97th DOG Annual Meeting 1999



M. Walke 1, H. H. Becker 1, J. Saedler 1, D. G. Weiss 2

The investigation of morphological cell changes at phototherapeutic- (PTK) and photorefractive keratectomy (PRK) have the aim to reduce cell damages and molecular changes under the special aspect of an optimized ablation algorithm. The use of a suitable double fluorescence staining technique enables the registration of two to each other complementary pictures of living and dead cells. With a time resolved laser scanning microscopy technique (Nikon Diaphot 300/Odyssey) three dimensional cell structures are fast measurable together with a high spatial resolution.

Materials and methods: As a suitable model system for healthy human corneas we used freshly intact porcine corneas. The PTK- and PRK excimer laser ablation measurements were realized with an Chiron Technolas Ceracor 217. All washed corneas were stained in PBS with a LIVE/DEAD assay consisted of calcein AM (8 µM) and ethidium homodimer (8 µM) from Molecular Probes Inc. For data aquisition and evaluation we used the own Noran Intervision software of the laser scanning microscope (Nikon Diaphot 300/Odyssey argon-crypton-laser) and additionally a special three dimensional rendering software VOXELVIEW with VOXELMATH.

Results: The damage zone width on porcine trephanates after PTK and PRK corresponding is independent of the used frequency (2, 3, 5, 50 Hz). At the central point of the ablation area the layer width of dead cells reach about 1-2 cell layer into the stroma. At the edges of the ablation zone this dead cell zone reach about 2-4 cell layer into the stroma. At all possibly intensity settings of the Chiron Technolas laser system, we have not registered a significant changed dead cell layer width. The produced ablation patterns of the Chiron Technolas laser system are identical on corneas and special acryl materials. As expected the ablation patterns of different excimer laser systems are very different (Chiron Technolas Cerator and Coherent Schwind Ceratom)

1 Univ. Dep. of Opthalmology, Doberanerstr. 140, D-18055 Rostock 2 Univ. Rostock, Dep. Biology, Universitätsplatz 2, D-18057 Rostock