title: Registration tolerance of a custom correction to maintain visual acuity.
abstract: OBJECTIVE
  To present a predictive model of the registration tolerance for wavefront-guided correction to maintain acuity within fixed limits and demonstrate the potential utility using two typical keratoconic eyes.
  
  
  METHODS
  Change in log visual Strehl was plotted as a function of translation error for a series of rotations of a wavefront-guided correction. Contour lines were added at Δlog visual Strehl levels predicted to induce one- and two-line losses of logMAR visual acuity. The model was validated by regressing measured acuity loss from subjects viewing acuity charts that were degraded by the residual wavefront error resulting from the movement of wavefront-guided correction against the model's predicted acuity.
  
  
  RESULTS
  The model's predicted change in acuity can be substituted for measured change in acuity (R² = 0.91) within measurement error (±0.1 logMAR). Translation and/or rotation of a wavefront-guided correction induced asymmetric optical tolerance to movement. Induced errors depended on the wavefront error being corrected, the wavefront-guided correction design, and the amount of registration error.
  
  
  CONCLUSIONS
  Change in log visual Strehl can be used to determine the registration tolerance necessary to keep the variation in acuity within user-defined limits. This tolerance is unique for each wavefront error and wavefront-guided correction design.
authors.affiliation: *BMed †OD, PhD, FAAO ‡PhD §BS(Optom) ∥PhD, FAAO Visual Optics Institute (YS, RAA, XW, AR, HEB), College of Optometry, University of Houston, Houston, Texas.
authors.forename: Yue
authors.initials: Y
authors.lastname: Shi
authors.forename: Raymond A
authors.initials: RA
authors.lastname: Applegate
authors.forename: Xin
authors.initials: X
authors.lastname: Wei
authors.forename: Ayeswarya
authors.initials: A
authors.lastname: Ravikumar
authors.forename: Harold E
authors.initials: HE
authors.lastname: Bedell
mesh_terms: D000328:Adult; D057108:Corneal Wavefront Aberration / Q000503:physiopathology*; D006801:Humans; D007640:Keratoconus / Q000503:physiopathology*; D008875:Middle Aged; D008954:Models, Biological; D012160:Retina / Q000502:physiology*; D014792:Visual Acuity / Q000502:physiology*