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Impressum
Histopathologic investigation of Schlemm`s Canal and the Trabecular Meshwork after Laser Canalostomy (LC) and Excimer Laser Trabekelablation (ELT)
Specht H., Burk R. O. W. , Völcker H. E., Kruse F. E.
Universitäts-Augenklinik Heidelberg
Introduction: There are different attempts to Lower the intra
ocular pressure by laser surgery. We compared Laser Canalostomy
(LC) and Excimer Laser-Trabecularablation
(ELT), concerning their effect on the histological appearance of
the endothelium of Schlemm`s Canal and on the trabekular meshwork.
Method: After a non penetrating deep sklerectomy LC was performed
on five human donor eyes in vitro. The LC probe (diameter 200µm
to 300 µm) allowed probing of Schlemm`s Canal ab externo. The radius
of the probe followed the curvature of Schlemm`s Kanal. The ELT was performed
ab interno on three human donor eyes in vitro. The probe used had an outside
diameter of 500µm. The laser used for photo ablation with both applications
was a Excimer laser of the Glautec AG, with a wavelength of 308nm. The
pulse length was 80ns, repetition rate and energy was adjustable. The
preparations were examined histological and by scanning electron microscopy.
Results: The number of pulses necessary for the complete perforation
of the trabecular meshwork with ELT was 20±2 pulses and with LC
40±5. The energy output at the fiber was 1.2 mJ. ELT induced mechanical
damages of the trabecular meshwork, caused by physical manual contact
with the ELT probe. Holes created by LC had an oval shape due to the output
mirror which has an angle of 40°.
Conclusion: Both procedures are suitable for the initialization
of the trabecular meshwork. LC permits a controlled ablation of endothelium
of the internal wall of Schlemm`s Canal with a smaller damage of the trabecular
meshwork. However the surgical procedure is mutch more complicated than
ELT. Further studies are needed to evaluate the reduction of outflow resistance,
created by both techniques. Consequently wound healing responses following
laser surgery to the trabecular meshwork need to be studied.