title: Seven-year changes in corneal power and aberrations after PRK or LASIK.
abstract: OBJECTIVE
  To examine long-term changes in corneal power and aberrations in myopic patients randomized to photorefractive keratectomy (PRK) or laser in situ keratomileusis (LASIK).
  
  
  METHODS
  Forty-five patients with myopia from -6 to -8 diopters (spherical equivalent refraction) were randomized to PRK (n = 20) or LASIK (n = 25). Patients were examined preoperatively and for up to 7 years after surgery. Measurements included refraction, topography (TMS-1), and ultrasound pachymetry. By 3 years, 16 PRK and 15 LASIK patients were examined and by 7 years, 9 PRK and 7 LASIK subjects were available. Only patients who had not been reoperated and attended the two late controls were included in data analyses. Optical analysis of topographic data was used to calculate corneal power and wavefront aberrations.
  
  
  RESULTS
  PRK and LASIK caused a similar reduction in corneal power. During the first year after PRK, corneal power increased, but remained stable from 1 to 7 years. In contrast, corneal power continued to increase from 1 to 7 years after LASIK. Both PRK and LASIK caused an increase in coma-like and spherical aberrations that remained constant for 7 years. No significant changes in other higher-order aberrations were observed.
  
  
  CONCLUSIONS
  The cornea may not be stable even 7 years after LASIK, as indicated by the continuing increase in corneal power. In contrast, PRK appears stable from 1 year post surgery. Coma-like and spherical aberrations are permanently increased after PRK and LASIK. (ClinicalTrials.gov number, NCT00404105.).
authors.affiliation: Department of Ophthalmology, Aarhus University Hospital, Aarhus, Denmark. ai@dadlnet.dk
authors.forename: Anders
authors.initials: A
authors.lastname: Ivarsen
authors.forename: Jesper
authors.initials: J
authors.lastname: Hjortdal
mesh_terms: D000328:Adult; D003315:Cornea / Q000503:physiopathology*; D063171:Corneal Pachymetry; D019781:Corneal Topography; D057108:Corneal Wavefront Aberration / Q000503:physiopathology*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D020731:Keratomileusis, Laser In Situ; D054018:Lasers, Excimer / Q000627:therapeutic use*; D008297:Male; D008875:Middle Aged; D009216:Myopia / Q000503:physiopathology / Q000601:surgery*; D018903:Photorefractive Keratectomy; D012029:Refraction, Ocular / Q000502:physiology; D013997:Time Factors; D014792:Visual Acuity / Q000502:physiology; D055815:Young Adult