Viestenz A., Seitz B., Langenbucher A., Viestenz A., Ferreira de Souza R., Küchle M.

Department of Ophthalmology, University of Erlangen-Nürnberg, Erlangen, Germany

Background: The purpose of this study was to assess the impact of an automatic laser beam control for the Er:YAG solid state laser (2.94 µm) on the cut performance and thermal damage zone in nonmechanical corneal trephination.
Methods: Twenty-eight linear cuts along metal slit masks (slit size 2.5x0.4 mm) were performed with a q-switched laser (spot size 0.7 mm, repetition rate 5 Hz). We compared the macroscopic image and the histologic sections (PAS-staining) of 1) a manually guided laser beam via micromanipulator ("joystick"), 2) the semi-automatically guided laser beam with a triangular analogous trigger signal and 3) a fully PC-controlled digital laser beam positioning system with fine tuning and position feed-back.
Results: Macroscopically, an irregular cut surface with tissue remnants and inhomogeneous cut depth (between 10 and 100% of the stromal thickness =perforation) was observed. In the semi-automatically laser beam control, the inhomogeneity of cut depth (80-100%) and tissue remnants were much less pronounced. Using the PC-controlled laser positioning system a fully homogeneous cut depth could be reached. The manually guided laser beam control induced the broadest thermal damage zone in the corneal stroma (19.3±8.7 µm) compared to the semi-automatical mode (8.8±3.0 µm, p=0.03) and the PC-controlled laser beam control (7.0±3.0 µm, p=0.016).
Conclusions: The fully automatical PC-controlled laser beam positioning system for the Er:YAG solid-state laser with a small spot size and low repetition rate allows a precise laser beam guidance and a significant enhancement of the cut performance compared to a manual laser beam control via micromanipulator in experimental nonmechanical corneal trephination.

Copyright © Deutsche Ophthalmologische Gesellschaft, 2001. All rights reserved.

Last updated: 

Webdesign: SPALLEK.COM