title: Corneal Biomechanical Changes After Trabeculectomy and the Impact on Intraocular Pressure Measurement.
abstract: OBJECTIVE
  To evaluate corneal biomechanical changes induced by trabeculectomy and their impact on intraocular pressure (IOP) measurements.
  
  
  METHODS
  In total, 35 eyes of 35 consecutive glaucoma patients undergoing first-time trabeculectomy with mitomycin C were enrolled in this prospective interventional case series. Goldmann applanation tonometry (GAT) IOP, central corneal thickness, axial length, and Ocular Response Analyzer measurements [Goldmann-correlated IOP (IOPg), corneal-compensated IOP (IOPcc), corneal hysteresis (CH), and corneal resistance factor (CRF)] were assessed before and 6 months after uncomplicated trabeculectomy. Linear mixed models were used to compare the parameters before and after surgery.
  
  
  RESULTS
  IOP, central corneal thickness, and axial length showed a strong correlation with CH and CRF preoperatively and postoperatively. After adjusting for these influencing factors, CH changed from 7.75±1.46 to 7.62±1.66 mm Hg (P=0.720) and CRF from 8.67±1.18 to 8.52±1.35 mm Hg (P=0.640) after trabeculectomy, but these changes were not statistically significant. IOP decreased statistically significantly with all IOP measurements (P=0.001). IOPcc was statistically significantly higher than GAT (4.82±5.24 mm Hg; P=0.001) and IOPg (2.92±1.74 mm Hg; P=0.001) preoperatively and postoperatively (GAT, 3.29±3.36 mm Hg; P=0.001; IOPg, 3.35±1.81 mm Hg; P=0.001). The difference between IOPcc and GAT (P=0.5) and IOPcc and IOPg (P=0.06) did not change significantly before or after trabeculectomy.
  
  
  CONCLUSIONS
  Despite a marked IOP reduction and a possible weakening of the ocular walls after trabeculectomy, corneal structural tissue properties are not altered, and therefore, the accuracy of IOP measurements is not changed postoperatively. It seems likely, however, that Goldmann-correlated IOP measurements are underestimated in glaucoma patients before and after surgery.
authors.affiliation: Department of Ophthalmology, Medical Faculty Carl Gustav Carus, University of Technology, Dresden, Germany.
authors.forename: Karin R
authors.initials: KR
authors.lastname: Pillunat
authors.forename: Eberhard
authors.initials: E
authors.lastname: Spoerl
authors.forename: Naim
authors.initials: N
authors.lastname: Terai
authors.forename: Lutz E
authors.initials: LE
authors.lastname: Pillunat
mesh_terms: D000328:Adult; D000368:Aged; D058452:Axial Length, Eye; D001696:Biomechanical Phenomena; D003315:Cornea / Q000033:anatomy & histology / Q000502:physiology*; D005260:Female; D005901:Glaucoma / Q000503:physiopathology / Q000601:surgery*; D006801:Humans; D007429:Intraocular Pressure / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D011184:Postoperative Period; D011446:Prospective Studies; D014065:Tonometry, Ocular / Q000592:standards; D014130:Trabeculectomy