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M. A. Maslonka, S. Fan, L. S. Stapp, C. B. Toris; The Effects of Age on Aqueous Humor Dynamics and Intraocular Pressure in a Monkey Model of Glaucoma. Invest. Ophthalmol. Vis. Sci. 2010;51(13):158.
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The purpose of this longitudinal study was to compare aqueous humor dynamics and intraocular pressure (IOP) during and after puberty in monkeys with unilateral laser-induced glaucoma.
Fourteen female cynomolgus monkeys had laser treatments to the trabecular meshwork of the left eye to induce a stable and chronic elevation in IOP. Lasering had been done at least 13 months before the first day of measurements. In ketamine-sedated animals, seated IOPs were measured by pneumatonometry at three different times throughout the day. Aqueous flow (Fa) was assessed by fluorophotometry, and outflow facility was evaluated by fluorophotometry (Cfl) and by 2-minute tonography (Cton). Uveoscleral outflow was mathematically calculated using either Cfl or Cton in the Goldmann equation to yield Fufl or Futon, respectively. Measurements taken on Study Day I (3.8±0.8 years old) was repeated nearly 3 years later on Study Day II (6.6±2.0 years old). Comparisons between ages and between eyes were made by two-tailed paired t-tests (p).
Comparing the normal eye on Study Day II with Study Day I, the mean IOP (at noon) decreased by 5.5 mmHg (p=0.001), Cfl increased by 0.13 µl/min/mmHg (p=0.07) and Fu increased 1 to 1.5-fold (p=0.03 for Futon and p=0.07 for Fufl). Similar comparisons in the lasered eye found no change in IOP but an increase in Cton (p=0.03). Comparing the lasered eye with the normal eye on Study Day I showed a decrease in mean Cton of 0.20 µl/min/mmHg (p= 0.02). On Study Day II, compared to the normal eye, the lasered eye had an IOP at noon that was higher by 8.3 mmHg (p=0.003), lower mean Cfl by 0.18 µl/min/mmHg (p=0.0001) and higher mean Futon by 1.5 fold (p=0.02). All other comparisons showed no significant differences.
As the young monkey matured, the IOP in the normotensive eye decreased because outflow facility and uveoscleral outflow increased. In the contralateral lasered eye, the IOP increased over time because outflow facility decreased. Concurrently, the lasered eye had an increase in the uveoscleral outflow. Apparently, the fluid was redirected into the healthy uveoscleral outflow pathway from the laser damaged trabecular outflow pathway.
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