title: Characterization of the aspheric corneal surface with intrastromal corneal ring segments.
abstract: OBJECTIVE
  Anterior corneal surface asphericity was examined in eyes of Phase II clinical trial participants, before and after intrastromal corneal ring segments (ICRS, Intacs) refractive surgery, and surveyed for relationship to clinical visual performance.
  
  
  METHODS
  Aspheric test objects with surface asphericity (Q) ranging from -0.01 Q to -1.44 Q and base radius of curvatures ranging from 7.5 mm to 9.0 mm were measured topographically using videokeratography. Radius of curvature asphericity profile plots were produced for test objects and compared to similar plots created for trial participant eyes (n=25) to quantify corneal asphericity. The potential effects of different amounts of corneal asphericity were assessed using measurement of uncorrected and spectacle-corrected visual acuity and photopic contrast sensitivity.
  
  
  RESULTS
  Preoperative corneal asphericity ranged from -0.01 Q to -0.81 Q and postoperative from -0.01 Q to -1.44 Q. Preoperative uncorrected visual acuity was significantly related to corneal asphericity; more myopic eyes tended to have more prolate corneal asphericity. Corneal asphericity was not significantly related to spectacle-corrected visual acuity or photopic contrast sensitivity, before or after surgery.
  
  
  CONCLUSIONS
  Postoperative corneal asphericity values demonstrated that intrastromal corneal ring segments (Intacs) produced a prolate aspheric surface for myopic correction from -1.00 D to -6.00 D. This study indicated that the range of corneal asphericity measured in these 25 eyes, before and after surgery, provided good visual acuity and normal contrast sensitivity.
authors.affiliation: Northwest Corneal Services and the Corneal Topography Research Center, Portland, Oregon 97223, USA.
authors.forename: D K
authors.initials: DK
authors.lastname: Holmes-Higgin
authors.forename: P C
authors.initials: PC
authors.lastname: Baker
authors.forename: T E
authors.initials: TE
authors.lastname: Burris
authors.forename: T A
authors.initials: TA
authors.lastname: Silvestrini
mesh_terms: D001672:Biocompatible Materials; D015350:Contrast Sensitivity / Q000502:physiology; D003319:Corneal Stroma / Q000503:physiopathology / Q000601:surgery*; D019781:Corneal Topography; D005500:Follow-Up Studies; D006801:Humans; D009216:Myopia / Q000503:physiopathology / Q000601:surgery*; D019736:Prostheses and Implants; D019919:Prosthesis Implantation; D014792:Visual Acuity / Q000502:physiology
chemical_list: D001672:Biocompatible Materials