title: Diurnal stability of refraction after implantation with intracorneal ring segments.
abstract: OBJECTIVE
  To investigate diurnal changes in visual acuity and refraction in myopic eyes implanted with intracorneal ring segments (ICRS).
  
  
  METHODS
  University of California San Diego Shiley Eye Center, La Jolla, California, and Emory University Vision Correction Center, Atlanta, Georgia, USA.
  
  
  METHODS
  This prospective study involved 2 groups of patients who had ICRS (Intacs) implantation and a follow-up of at least 6 months. The first group included 102 eyes of 51 bilaterally treated patients; the second group, 32 eyes of 16 unilaterally treated patients. Examinations including visual acuity, manifest refraction, and videokeratography were done in the morning and evening at least 9 hours apart on a single day. Refractive changes were analyzed by power vectors; multivariate statistics were used to determine the significance of change in any component of the spectacle prescription.
  
  
  RESULTS
  In the bilateral treatment group, 97 eyes (95%) were within 1 line of spectacle-corrected visual acuity from morning to evening. The mean change in manifest refraction was -0.14 +0.08 x 4 and in spherical equivalent, -0.10 diopters (D) (sigma = 0.3; range -0.750 to +0.875 D). Ninety-six eyes (94%) had a change in refraction within 0.50 D of spherical equivalent. There was no significant change in corneal power (P =.20). In the unilateral treatment group, there was no significant difference between treated and untreated eyes in changes in spectacle-corrected visual acuity, manifest refraction, or corneal power and toricity (P.05).
  
  
  CONCLUSIONS
  No clinically significant diurnal variation in visual acuity or manifest refraction was observed after ICRS implantation or in untreated paired eyes. Moreover, the data suggest less diurnal change in visual acuity and refraction after ICRS implantation.
authors.affiliation: Shiley Eye Center, Department of Ophthalmology, University of California San Diego, La Jolla, California 92093-0946, USA.
authors.forename: M D
authors.initials: MD
authors.lastname: Twa
authors.forename: T J
authors.initials: TJ
authors.lastname: Hurst
authors.forename: J G
authors.initials: JG
authors.lastname: Walker
authors.forename: G O
authors.initials: GO
authors.lastname: Waring
authors.forename: D J
authors.initials: DJ
authors.lastname: Schanzlin
mesh_terms: D002940:Circadian Rhythm / Q000502:physiology*; D003315:Cornea / Q000503:physiopathology / Q000601:surgery*; D019781:Corneal Topography; D006801:Humans; D009216:Myopia / Q000503:physiopathology / Q000601:surgery*; D010969:Plastics; D011446:Prospective Studies; D019736:Prostheses and Implants; D019919:Prosthesis Implantation; D012029:Refraction, Ocular / Q000502:physiology*; D016896:Treatment Outcome; D014792:Visual Acuity / Q000502:physiology*
chemical_list: D010969:Plastics