Cylindrical tubules found spanning Schlemm’s canal

FORT LAUDERDALE, Fla. — Cylindrical tubular structures that span Schlemm's canal may be part of the mechanism that transports aqueous to the canal, according to a paper presented here.

Murray A. Johnstone, MD, and Robert Stegmann, MD, reported on the structures, identified in both the clinic and the laboratory, here at the Association for Research in Vision and Ophthalmology annual meeting.

In 10 human eyes undergoing viscocanalostomy, the authors noted structures spanning Schlemm’s canal during canal unroofing. Video documentation was used to assess the structures’ anatomic features. Diaphanous cylindrical structures, which by retroillumination could be seen to contain a lumen, spanned between the trabecular meshwork and the corneoscleral wall of Schlemm’s canal. The structures were highly compliant and by micromanipulation could be stretched to more than twice their resting length, the authors said. As many as 10 such structures were identified in an unroofed 5-mm region of Schlemm’s canal in children.

In the lab, the authors examined 16 necropsy eyes (8 human, 8 primate) in which viscoelastic was introduced into Schlemm’s canal. Five additional living rhesus monkey and 2 human autopsy eyes underwent experimental studies and were then examined by light, transmission and scanning electron microscopy. In both groups of eyes, light microscopy, TEM and SEM showed endothelial tubular channels originating from the trabecular meshwork. Their attachment to the corneoscleral wall of the canal and openings at their distal end could also be seen. Dilation of Schlemm’s canal with viscoelastic revealed diaphanous cylindrical structures spanning the canal, easily seen with the dissecting microscope, the authors said.