title: Effect of larger ablation zone and transition zone on corneal optical aberrations after photorefractive keratectomy.
abstract: OBJECTIVE
  To evaluate the effects of photorefractive keratectomy on corneal optical aberrations using a 5.5-mm optical zone and a 7.0-mm transition zone.
  
  
  METHODS
  Videokeratographs of 72 eyes from 47 patients treated for low to moderate (1-9 diopters) myopia were obtained at the preoperative and 1-, 3-, 6-, 12-, and 18-month postoperative examinations. The videokeratoscopy data files were used to calculate the wavefront variance of the corneas for small (3-mm) and large (7-mm) pupils using a previously described method.
  
  
  RESULTS
  In general, all optical aberrations decreased postoperatively for 3-mm pupils and increased for 7-mm pupils compared with preoperative values. For 3-mm pupils, the 2 common optical aberrations (comalike [S(3)] and spherical-like [S(4)]) decreased postoperatively and never returned to preoperative values. For 7-mm pupils, however, comalike aberrations increased slightly and spherical-like aberrations increased by nearly an order of magnitude during the postoperative period. Similarly, for 3-mm pupils, the higher order S(5) and S(6) aberrations decreased throughout the postoperative period, with S(6) values showing an approximately 23-fold reduction at 12 and 18 months. For 7-mm pupils, S(5) and S(6) aberrations increased slightly, more so for S(5) (approximately 3-fold) than for S(6). Total wavefront aberrations decreased an average of 2.3 times postoperatively for 3-mm pupils, and increased significantly (P<.05) at all postoperative examinations for 7-mm pupils. Opening the pupil from 3 mm to 7 mm before surgery produced a 14-fold increase in total aberrations, whereas this same change produced an average 113-fold increase after photorefractive keratectomy.
  
  
  CONCLUSIONS
  Corneal optical aberrations after photorefractive keratectomy with a larger ablation zone and a transition zone are less pronounced and more physiologic than those associated with first-generation (5-mm) ablations with no transition zone.
  
  
  CONCLUSIONS
  Evaluating the postoperative corneal aberration structure will help us devise ways to minimize the wavefront aberrations of the eye through the creation of an ideal corneal first surface, thereby improving visual results for patients undergoing excimer laser ablations for refractive correction.
authors.affiliation: LSU Eye Center, Louisiana State University Health Sciences Center, New Orleans, LA 70112-2234, USA.
authors.forename: M J
authors.initials: MJ
authors.lastname: Endl
authors.forename: C E
authors.initials: CE
authors.lastname: Martinez
authors.forename: S D
authors.initials: SD
authors.lastname: Klyce
authors.forename: M B
authors.initials: MB
authors.lastname: McDonald
authors.forename: S J
authors.initials: SJ
authors.lastname: Coorpender
authors.forename: R A
authors.initials: RA
authors.lastname: Applegate
authors.forename: H C
authors.initials: HC
authors.lastname: Howland
mesh_terms: D000328:Adult; D015350:Contrast Sensitivity; D003315:Cornea / Q000503:physiopathology* / Q000601:surgery; D019781:Corneal Topography; D006801:Humans; D054018:Lasers, Excimer; D008027:Light; D008875:Middle Aged; D009216:Myopia / Q000503:physiopathology* / Q000601:surgery; D018903:Photorefractive Keratectomy / Q000379:methods; D011680:Pupil; D014792:Visual Acuity