title: Optical quality of the cornea after overnight orthokeratology.
abstract: OBJECTIVE
  To review changes in the optical quality of the cornea induced by overnight orthokeratology for myopia.
  
  
  METHODS
  Sixty-four eyes of 39 patients who underwent overnight orthokeratology for myopia were prospectively examined. Inclusion criteria were uncorrected visual acuity of 20/20 or better after treatment and a minimum follow-up of 3 months. To quantitatively assess changes in corneal regular and irregular astigmatism, videokeratography data were decomposed into spherical component, regular astigmatism, asymmetry, and higher-order irregularity using Fourier analysis. In addition, corneal wavefront aberrations were calculated by expanding anterior corneal height data from videokeratography into a set of orthogonal Zernike polynomials.
  
  
  RESULTS
  Although orthokeratology significantly reduced manifest refraction and improved uncorrected visual acuity, the asymmetry component, which is one of the features of irregular astigmatism, increased significantly from 0.35 +/- 0.22 to 0.64 +/- 0.40 D after treatment (P < 0.0001, paired t test). The increases in the asymmetry component significantly correlated with the amount of myopic correction (Pearson correlation coefficient, R = 0.40, P = 0.0009). Furthermore, the root-mean-square of third-order (coma-like) and fourth-order (spherical-like) aberrations significantly increased after orthokeratology (P < 0.0001, paired t test), and these increases showed significant positive correlations with the amount of myopic correction (Pearson correlation coefficient, R = 0.452, P = 0.0001 and R = 0.381, P = 0.0017, respectively).
  
  
  CONCLUSIONS
  Corneal irregular astigmatism and higher-order aberrations significantly increased even in clinically successful orthokeratology, and the increases correlated with the magnitude of myopic correction. A large myopic correction by orthokeratology should be avoided to not decrease corneal optical quality.
authors.affiliation: Department of Ophthalmology, Institute of Clinical Medicine, University of Tsukuba, 1-1-1 Tennoudai, Tsukuba, Ibaraki 305-8575, Japan. thiraoka@md.tsukuba.ac.jp
authors.forename: Takahiro
authors.initials: T
authors.lastname: Hiraoka
authors.forename: Fumiki
authors.initials: F
authors.lastname: Okamoto
authors.forename: Yuichi
authors.initials: Y
authors.lastname: Kaji
authors.forename: Tetsuro
authors.initials: T
authors.lastname: Oshika
mesh_terms: D000293:Adolescent; D000328:Adult; D001251:Astigmatism / Q000503:physiopathology*; D002648:Child; D003261:Contact Lenses; D003315:Cornea / Q000503:physiopathology*; D019781:Corneal Topography; D005260:Female; D005583:Fourier Analysis; D006801:Humans; D008297:Male; D009216:Myopia / Q000503:physiopathology / Q000628:therapy*; D009988:Orthoptics / Q000379:methods; D011446:Prospective Studies; D014792:Visual Acuity / Q000502:physiology*