title: Corneal asphericity and retinal image quality: a case study and simulations.
abstract: OBJECTIVE
  The optical quality of retinal images is dependent on the refracting elements of the eye including the nominally aspheric cornea and crystalline lens. This paper presents a retrospective theoretical analysis of the impact of corneal asphericity on the quality of retinal images. Clinical data are from the VISX Incorporated CustomVue IDE.
  
  
  METHODS
  Topography, contrast sensitivity, and visual acuity data were collected from 278 myopic eyes before and after wavefront-guided laser surgery. The measured corneal surface of each eye was fitted to a conic, and a Q-value was computed for a 5.5-mm pupil. A model eye was used to simulate various amounts of optical asphericity.
  
  
  RESULTS
  Preoperatively, most corneas exhibited negative conic shape constants. Postoperatively, corneas were about equally divided between positive and negative conics. There was no statistically significant correlation between the shape of the cornea and the subjects' perceptions of image quality including contrast sensitivity and visual acuity. Simulations showed that the corneal Q-value can vary from more to less prolate depending upon the shape of the internal surface.
  
  
  CONCLUSIONS
  Following wavefront-guided laser in situ keratomileusis (LASIK), contrast sensitivity is usually good and is not dependent upon the corneal conic shape. Better visual outcomes are more likely with a customized shape than a standard best conic shape.
authors.affiliation: VISX Incorporated, Santa Clara, CA 95051, USA. seemas@visx.com
authors.forename: Seema
authors.initials: S
authors.lastname: Somani
authors.forename: K Ashley
authors.initials: KA
authors.lastname: Tuan
authors.forename: Dimitri
authors.initials: D
authors.lastname: Chernyak
mesh_terms: D000328:Adult; D001251:Astigmatism / Q000175:diagnosis / Q000503:physiopathology / Q000601:surgery; D003198:Computer Simulation; D015350:Contrast Sensitivity; D019781:Corneal Topography; D005260:Female; D006801:Humans; D020731:Keratomileusis, Laser In Situ; D008297:Male; D008954:Models, Biological; D009216:Myopia / Q000175:diagnosis / Q000503:physiopathology / Q000601:surgery; D012160:Retina / Q000502:physiology*; D012189:Retrospective Studies; D014792:Visual Acuity