title: Scanning laser polarimetry retinal nerve fiber layer thickness measurements after LASIK.
abstract: OBJECTIVE
  To compare retinal nerve fiber layer (RNFL) thickness measurements before and after LASIK.
  
  
  METHODS
  Cohort study.
  
  
  METHODS
  Twenty participants undergoing LASIK and 14 normal controls.
  
  
  METHODS
  Retinal nerve fiber layer thickness was measured before LASIK and approximately 3 months after surgery in one eye each of 20 patients using a scanning laser polarimeter (GDx Nerve Fiber Analyzer) with fixed corneal compensation (FCC), one with variable corneal compensation (GDx VCC), and optical coherence tomography (OCT). Fourteen normal controls also were tested at baseline and approximately 3 months later.
  
  
  METHODS
  Retinal nerve fiber layer thicknesses measured with the GDx FCC, GDx VCC, and OCT.
  
  
  RESULTS
  At baseline, mean (95% confidence interval [CI]) RNFL thicknesses for the GDx FCC, GDx VCC, and OCT were 78.1 microm (72.2-83.9), 54.3 microm (52.7-56.0), and 96.8 microm (93.2-100.5), respectively. In both LASIK and control groups, there were no significant changes between baseline and follow-up examinations in GDx VCC and OCT RNFL thickness measurements globally or in the superior and inferior quadrants (mean change, <5 microm for each instrument). In the control group, there also was no significant change in GDx FCC measurements between baseline and follow-up. In LASIK patients, significant reductions were observed in GDx FCC RNFL measurements. Average absolute values of the mean (95% CI) change in thickness were 12.4 microm (7.7-17.2), 15.3 microm (9.6-20.9), and 12.9 microm (7.6-18.1) for GDx FCC RNFL measurements superiorly, inferiorly, and globally, respectively (all Ps < or = 0.001).
  
  
  CONCLUSIONS
  LASIK does not seem to change RNFL thickness. Reduction in GDx FCC RNFL thickness measurements after LASIK is a measurement artifact and is most likely due to erroneous compensation for corneal birefringence. With scanning laser polarimetry, it is mandatory to compensate individually for change in corneal birefringence after LASIK to ensure accurate RNFL assessment.
authors.affiliation: Hamilton Glaucoma Center and the Department of Ophthalmology, University of California, San Diego, California 92093-0946, USA.
authors.forename: Linda M
authors.initials: LM
authors.lastname: Zangwill
authors.forename: Teresa
authors.initials: T
authors.lastname: Abunto
authors.forename: Christopher
authors.initials: C
authors.lastname: Bowd
authors.forename: Raymund
authors.initials: R
authors.lastname: Angeles
authors.forename: David J
authors.initials: DJ
authors.lastname: Schanzlin
authors.forename: Robert N
authors.initials: RN
authors.lastname: Weinreb
mesh_terms: D000328:Adult; D016477:Artifacts; D015331:Cohort Studies; D003319:Corneal Stroma / Q000601:surgery*; D003941:Diagnostic Techniques, Ophthalmological; D005260:Female; D006801:Humans; D007368:Interferometry; D020731:Keratomileusis, Laser In Situ; D007834:Lasers; D008297:Male; D008875:Middle Aged; D009216:Myopia / Q000601:surgery*; D009412:Nerve Fibers / Q000473:pathology*; D009887:Ophthalmoscopy; D011184:Postoperative Period; D011300:Preoperative Care; D012165:Retinal Ganglion Cells / Q000473:pathology*; D041623:Tomography, Optical Coherence