ABSTRACT

The advent of a new surgical procedure for glaucoma often raises the question of how the procedure lowers intraocular pressure (IOP), especially given the conventional understandings of the site of outflow resistance in glaucoma. Trabeculectomy was introduced in 1968 as a means of bypassing the clogged trabecular meshwork, allowing aqueous to enter Schlemm’s canal directly through the cut ends of the canal.1 Later experience found trabeculectomy most successful in cases in which a filtration bleb developed, giving rise to the understanding that it functions as a “guarded” filtration procedure.2,3 IOP can be lowered in the absence of a visible filtration bleb, however, indicating that the procedure may well allow aqueous to enter Schlemm’s canal directly in some cases, or alternatively that subclinical transconjunctival filtration of aqueous can occur.