New techniques in glaucoma surgery

Recently, new techniques have been introduced for performing glaucoma surgery without opening into the anterior chamber, thus avoiding the complications which are commonly associated with penetrating glaucoma surgery. These methods involve exposure of the canal of Schlemm under a deep scleral flap without actually entering the anterior chamber and sometimes insertion of a collagen sponge under the scleral flap.1-4

Essentially these methods stem from the seminal work of Grant who demonstrated that in normal enucleated human eyes 75% of the resistance to aqueous outflow was located in the trabecular meshwork.5 Following Grant's work, various attempts were made to redesign glaucoma surgery to remove resistance at the trabecular meshwork thus lowering intraocular pressure. It is instructive now to reappraise these attempts.

Redmond Smith6 introduced the concept of trabeculotomy as surgery for open angle glaucoma and this was further developed by Harms and Dannheim.7 Soon after Grant's work Dvorak-Theobald and Kirk8 pointed out that some cases of open angle glaucoma were due to obstruction of the scleral collectors and Krasnov introduced sinusotomy for use in glaucoma when trabecular function appeared adequate.9 Sinusotomy and trabeculotomy were even combined to produced a filtering bleb with an intact anterior chamber.10

In 1968 John Cairns introduced trabeculectomy having noted the lack of acceptance of trabeculotomy.11 Essentially this functions as a guarded full thickness sclerectomy, although Cairns originally postulated that removal of trabecular meshwork would allow free flow of fluid into the open lumen of the canal of Schlemm bypassing trabecular resistance. There is now little doubt that trabeculectomy has supplanted all other forms of …