title: Changes in corneal biomechanics and intraocular pressure following LASIK using static, dynamic, and noncontact tonometry.
abstract: OBJECTIVE
  To compare the preoperative and postoperative measurement of corneal biomechanical properties and intraocular pressure (IOP) using Goldmann applanation tonometry (GAT), the ocular response analyzer (ORA), and the Pascal dynamic contour tonometer (PDCT) in eyes undergoing myopic laser in situ keratomileusis (LASIK).
  
  
  METHODS
  Prospective, nonrandomized clinical trial.
  
  
  METHODS
  IOP was measured in 66 myopic eyes before and after LASIK by GAT, ORA, and PDCT in a randomized sequence. Metrics of corneal biomechanical properties (corneal hysteresis [CH], corneal resistance factor [CRF], and ocular pulse amplitude [OPA]) were recorded.
  
  
  RESULTS
  After LASIK, there was a reduction in mean corneal pachymetry of 90.2 mum and in IOP measurements with GAT (Delta = -1.8 +/- 2.8 mm Hg; P < .01), ORA-Goldmann (Delta = -4.6 +/- 2.8 mm Hg, P < .01), and ORA-corneal compensated (Delta - 2.1 +/- 2.6 mm Hg; P < .05). However, there was no statistically significant difference between preoperative and postoperative IOP measurements taken by PDCT (Delta = -0.5 +/- 2.6 mm Hg). Postoperatively, CRF decreased by 28.6% (P < .01), CH by 16.2% (P < .01), and OPA by 1.8% (P = .32).
  
  
  CONCLUSIONS
  Measurement of IOP with PDCT appears to be relatively immune to changes in corneal biomechanics and pachymetry after LASIK, in comparison to GAT and ORA measures of IOP. PDCT and ORA both showed statistically lower variation in measurement than GAT. LASIK produced a marked decline in CH and CRF, which may reflect respective changes in the viscous and elastic qualities of the post-LASIK cornea. In contrast, there was no statistical change in OPA.
authors.affiliation: Pepose Vision Institute, 16216 Baxter Road, Chesterfield, MO 63017, USA. jpepose@peposevision.com
authors.forename: Jay S
authors.initials: JS
authors.lastname: Pepose
authors.forename: Susan K
authors.initials: SK
authors.lastname: Feigenbaum
authors.forename: Mujtaba A
authors.initials: MA
authors.lastname: Qazi
authors.forename: Jeffrey P
authors.initials: JP
authors.lastname: Sanderson
authors.forename: Cynthia J
authors.initials: CJ
authors.lastname: Roberts
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D003315:Cornea / Q000000981:diagnostic imaging / Q000502:physiology* / Q000601:surgery; D019781:Corneal Topography; D005260:Female; D006801:Humans; D007429:Intraocular Pressure / Q000502:physiology*; D020731:Keratomileusis, Laser In Situ; D008297:Male; D009216:Myopia / Q000503:physiopathology / Q000601:surgery*; D011446:Prospective Studies; D014065:Tonometry, Ocular / Q000379:methods*; D014463:Ultrasonography