title: Morning-to-evening change in refraction, corneal curvature, and visual acuity 11 years after radial keratotomy in the prospective evaluation of radial keratotomy study. The PERK Study Group.
abstract: OBJECTIVE
  Previous reports demonstrate morning-to-evening changes in ophthalmic measurements at 3 months, 1 year, and 4 years after radial keratotomy. The authors determine whether diurnal change in refractive error persists 11 years after radial keratotomy surgery in the Prospective Evaluation of Radial Keratotomy (PERK) study.
  
  
  METHODS
  Seventy-one patients were examined in the morning and evening a mean of 11.1 +/- 0.6 years (range, 10-12.7 years) after undergoing radial keratotomy under a standardized protocol using a diamond blade.
  
  
  RESULTS
  Between the morning and evening examinations, the mean change in the spherical equivalent of refraction was a 0.31 +/- 0.58-diopter (D) increase in minus power in first eyes. Thirty-six (51%) eyes had an increase in minus power of the manifest refraction of 0.50 to 1.62 D; 22 (31%) had a change in refractive cylinder power of 0.50 to 1.25 D; 9 (13%) had a decrease in uncorrected visual acuity of two to seven Snellen lines; and 25 (35%) showed central corneal steepening measured by keratometry of 0.50 to 1.94 D. Two (3%) eyes lost two lines of spectacle-corrected visual acuity, whereas one (1%) eye gained two lines. In patients whose both eyes underwent surgery, a high degree of symmetry was observed in morning-to-evening refractive change.
  
  
  CONCLUSIONS
  In some patients after radial keratotomy, morning-to-evening change of refraction and visual acuity persists for at least 11 years, although in most patients the magnitude of this change is small. Thus, diurnal fluctuation may be a permanent sequela of radial keratotomy in some individuals.
authors.affiliation: Doheny Eye Institute, University of Southern California School of Medicine, Los Angeles, USA.
authors.forename: P J
authors.initials: PJ
authors.lastname: McDonnell
authors.forename: A
authors.initials: A
authors.lastname: Nizam
authors.forename: M J
authors.initials: MJ
authors.lastname: Lynn
authors.forename: G O
authors.initials: GO
authors.lastname: Waring
mesh_terms: D002940:Circadian Rhythm; D003315:Cornea / Q000473:pathology*; D005500:Follow-Up Studies; D006801:Humans; D007646:Keratotomy, Radial / Q000009:adverse effects*; D011183:Postoperative Complications / Q000209:etiology*; D011446:Prospective Studies; D012029:Refraction, Ocular; D012030:Refractive Errors / Q000209:etiology*; D014792:Visual Acuity; D014945:Wound Healing