The concept of reducing intraocular pressure by way of surgery which preserves the internal trabeculum has recently enjoyed renewed interest.1-4 It mirrors an expanding body of reports proposing non-penetrating surgery as a viable alternative to conventional trabeculectomy in glaucoma management. Central to the appeal of this technique is the avoidance of ocular entry which obviates the need for an iridectomy and theoretically limits early postoperative hypotony. This in turn minimises the attendant sequelae of hyphaema, choroidal effusions, shallow anterior chambers, and cataract.

Non-penetrating surgery is broadly descriptive of two technical approaches. Deep sclerectomy, initially described by Krasnov,5 then Kozlov et al6 in slightly modified form, creates a Descemet's window that allows aqueous seepage from the anterior chamber. Subsequent fluid egress is thought to proceed subconjunctivally, resulting in a filtration bleb, as well as along deeper suprachoroidal routes. Further placement of a collagen implant in the scleral bed has been advocated to help maintain the scleral drainage reservoir.78 The second technique, viscocanalostomy, also requires deep scleral dissection and creation of a filtering window. Ultimate outflow, however, relies on the patency of putative aqueous exit channels, supposedly achieved through identifying and dilating Schlemm's canal using high density viscoelastic. Here, the superficial scleral flap is sutured down tightly, minimising subconjunctival fluid outflow and bleb formation.9

Current debate concerning the role of non-penetrating surgery as a successor to the gold standard trabeculectomy has revolved around its relative effectiveness in short to medium term intraocular pressure (IOP) control and safety.1011 Its justification will, however, have to be judged on the stage of randomised control trials12 that examine longer term IOP control, safety, and visual outcomes. Secondary issues relate to introducing a new surgical technique and involve audit, quality of life and cost considerations, and research into …