title: Comparison of two partial coherence interferometers for corneal pachymetry in high myopia and after LASIK.
abstract: OBJECTIVE
  We aimed to compare the Haag-Streit optical low-coherence reflectometry (OLCR) pachymeter and the Zeiss Anterior Chamber Master (ACMaster) for measuring central corneal thickness (CCT) in high myopes and after laser in situ keratomileusis (LASIK) for myopia.
  
  
  METHODS
  Central corneal thickness was measured in 55 eyes of 30 myopic subjects (spherical equivalent refraction of - 5.25 D to - 10.75 D, maximal astigmatism of - 2 D), and in 37 eyes of 21 patients 3 months after LASIK for myopia (preoperative spherical equivalent refraction of - 6.0 D to - 10.75 D, maximal astigmatism of - 2 D). All measurements were performed with the Haag-Streit OLCR pachymeter and the Zeiss ACMaster, using group refractive indices of 1.376 and 1.3851, respectively. Thickness measurements were compared using paired t-tests, Pearson's correlation, linear regression and Bland-Altman plots.
  
  
  RESULTS
  In myopic subjects, CCT measured 531 +/- 28 microm and 533 +/- 27 microm with the OLCR pachymeter and the ACMaster, respectively (p < 0.01); all measurements correlated closely (r = 0.99, p < 0.01). In LASIK-treated eyes, CCT measured 472 +/- 24 microm using the OLCR pachymeter and 475 +/- 23 microm using the ACMaster (p < 0.01), again with close correlation between the two instruments (r = 0.99, p < 0.01).
  
  
  CONCLUSIONS
  Measurements of CCT in high myopes and after myopic LASIK were very similar with the Haag-Streit OLCR pachymeter and the Zeiss ACMaster. Using the current group refractive indices, the observed difference between the two instruments of < 3 microm is of little clinical importance. Thus, it would seem safe to use the OLCR pachymeter and the ACMaster interchangeably for CCT measurements in myopia as well as after myopic LASIK.
authors.affiliation: Department of Ophthalmology, Arhus University Hospital, Nørrebrogade 44, Arhus, Denmark. ai@dadlnet.dk
authors.forename: Anders
authors.initials: A
authors.lastname: Ivarsen
authors.forename: Niels
authors.initials: N
authors.lastname: Ehlers
authors.forename: Jesper
authors.initials: J
authors.lastname: Hjortdal
mesh_terms: D003315:Cornea / Q000473:pathology*; D006801:Humans; D007368:Interferometry / Q000295:instrumentation* / Q000379:methods*; D020731:Keratomileusis, Laser In Situ; D047728:Myopia, Degenerative / Q000473:pathology* / Q000601:surgery*; D011184:Postoperative Period; D011300:Preoperative Care