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H Gong, Q Qiu, P Wu, D Overby, TF Freddo; Reconsideration Of Schlemm's Canal As A Vessel Sui Generis . Invest. Ophthalmol. Vis. Sci. 2002;43(13):1029.
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Purpose: The simultaneous presence of a continuous endothelium but a discontinuous basement membrane (BM) in Schelmm's canal (SC) has prompted its categorization as a vessel sui generis. The purpose of this study was an explore the alternate possibility that the discontinuities in the BM along the inner wall of Schlemm's are the result of aqueous flow rather than a programmed feature of inner wall cells. To address this question we determine if changes in the continuity of the BM along the inner wall of Schlemm's canal occur in normal eyes with changes in perfusion pressure. Methods: Ten normal human eyes were either perfusion-fixed (at 15 or 45 mmHg) or immersion-fixed (0mmHg) following recording of facility. The basement membrane component type IV collagen, was labeled with monoclonal antibody and examined using confocal microscopy. The basement membrane components heparan sulfate was stained using cuprolinic blue in a 'critical electrolyte concentration' with or without pre-digestion with heparitinase and examined using electron microscopy. Morphometric analysis was conducted in both confocal images and electron micrographs. Results: In both immersion and perfusion-fixed eyes, a discontinuous BM was found along the inner wall of SC. More breaks were found in perfusion-fixed eyes compared to immersion-fixed eyes (p< 0.05). A trend was observed suggesting that more breaks in BM continuity occur with increasing pressure, but significant differences were not reached. Discontinuities in the BM were present more often in areas containing high concentrations of vacuoles and especially where openings into giant vacuoles were present. Areas surrounding distended vacuoles were more likely to exhibit discontinuities than were areas in which vacuoles had a flattened morphology. Conclusion: This data suggests that the discontinuities in the BM along the inner wall of SC may be the secondary consequence of vacuole formation and outflow rather than the unique expression of a vessel sui generis as has been previously suggested.
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