title: Quantitative evaluation of regular and irregular corneal astigmatism in patients having overnight orthokeratology.
abstract: OBJECTIVE
  To quantitatively assess changes in regular and irregular corneal astigmatism in patients having overnight orthokeratology.
  
  
  METHODS
  Matsumoto Eye Clinic, Ibaraki, Japan.
  
  
  METHODS
  A prospective study was conducted of 64 eyes of 39 patients having overnight orthokeratology for myopia. Inclusion criteria were an uncorrected visual acuity (UCVA) of 20/20 or better after treatment and a minimum follow-up of 3 months. Using Fourier series harmonic analysis, videokeratography data were decomposed into spherical component, regular astigmatism, asymmetry (tilt or decentration), and higher-order irregularity.
  
  
  RESULTS
  Orthokeratology significantly reduced the manifest refraction from -2.60 diopters (D) +/- 1.13 (SD) to -0.17 +/- 0.31 D (P<.0001, paired t test) and improved the UCVA from 0.82 +/- 0.30 to -0.11 +/- 0.06 logMAR (P<.0001). Regular astigmatism increased significantly from 0.53 +/- 0.23 D preoperatively to 0.63 +/- 0.40 D postoperatively (P =.0206). The asymmetry component increased significantly from 0.35 +/- 0.22 D to 0.64 +/- 0.40 D (P<.0001). Higher-order irregularity did not change significantly: 0.14 +/- 0.11 D before treatment and 0.17 +/- 0.20 D after treatment (P =.2166). The amount of myopic correction correlated significantly with the increase in the asymmetry component (Pearson correlation coefficient, R = 0.40, P =.0009) but not with the increase in regular astigmatism (R = 0.24, P =.055).
  
  
  CONCLUSIONS
  Irregular corneal astigmatism significantly increased, even in clinically successful orthokeratology cases. The effect of the changes on visual function should be studied further.
authors.affiliation: Matsumoto Eye Clinic, and 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: Airi
authors.initials: A
authors.lastname: Furuya
authors.forename: Yujiro
authors.initials: Y
authors.lastname: Matsumoto
authors.forename: Fumiki
authors.initials: F
authors.lastname: Okamoto
authors.forename: Norishige
authors.initials: N
authors.lastname: Sakata
authors.forename: Kentaro
authors.initials: K
authors.lastname: Hiratsuka
authors.forename: Tetsuhiko
authors.initials: T
authors.lastname: Kakita
authors.forename: Tetsuro
authors.initials: T
authors.lastname: Oshika
mesh_terms: D000293:Adolescent; D000328:Adult; D001251:Astigmatism / Q000209:etiology*; D002648:Child; D003261:Contact Lenses / Q000009:adverse effects*; D003315:Cornea / Q000473:pathology*; D019781:Corneal Topography; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D009216:Myopia / Q000628:therapy*; D011446:Prospective Studies; D013997:Time Factors; D014792:Visual Acuity