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P.A. Scott, S.A. Kasper, D.R. Overby, T.F. Freddo, H. Gong; Relationship Between Outflow Facility and the Pattern of Aqueous Humor Drainage in the Bovine Eye . Invest. Ophthalmol. Vis. Sci. 2005;46(13):1350.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To determine whether changes in outflow facility (C) correlate with aqueous outflow patterns in the trabecular meshwork/juxtacanalicular connective tissue (TM/JCT) during washout in enucleated bovine eyes. Methods: 14 bovine eyes were perfused at 15 mmHg with Dulbecco’s PBS, containing 5.5 mM glucose (DPBS), while C was continuously measured. Two colors of fluorescent microspheres (0.5 mm; 0.002% v/v) were used to probe for changes in outflow patterns before and after washout, and after washout reversal. Short–duration perfusion: (n=5), 0.5 mL DPBS containing pre–washout red tracer (RT), followed by anterior chamber exchange with Karnovsky's fixative and perfusion–fixation at 15 mmHg. Long–duration perfusion: (n=5), 0.5 mL DPBS containing pre–washout tracer, then 5 mL of DPBS without tracer to induce washout, followed by 0.5 mL of DPBS containing post–washout green tracer (GT) and perfusion–fixation. Long–duration perfusion plus washout reversal: (n=4), 5 mL of DPBS without tracer to induce washout, then 0.5 mL DPBS containing post–washout GT, followed by a 1 hour reduction to 0 mmHg to reverse washout. The eyes were then perfused with 0.5 mL of DPBS containing post–reversal RT and were perfusion–fixed. Sections (150 mm) were cut both in the radial and tangential direction to the limbus in all quadrants, nuclei were stained with To–Pro 3, and sections examined using confocal laser microscopy to visualize the tracer distribution within the TM/JCT. Results: The distribution of the pre–washout RT was similar in all eyes, exhibiting a punctate pattern within the TM/JCT that tended to cluster near collector channel ostia. After long–duration perfusion and washout in 9 eyes, C increased by 159±25% (mean±SEM) (p<0.0003). The post–washout GT was found in the same areas as the pre–washout RT, however the post–washout tracer was more concentrated and was present in an expanded area surrounding the pre–washout tracer distribution. After dropping the pressure to 0 mmHg for 1 hour to reverse the washout effect, C decreased by 21±6% (p=0.02) and the post–reversal tracer pattern reverted to a more punctate pattern, approximating the pre–washout condition. Conclusions: The macroscopic pattern of aqueous humor outflow is highly segmental at 15 mmHg. Outflow facility appears to correlate in a reversible manner with the area available for flow through the TM/JCT. A better understanding of the mechanisms that augment the total area for flow could be exploited to increase facility in eyes with elevated IOP.
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