either 25mmHg or 40mmHg for 120 minutes and was then changed to 10mmHg for 120 minutes. The total replacement fluid needed to maintain the experimental IOP was calculated in 5 min intervals and used as an estimate of the outflow rate.
The fluid replacement rate increased linearly as a function of time for both the 25mmHg and 40mmHg pressure settings (p<0.01). The rate of change for higher pressures (slope = 0.412±0.338 µl/min/min) was greater than that for the mild IOP increase (slope = 0.108±0.06µl/min/min), (p<0.01). Overall, a greater fluid volume was needed to maintain IOP at 40mmHg (3.31 ± 2.08ml) compared to 25 mmHg (1.23± 0.61ml). Subsequently, when IOP was changed to 10mmHg, the rate of flow as a function of time decreased linearly and was statistically different between when the pressure was initially set at 40mmHg (slope= -0.04x ± 0.022µl/min/min) and 25mmHg (slope= -0.01x ± 0.32µl/min/min) (p<0.01).
Fluid flow rate changes were greater in response to moderate pressure increase (40mmHg) and following recovery of normal pressure compared to the milder pressure increase (25mmHg). These results suggest that the aqueous outflow responds rapidly to changes in IOP in healthy eyes. Controlled pressure experiments can be useful for future studies evaluating variability with age, the effect of pharmaceutical agents on outflow mechanisms, and histological changes of the outflow pathway with elevated pressure.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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