GRAFT DECENTRATION IN PENETRATING KERATOPLASTY - NONMECHANICAL TREPHINATION WITH THE EXCIMER-LASER (193 NM) VERSUS THE MOTOR TREPHINE

BACKGROUND AND OBJECTIVE: Graft decentration is an obvious cause of po stkeratoplasty astigmatism. The purpose of this study was to compare g raft decentration after nonmechanical trephination with the excimer la ser (193 nm) with that after mechanical motor-trephination in 50 conse cutive patients with Fuchs' dystrophy and 50 patients with keratoconus . PATIENTS AND METHODS: To determine decentration in absolute values a nd clock hours, a postoperative slide was projected with a fixed magni fication onto a pattern with circles corresponding to the trephination margin. Using a second transparent and movable pattern with concentri c 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 ei ther method of trephination. RESULTS: The decentration was significant ly 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 limbu s [P < .01]; 0.64 +/- 0.24 mm, relative to the pupil [P < .005]). Ther e was no significant difference between the results obtained in patien ts with Fuchs' dystrophy and those of patients with keratoconus. The p referred direction of decentration relative to the pupil was the lower quadrants. There was a mild correlation between net astigmatism and t he absolute value of decentration. However, with sutures in place, the re were no significant differences in the keratometric net astigmatism between mechanical and nonmechanical trephination (P = .16) or betwee n Fuchs' dystrophy and keratoconus (P = .18). CONCLUSIONS: The results indicate that the amount of decentration can be reduced by specific t echniques associated with nonmechanical trephination. This might have a favorable impact on the residual astigmatism after suture removal.