Vertical tilt after penetrating keratoplasty - Comparison between nonmechanical trephination with the excimer laser and motor trephination

Langenbucher, A.; Seitz, B.; Kus, M.M.; Naumann, G.O.H.

Klinische Monatsblaetter fuer Augenheilkunde 212(3): 129-140

1998


Accession: 008010898

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Abstract
Background: Besides decentration of the graft/host trephination and "horizontal torsion" "vertical tilt" is an important factor for reduced visual outcome after penetrating keratoplasty (PK). The purpose of this study was to evaluate the time course of vertical tilt in absolute value and direction and to correlate it with functional results after PK. Patients and methods: Fifty patients each (20 primary dystrophies, 30 keratoconus) underwent nonmechanical trephination (NMT) (excimer laser MEL60, Aesculap-Meditec, Heroldsberg, Germany) or mechanical motor trephination (MT) (Geuder, Heidelberg, Germany) in penetrating keratoplasty. All procedures (7.5 mm in dystrophies, 8.0 mm in keratoconus, 8 orientation teeth in NMT, double-running 10-0 nylon suture) were performed by one surgeon (GOHN). At a postoperative gate of 6 weeks, 6 months, before partial suture removal and after complete suture removal, corneal topography analysis (TMS-1, Tomey, Tennenlohe, Germany) was performed. After a Gram-Schmidt-orthogonalization corneal topography height data of 25 noncentric rings in 256 hemimeridians were decomposed into Zernike components of radial order n = 16 in the sense of minimizing the root mean square error. The tilt of the surface relative to the videokeratoscope axis was calculated from the Zernike components Z11 and Z1-1. The meridional power at the cardinal meridians was derived from all parabolic Zemike terms. Tilt and the difference between both meridians of the Zemike representation (ZA) were correlated with the results of Zeiss keratometry (KA), Simulated Keratometry (SimK) of the TMS-1, subjective refraction (RZ) and best-corrected visual acuity. Results: After NMT, vertical tilt of the graft was 3degree without significant change over time. Following MT, an equivalent time course could be observed before partial suture removal. However, after complete suture removal, a significant increase of the tilt was measured to 5degree (p = 0,02). No significant difference could be detected comparing keratoconus and Fuchs' dystrophy both in NMT and MT. The direction of the vertical tilt component piled up to the hemimeridian defined by the knot of the first running suture. At all postoperative follow-up examinations, the ZA of the Zemike decomposition showed a good correlation to the RZ, whereas the KA and the SimK did not. At the end of the follow-up, best-corrected visual acuity after NMT was 2 decimal lines better than after MT.