title: Comparison of subjective visual acuity with visual acuity predicted from C-scan topography.
abstract: OBJECTIVE
  To compare the capability of objective measures of visual acuity (potential visual acuity from C-scan) to predict subjective visual acuity (best spectacle-corrected visual acuity [BSCVA]).
  
  
  METHODS
  Patients with BSCVA > or = 20/20 were enrolled in four groups (Group 1: normal [33 eyes]; Group 2: < -7.00 D myopia [43 eyes]; Group 3: > or = -7.00 D myopia [28 eyes]; Group 4: At least 1 month after LASIK [93 eyes]). Videokeratography was performed with the ray tracing Technomed C-scan. The potential visual acuity from C-scan was obtained with pupils undilated and intact precorneal tear films. All visual acuity was recorded in logMAR, and the significance of differences between acuities was assessed with a one-way ANOVA test.
  
  
  RESULTS
  The potential visual acuity from C-scan ray tracing of normal and myopic eyes in response to both photopic and mesopic stimuli did not differ. In a given eye, the potential visual acuity from C-scan ray tracing was better than BSCVA, and the difference was statistically significant. Although the potential visual acuity from C-scan of postoperative LASIK eyes in response to photopic stimuli was the same, it decreased under mesopic conditions.
  
  
  CONCLUSIONS
  Potential visual acuity from C-scan overestimates subjective visual acuity due to the inadequate assumptions in ray tracing or individual retinal resolution ability. In addition, the potential visual acuity from C-scan ray tracing varies with pupil diameter in different illumination.
authors.affiliation: Department of Ophthalmology, Taipei Municipal Jen-Ai Hospital, Taipei, Taiwan.
authors.forename: Show-Chuan
authors.initials: SC
authors.lastname: Tsai
authors.forename: I-Jong
authors.initials: IJ
authors.lastname: Wang
authors.forename: Shiow-Wen
authors.initials: SW
authors.lastname: Liou
authors.forename: Wei-Li
authors.initials: WL
authors.lastname: Chen
authors.forename: Yuan-Chieh
authors.initials: YC
authors.lastname: Lee
authors.forename: Gow-Lieng
authors.initials: GL
authors.lastname: Tseng
authors.forename: Fung-Rong
authors.initials: FR
authors.lastname: Hu
mesh_terms: D000293:Adolescent; D000328:Adult; D002648:Child; D003319:Corneal Stroma / Q000503:physiopathology / Q000601:surgery; D019781:Corneal Topography / Q000379:methods*; D006801:Humans; D020731:Keratomileusis, Laser In Situ; D008875:Middle Aged; D009216:Myopia / Q000503:physiopathology* / Q000601:surgery; D012029:Refraction, Ocular; D013524:Surgical Flaps; D014786:Vision Disorders / Q000175:diagnosis*; D014792:Visual Acuity / Q000502:physiology*