title: Graft decentration in penetrating keratoplasty: nonmechanical trephination with the excimer laser (193 nm) versus the motor trephine.
abstract: OBJECTIVE
  Graft decentration is an obvious cause of postkeratoplasty astigmatism. The purpose of this study was to compare graft decentration after nonmechanical trephination with the excimer laser (193 nm) with that after mechanical motor-trephination in 50 consecutive patients with Fuchs' dystrophy and 50 patients with keratoconus.
  
  
  METHODS
  To determine decentration in absolute values and clock hours, a postoperative slide was projected with a fixed magnification onto a pattern with circles corresponding to the trephination margin. Using a second transparent and movable pattern with concentric circles and ellipses, the authors measured the amount and direction of decentration relative to the limbus and to the pupil. In addition, the keratometric astigmatism and the refractive cylinder were assessed. In this prospective study, the patients were assigned randomly to either method of trephination.
  
  
  RESULTS
  The decentration was significantly lower (P < .002) with excimer laser trephination (0.23 +/- 0.26 mm, relative to the limbus; 0.33 +/- 0.26 mm, relative to the pupil) than with mechanical trephination (0.58 +/- 0.23 mm, relative to the limbus [P < .01]; 0.64 +/- 0.24 mm, relative to the pupil [P < .005]). There was no significant difference between the results obtained in patients with Fuchs' dystrophy and those of patients with keratoconus. The preferred direction of decentration relative to the pupil was the lower quadrants. There was a mild correlation between net astigmatism and the absolute value of decentration. However, with sutures in place, there were no significant differences in the keratometric net astigmatism between mechanical and nonmechanical trephination (P = .16) or between Fuchs' dystrophy and keratoconus (P = .18).
  
  
  CONCLUSIONS
  The results indicate that the amount of decentration can be reduced by specific techniques associated with nonmechanical trephination. This might have a favorable impact on the residual astigmatism after suture removal.
authors.affiliation: Department of Ophthalmology, University of Erlangen-Nürnberg, Erlangen, Germany.
authors.forename: A
authors.initials: A
authors.lastname: Langenbucher
authors.forename: B
authors.initials: B
authors.lastname: Seitz
authors.forename: M M
authors.initials: MM
authors.lastname: Kus
authors.forename: E
authors.initials: E
authors.lastname: Vilchis
authors.forename: G O
authors.initials: GO
authors.lastname: Naumann
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001251:Astigmatism / Q000209:etiology* / Q000473:pathology / Q000517:prevention & control; D003315:Cornea / Q000473:pathology* / Q000601:surgery; D005260:Female; D005500:Follow-Up Studies; D005642:Fuchs' Endothelial Dystrophy / Q000601:surgery; D006801:Humans; D007640:Keratoconus / Q000601:surgery; D015948:Keratoplasty, Penetrating / Q000009:adverse effects* / Q000379:methods*; D053685:Laser Therapy / Q000379:methods; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D011680:Pupil; D012029:Refraction, Ocular