Giant vacuoles are found preferentially near collector channels

PURPOSE. To determine whether giant vacuoles form preferentially near colle ctor channels or over regions of optically empty space within the juxtacana licular tissue (JCT). METHODS. To assess the relationship between giant vacuoles and collector ch annels, six eyes were perfused with phosphate-buffered saline (PBS) at 20 m m Hg and then fixed by perfusion. Serial sections were cut in the frontal p lane and light microscopy used to count the number of giant vacuoles per le ngth 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 transmis sion electron microscopy. The ultrastructural components of the JCT were qu antitated with an image analysis system. RESULTS. Twice as many giant vacuoles were present in regions underlying co llector channels as in regions between channels (giant vacuoles per histolo gic section: 14.0 +/- 1.7 versus 7.3 +/- 0.8, P = 0.01). Giant vacuoles occ urred 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 signific ant increase in optically empty space was found in the JCT regions underlyi ng giant vacuoles compared with regions with no vacuoles (50.7% +/- 2.3% ve rsus 47.3% +/- 2.5%, P = 0.09). Examination of the amount of optically empt y space immediately adjacent (within 1 mu m) 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 channel s, indicating that aqueous flow across the inner wall is sensitive to downs tream pressure. The variability in giant vacuole distribution noted in prev ious studies is in part due to the distance of the vacuoles from the collec tor channels. No distinct findings in the JCT were associated with the pres ence of giant vacuoles.