Schlemm's canal after trabeculo-electropuncture (TEP).

The Schlemm's canals of two patients were examined histologically and electron-microscopically. The first patient had a tumor of the choroid. An electroprobe was inserted into the Schlemm's canal and then removed. In this eye, nearly all septa and almost the entire endothelial layer of the lumen were destroyed in the area of the inserted probe. The second tissue sample came from a patient who had had TEP surgery 2 years earlier and whose intraocular pressure had increased again. The preoperative gonioscopic examination showed an opening in the trabecular network, with blood evading from Schlemm's canal. Histologically, an opening approximately 50 micron wide, lined with endothelium, was found in the trabecular network. The lumen of the canal existed only in a section approximately 500 micron long. Elsewhere the inner and outer walls of the Schlemm's canal adhered to each other. In the area of this 500 micron long section of the canal, only one collector channel could be found. Thus, the insufficient decrease in intraocular pressure after operation can be explained by the side-effects of the insertion of the electroprobe into the Schlemm's canal.