["To determine whether filtration surgery causes secondary changes in the trabecular meshwork and Schlemm's canal. Successful filtration surgery allows most aqueous outflow to enter the filtration bleb, bypassing the meshwork and canal, and may result in underperfusion of these structures.", "Eyes with primary open-angle glaucoma (POAG) that had undergone filtration surgery were studied and compared with eyes with POAG that had not undergone surgery. In addition, normal eyes and eyes with pseudoexfoliative glaucoma were studied for comparison. The trabecular meshwork and Schlemm's canal were examined by light and electron microscopy.", "Schlemm's canal was significantly smaller in eyes with POAG after filtration surgery than in normal eyes (canal width, 178 +/- 71 microm vs 276 +/- 52 microm; P<.001) or in eyes with medically treated POAG of similar clinical severity (261 +/- 60 microm, P =. 03). The decrease in canal size seemed to be related to the success of the filtration procedure, since eyes with blebs and low pressures had the smallest canals. Eyes with medically treated POAG at earlier clinical stages of glaucoma did not have a significant decrease in canal size when compared with normal eyes. Eyes with advanced pseudoexfoliative glaucoma had canal widths 20% smaller than those in normal eyes (P =.08)."] Does schlemm 's canal become smaller after successful filtration surgery?