The changing conceptual basis of trabeculectomy: a review of past and current surgical techniques

The original intent of glaucoma surgery was to allow aqueous humor to exit more easily either through the sclera or into the suprachoroidal space. The former came to be called, generically, a glaucoma filtering procedure. As this surgery evolved, some explored the concept of lowering pressure without producing a hole in the sclera, with its resultant "filtering bleb." For example, Cairns hoped that cutting open the edges of Schlemm's canal would allow aqueous to leave without producing a filtering bleb; however, it became apparent that Cairns's "trabeculectomy" only worked when a filtering bleb developed. The goal of today's trabeculectomy is the creation of a longlasting transscleral fistula. In fact, trabeculectomy is a misnomer as excision of trabecular meshwork is unimportant. Frequently, the tissue excised to create a trans-scleral fistula is sclera, cornea, or both. The current trabeculectomy is really a guarded sclerokeratectomy. Newer techniques hope to increase aqueous outflow through Schlemm's canal to avoid complications associated with subconjunctival filtering blebs. Non-penetrating glaucoma surgeries (deep sclerectomy, viscocanalostomy) and ab interno trabecular surgery attempt to lower intraocular pressure with bleb-less procedures. We describe the recent evolution of glaucoma surgery, particularly the idea that intraocular pressure may be lowered satisfactorily without creating a filtering bleb.