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A.L. Evans, C.R. Ethier, A.T. Read, M. Johnson; Distribution of the Pores in the Inner Wall of Schlemm’s Canal . Invest. Ophthalmol. Vis. Sci. 2004;45(13):5024.
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Purpose: Vascular endothelial cells are known to respond in a variety of ways to mechanical stress, particularly to shear stress induced on their apical surfaces by fluid flow. To determine if pore formation in the inner wall of Schlemm’s canal is influenced by shear stresses due to circumferential flow of aqueous humor in Schlemm's canal, the distribution of inner wall pores was measured as a function of distance from collector channel openings, where the aqueous humor flow rate and shear stress are presumed to be greatest. Methods: Two ostensibly normal human eyes were fixed at 8 mmHg and 30 mmHg, respectively, and Schlemm’s canal was microdissected open, allowing inner and outer walls to be simultaneously visualized and aligned with each other. Pores were identified from scanning electron micrographic montages, and the density of pores as a function of distance from the collector channels was measured. A weighted linear regression was used to analyze the data, accounting for the variation in inner wall area as a function of distance from collector channel ostia. Results: In 5 of 6 montages analyzed, the pore distribution was not random (p<0.01). In these five montages, there was a negative correlation between pore density and distance from the collector channel ostium, indicating that pores were more densely distributed near the collector channel. There were no significant differences between montages from eyes fixed at 8 mmHg and 30 mmHg, although the p–values for the montages from the eye fixed at 30 mmHg tended to be lower. The cells of the inner wall were also noted to align with the direction of flow towards the collector channel as seen in other studies. Conclusion: The distribution of pores in the inner wall of Schlemm’s canal is denser where the flow of aqueous humor is greatest, supporting the hypothesis that the pores are influenced by circumferential flow in Schlemm’s canal. These results emphasize the spatially non–uniform nature of aqueous humor drainage through the outflow system. Support: Canadian Institutes of Health Research 10051 (CRE) and R01EY09699.
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