title: Eccentric small-zone ray tracing wavefront aberrometry for refraction in keratoconus.
abstract: OBJECTIVE
  To compare objective refraction using small-zone eccentric laser ray tracing (LRT) wavefront aberrometry to standard autorefraction in keratoconus (KC), and whether the visual acuities achieved with these refractions differ from corresponding values in healthy eyes.
  
  
  METHODS
  Twenty-nine eyes of 29 patients with KC and 29 eyes of 29 healthy controls were included in this prospective unmasked case-control study. The uncorrected (UCVA) and spectacle-corrected (SCVA) Early Treatment Diabetic Retinopathy Study (ETDRS) visual acuities based on refractions derived from LRT in central and four eccentric zones were compared to those achieved with standard autorefraction. The spherical equivalent (M) and two astigmatic power vectors (C0 and C45) were calculated for all refractions. Pentacam HR®was used to generate keratometry readings of the corresponding zones.
  
  
  RESULTS
  In KC, the refraction from the upper nasal zone rendered a higher SCVA than the standard autorefraction more often than in the controls (p < 0.001). There were no significant variation in M between the different LRT measurement points in the control group, but central data provided the best SCVA. The UCVA:s and SCVA:s were worse in KC, and the KC eyes showed inferior myopia and superior hyperopia. Multiple refractions rendered similar SCVA:s in KC. Pentacam HR®showed higher keratometry readings infero-temporally, but also lower readings supero-nasally, compared to controls.
  
  
  CONCLUSIONS
  In KC, eccentric LRT measurements gave better SCVA than standard autorefraction more often than in healthy eyes. Eccentric LRT may become a valuable tool in the demanding task of subjective refraction in KC.
authors: Department of Clinical Sciences/Ophthalmology, Umeå University Hospital, Umeå, Sweden.
authors: Anneli
authors: A
authors: Fredriksson
authors: Department of Clinical Sciences/Ophthalmology, Umeå University Hospital, Umeå, Sweden. anders.behndig@umu.se.
authors: Anders
authors: A
authors: Behndig
mesh_terms: D057128:Aberrometry; D000328:Adult; D016022:Case-Control Studies; D019781:Corneal Topography; D057108:Corneal Wavefront Aberration / Q000503:physiopathology*; D005260:Female; D006801:Humans; D007640:Keratoconus / Q000503:physiopathology*; D008297:Male; D011446:Prospective Studies; D012029:Refraction, Ocular / Q000502:physiology*; D014787:Vision Tests; D014792:Visual Acuity / Q000502:physiology*; D055815:Young Adult
keywords: autorefractometer; keratoconus; ray tracing wavefront aberrometry; refraction