REGULARITY OF CORNEAL TOPOGRAPHY AFTER PE NETRATING KERATOPLASTY - NONMECHANICAL TREPHINATION WITH THE EXCIMER-LASER 193 NM VS MECHANICAL TREPHINATION

Background ''Vertical tilt'' of the graft caused by incongruent cut an gles, ''horizontal torsion'' caused by a asymmetric suturing and decen tration oi: the wound seem to be the most important reasons for high a nd/or irregular postoperative astigmatism and deterioration of visual outcome after penetrating keratoplasty. We studied the time course of qual il alive and quantitative topographic criteria after nonmechanica l and mechanical trephination in correlation with visual outcome. Pati ents and methods Fifty patients each (30 keratconus, 20 Fuchs' dystrop hies) underwent nonmechanical trephination (excimer laser MEL60, Aescu lap-Meditec, Heroldsberg) and mechanical motor-trephination in penetra ting keratoplasty. All procedures (7.5 mm trephination diameter in Fuc hs, 8.0 mm in keratoconus, double-running 10-0 nylon suture) were done by one surgeon. Pre-, intra- and postoperative treatment were identic al. At the follow-up examinations, the keratometric astigmatism, quali tative and quantitative criteria of the automatic videokeratography, v isual acuity and refraction were assessed. In addition, vector-correct ed astigmatism (Jaffe-model) was evaluated in the postoperative time c ourse, particularly after suture removal Results After a mean follow-u p of 1.1 +/- 0.8 years, keratometric net astigmatism was 4.0 and 4.2 d iopters after nonmechanical and mechanical trephination. Corneal topog raphy analysis showed a higher orthogonality of the bow-tie shape and less asymmetry between opposite hemimeridians. Vector-corrected change s of corneal astigmatism were less after complete suture removal in no nmechanical trephination. After nonmechanical trephination. visual acu ity was 2 decimal lines better. Discussion Nonmechanical trephination with the excimer laser 193 nm has the potential to improve the visual outcome by creating smooth and congruent cut edges parallel to the opt ical axis and the application of ''orientation teeth''. Since corneal net astigmatism does not differ significantly, a higher regularity of corneal topography after excimer laser trephination is supposed to be a main reason for this finding.