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C. B. Toris, W. W. Dawson, M. A. McLaughlin; Aqueous Humor Dynamics in Rhesus Monkeys With Naturally Occurring Ocular Hypertension. Invest. Ophthalmol. Vis. Sci. 2007;48(13):4894.
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This study evaluates aqueous humor dynamics in Rhesus monkeys with naturally occurring ocular hypertension from the University of Florida inbred colony (Hope, Dawson, Engle, Sherwood et al., Brit. J. Ophthalmol. 1992).
Eight Rhesus monkeys with intraocular pressures (IOPs) less than 18 mmHg in one eye (ONT group) and six Rhesus monkeys with IOPs greater than or equal to 18 mmHg in one eye (OHT group) were included in the study. The OHT eyes were 2 or more standard deviations from the population distribution estimate (Dawson et al., J. Glaucoma, 1998). Assessments included central cornea thickness (CCT, mm) by ultrasound pachymetry, IOP (mmHg) by tonometry, aqueous flow (Fa, µl/min) and outflow facility (Cfl, µl/min/mmHg) by fluorophotometry, and uveoscleral outflow (Fu, µl/min) by mathematical calculation. Animals were sedated with ketamine for all measurements. Values from the two eyes if each animal were averaged. Comparisons between groups were made by Student’s two-tailed unpaired t-tests.
Compared to the normotensive eyes, hypertensive eyes had higher IOPs at all times measured and lower aqueous flow, outflow facility and uveoscleral outflow. Results are summarized in the following table.
The reason for the elevated IOP in inbred Florida Rhesus monkeys is that outflow facility and uveoscleral outflow are significantly reduced. These animals also have lower aqueous flow which alone would reduce rather than increase IOP. The outflow changes are more than sufficient to offset this effect. Interestingly, patients with OHT have similar outflow changes but do not exhibit the reduction in aqueous flow (Toris et al., J Glaucoma, 2002).
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