Giant vacuoles are found preferentially near collector channels.

PURPOSE To determine whether giant vacuoles form preferentially near collector channels or over regions of optically empty space within the juxtacanalicular tissue (JCT). METHODS To assess the relationship between giant vacuoles and collector channels, six eyes were perfused with phosphate-buffered saline (PBS) at 20 mm Hg and then fixed by perfusion. Serial sections were cut in the frontal plane and light microscopy used to count the number of giant vacuoles per length of Schlemm's canal. The number of giant vacuoles between two adjacent collector channels was determined. To assess the relationship between giant vacuoles and the ultrastructure of the JCT, an additional seven eyes were perfused with PBS at 10 mm Hg, fixed by perfusion, and examined by transmission electron microscopy. The ultrastructural components of the JCT were quantitated with an image analysis system. RESULTS Twice as many giant vacuoles were present in regions underlying collector channels as in regions between channels (giant vacuoles per histologic section: 14.0 +/- 1.7 versus 7.3 +/- 0.8, P: = 0.01). Giant vacuoles occurred on both the inner and outer walls of the canal but were more numerous on the inner wall (9.1 +/- 1.0 versus 2.6 +/- 0.4, P: < 0.001). No significant increase in optically empty space was found in the JCT regions underlying giant vacuoles compared with regions with no vacuoles (50.7% +/- 2.3% versus 47.3% +/- 2.5%, P: = 0.09). Examination of the amount of optically empty space immediately adjacent (within 1 microm) to the inner wall endothelial cells of the canal did not reveal a significant difference between regions under vacuoles and regions without giant vacuoles. CONCLUSIONS Giant vacuoles are found preferentially near collector channels, indicating that aqueous flow across the inner wall is sensitive to downstream pressure. The variability in giant vacuole distribution noted in previous studies is in part due to the distance of the vacuoles from the collector channels. No distinct findings in the JCT were associated with the presence of giant vacuoles.