title: Noncontact optical coherence tomography for measurement of corneal flap and residual stromal bed thickness after laser in situ keratomileusis.
abstract: OBJECTIVE
  Studies show significant variability in the thickness of laser in situ keratomileusis (LASIK) corneal flaps cut by various microkeratomes. Most studies of corneal flap thickness are based on contact ultrasonic pachymetry measurements taken during the surgical procedure. This study reports a technique to obtain reproducible corneal flap thickness and residual stromal bed thickness measurements using noncontact optical coherence tomography (OCT) following LASIK.
  
  
  METHODS
  The corneal flap thicknesses of 26 eyes of 15 patients were measured following LASIK in which the flap was created using the Amadeus microkeratome: 160-microm head, 9.5-mm ring, 4.0-mm/s translation speed, 8000 oscillations/m, and full vacuum. Zeiss Humphrey OCT-2 line scans were performed on postoperative days 1 and 7. The raw data from three scans for each eye and day were exported to Microsoft Excel for processing, averaging, and analysis.
  
  
  RESULTS
  The OCT corneal flap thickness and residual stromal bed thickness measurements correlated well with ultrasonic pachymetry measurements performed during surgery (R2 = .92). The OCT technique yielded reproducible results, as the variance for repeated scans was only 2.5% of the variance between eyes. In bilateral cases a single blade was used for both eyes. The mean flap thickness of 15 first eyes was significantly greater than that of the 10 second eyes: 181 +/- 31 microm vs. 143 +/- 41 microm (P < .01). A positive correlation was found between the preoperative pachymetry and corneal flap thickness.
  
  
  CONCLUSIONS
  The OCT scan averaging technique is a reproducible, noncontact postoperative method for measuring corneal flap and residual stromal bed thicknesses following LASIK.
mesh_terms: D000328:Adult; D003319:Corneal Stroma / Q000473:pathology* / Q000601:surgery; D005260:Female; D006801:Humans; D020731:Keratomileusis, Laser In Situ; D008297:Male; D008875:Middle Aged; D011184:Postoperative Period; D054140:Refractive Surgical Procedures; D013524:Surgical Flaps / Q000473:pathology*; D041623:Tomography, Optical Coherence; D016896:Treatment Outcome; D014792:Visual Acuity