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Guorong Li, Andrea Wilson, Catherine Bowes Rickman, William Daniel Stamer; Outflow segmentation patterns and pilocarpine induced outflow changes with age. Invest. Ophthalmol. Vis. Sci. 2022;63(7):1288 – F0103.
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© ARVO (1962-2015); The Authors (2016-present)
Age is a critical risk factor for ocular hypertension in glaucoma. But, how age affects the regulation of conventional outflow is unclear. The aim of this study was to determine the effect of age on outflow in the presence or absence of pilocarpine (PILO).
C57BL/6J mice (1-30 month-old) were used for the study. Green fluorescence beads (0.1um) were perfused intracamerally at pressures 15, 20, 25 and 30 mmHg for 10 min at each pressure in live mice. Pressure was set by a column of fluid connected to a cannulation needle, and outflow (OF) was calculated at each pressure level by the volume leaving the column during 10 min intervals. For PILO studies, 1% PILO was applied topically to one eye just before pressure steps. After perfusions, mice were immediately euthanized. Anterior segment flat mounts were imaged by confocal microscopy.
Regardless of age, the inferior quadrant displayed the least amount of tracer in the majority of the eyes. Overall fluorescence intensity decreased in an age dependent manner, with a greater percentage of low flow regions found in eyes of older mice. Eyes treated with PILO showed increased fluorescence intensity in inferior quadrants, especially in aged eyes. However, age did not significantly change averaged OF across all pressures measured in vivo. As expected, PILO significantly increased mean OF in both young and aged eyes (young: 0.36±0.09 vs 0.52±0.14 ul/min, p=0.02, n=7-33; aged: 0.4±0.12 vs. 0.57±0.14 ul/min, p=0.03, n=6-27). Interestingly, PILO effects in young mice was rapid, increasing OF during the first 10 min by 79% at 15 mmHg (0.45±0.17 vs. 0.80±0.37 ul/min, p=0.04) and by 57% during the next 10 min at 20 mmHg (0.34±0.14 vs. 0.53±0.27 ul/min, p=0.11). In contrast, we observed no increase in OF in old mice for the first 20 min of PILO at IOP 15 or 20 mmHg. The last 20 min of PILO perfusion was different in old mice, significantly increasing OF by 67-69% (25 mmHg=0.39±0.15 vs 0.66±0.16 ul/min, p=0.006; 30 mmHg=0.41±0.11 vs. 0.69±0.17 ul/min, p=0.009). By comparison, PILO had no significant effects in young mice over the last 20 min.
Labeled high flow regions were reduced with age, which is consistent with the lower outflow detected in aged human eyes. In addition, age also impacted the effects of PILO on outflow tissues, where young mice showed a rapid response and aged mice had a slower and more constant response.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.
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