97th DOG Annual Meeting 1999
ERBIUM:YAG LASER ABLATION OF RETINAL TISSUE IN
INFLUENCE OF PULSE DURATION AND RADIANT EXPOSURE
T. A. Wesendahl, M. Franz, P. Janknecht
Purpose: It is our goal to examine the use of the Erbium:YAG-laser for the ablation of epiretinal membranes or the internal limiting membrane. We performed experiments in enucleated pig eyes to determine the parameters that might be important for in-vivo experiments and possible application in humans. In our study, the relationship between the tissue ablation depth and the parameters, pulse duration and radiant exposure, was analyzed.
Method: After dissection of pig globes at the equator and replacing the vitreous with perfluorocarbone liquid laser pulses of various energies were applied to the surface of the pig retina. Free running (t=250 µs, t=500 µs, t=750 µs) Erbium:YAG-laser energy was transmitted through a zirconium fluoride (ZrF4) fiber with a quartz tip (diameter 1 mm). The probe was elevated 1 mm ± 0,3 mm above the retinal surface. Radiant exposures were set to 1 J/cm2, 3 J/cm2, and 5 J/cm2.
Results: Tissue ablation (pulse duration t=250 µs) increased with radiant exposure in a linear fashion. 1 J/cm2, caused a tissue ablation depth of 3.2 ± 3.7 µm, 3 J/cm2 9.9 ± 7.0 µm, and 5 J/cm2 19.2 ± 6.4 µm. Comparable results were found using a pulse duration of 500 µs and 750 µs.
Conclusion: The Erbium:YAG laser produced precise ablation of the pig retina. Tissue ablation threshold is below 0.4 J/cm2. Our data implies that the retinal surface can be ablated using a radiant exposure of 1 J/cm2 without causing anatomical changes to the outer retinal structures. This is largely independent of the pulse duration.
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Univ. Bern, Institut für angewandte Physik, Sidlerstrasse 5, CH - Bern