title: Schlemm's canal becomes smaller after successful filtration surgery.
abstract: OBJECTIVE
  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.
  
  
  METHODS
  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.
  
  
  RESULTS
  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).
  
  
  CONCLUSIONS
  Filtration surgery was associated with a decrease in the size of Schlemm's canal, most likely due to underperfusion of the meshwork. A significant decrease in canal size is otherwise not a finding in POAG. In contrast, the canal tended to become smaller in advanced cases of pseudoexfoliative glaucoma.
  
  
  CONCLUSIONS
  The decrease in size of Schlemm's canal after successful filtration surgery could make glaucoma more difficult to control if the filter ultimately fails. Arch Ophthalmol. 2000;118:1251-1256
authors.affiliation: Department of Opthamology, Mayo Clinic, 200 First Street SW, Rochester, MN 55905, USA. johnson.douglas@mayo.edu
authors.forename: D H
authors.initials: DH
authors.lastname: Johnson
authors.forename: Y
authors.initials: Y
authors.lastname: Matsumoto
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D017889:Exfoliation Syndrome / Q000473:pathology / Q000601:surgery*; D018463:Filtering Surgery / Q000009:adverse effects*; D005902:Glaucoma, Open-Angle / Q000473:pathology / Q000601:surgery*; D006801:Humans; D011183:Postoperative Complications / Q000473:pathology*; D012590:Sclera / Q000473:pathology*; D014129:Trabecular Meshwork / Q000473:pathology*