Objective: To study possible initial mechanisms of alterations in aqueous outflow that may result from the injection of viscoelastic into Schlemm's canal (SC) during viscocanalostomy.
Design: Experimental animal (Macaca nemestrina) and human autopsy study.
Methods: Eyes were dissected into a limbal ring and hemisected or quartered. Uncannulated segments served as controls. In treated segments, SC was cannulated and viscoelastic injected. Segments were fixed and sectioned into continuous 500 to 1000 microm pieces, examined at the dissecting microscope, and photomicrographs were taken. Representative tissue was further prepared for scanning electron microscopy or sectioned at 1 microm.
Main outcome measures: Tissue sections were examined to determine the extent of dilation and disruption of SC and related structures. SC dimensions were measured in segments from controls, cannulated regions, and regions of viscoelastic injection beyond the cannula insertion. In the hemisected segments, the circumferential extent of SC dilation was determined, and structures within the canal were described and counted.
Results: SC was dilated with increased anteroposterior length and height in cannulated and viscoelastic-injected segments in both primate and human eyes relative to untreated controls. The walls of SC were disrupted in both regions of cannulation and of viscoelastic injection, and the collector channels were widely dilated by viscoelastic. With decreasing effectiveness, the injected viscoelastic circumferentially dilated SC as far as 14 mm and 16 mm in primate and human hemisections, respectively. Structures that bridged between the walls of SC were often disrupted.
Conclusions: Cannulation of SC and injection of viscoelastic beyond the cannula resulted in marked dilation of SC and associated collector channels. Lateral walls, inner wall endothelium, and bridging structures of SC were frequently disrupted by cannulation and sometimes by injected viscoelastic. These findings suggest that viscocanalostomy may acutely cause a direct communication between SC and the juxtacanalicular space, and so may initially enhance conventional aqueous outflow. Controlled clinical trials will be necessary to determine the long-term outcomes of this procedure.