Aims: To compare trabeculectomy with viscocanalostomy for the control of intraocular pressure (IOP) in open angle glaucoma (OAG) uncontrolled by medical therapy.
Methods: 48 patients (50 eyes) with uncontrolled OAG were randomised to either trabeculectomy (25 eyes) or a viscocanalostomy technique (25 eyes). Preoperatively, eyes were graded in terms of risk factors for drainage failure. Those undergoing trabeculectomy were given intraoperative antimetabolites (5-fluorouracil 25 mg/ml (5-FU), mitomycin C (MMC) 0.2 mg/ml and 0.4 mg/ml) according to a standard protocol. Antimetabolites were not used intraoperatively in eyes undergoing viscocanalostomy, but they were randomised to the use of viscoelastic (Healonid GV) for intraoperative intracanalicular injection.
Results: There were no significant differences between the groups in age, sex, type of OAG, preoperative medications, risk factors for drainage failure, and preoperative IOP. Mean follow up was 19 months (range 6-24 months). It was 12 months or longer in all eyes, except one lost to follow up at 6 months. At 12 months, complete success (IOP <21 mm Hg without antiglaucoma medications) was seen in all eyes undergoing trabeculectomy (100%), but in only 64% of eyes undergoing viscocanalostomy (p<0.00l). The mean IOP was lower at 12 months (p<0.001) with trabeculectomy and the number of eyes with IOPs of 15 mm Hg or less was greater (p<0.05). The mean IOP at 12 months was lower in eyes that had undergone viscocanalostomy using intraoperative intracanalicular Healonid GV injection compared to those where only balanced saline solution had been used (p<0.01). However, in terms of complete success there was no difference between the viscocanalostomy groups (p<0.1). With the exception of measurements at 1 week, visual recovery (logMAR acuity) was similar and laser flare and cell values showed little differences between the groups. Corneal topography and keratometry at 12 months were little different from preoperative values. Postoperative interventions (subconjunctival 5-FU and needling procedures) were similar between the groups. Transient complications such as early bleb leak and hyphaema were more common in the trabeculectomy group (p<0.05). Postoperative cataract formation was more common after trabeculectomy (p<0.05).
Conclusions: IOP control appears to be better with trabeculectomy. Viscocanalostomy is associated with fewer postoperative complications, although significant complications permanently impairing vision did not occur with either technique.
Surgical trabeculectomy has been the filtering procedure of choice for the management of glaucoma for the past 30 years. (1 2) It is quick, technically easy to perform, has fewer complications than full thickness procedures, and high reported success rates. (3-9) It is the standard by which all other filtering procedures should be judged. However, results are not always ideal. Early and late filtration failures are not infrequent, especially in eyes with risk factors for drainage failure (10-14) and sight threatening complications, such as endophthalmitis, suprachoroidal haemorrhage, hypotony, and cataract, occasionally occur. (1-9) To optimise results, frequent and careful outpatient monitoring is required, interventions such as suture release, lysis, and needling are not uncommon, and the adjunctive use of antimetabolites, with their associated problems, is now standard practice especially in eyes with risk factors for failure. (15-17)
Such limitations have led many investigators to explore other approaches to filtration surgery, including "non-penetrating trabecular" surgery. Epstein and Krasnov were the first to report such procedures, describing techniques in which Schlemm's canal was deroofed and conjunctiva sutured over the externalised canal. (18 19) Both reported short term success but poor long term results. In 1984 Zimmerman and colleagues reported "non-penetrating trabeculectomy," in which Schlemm's canal was deroofed under a partial thickness scieral flap. (20 21) In 1989 Fyodorov and Koslov described a modification of this procedure, utilising a collagen implant placed under the scieral flap, in an attempt to maintain drainage. They termed this "deep sclerectomy." (22 23) More recently, Stegmann has developed "viscocanalostomy," where following deroofing of Schiemm's canal and creation of a Descemet's window, viscoelastic is injected into the canal, in an attempt to bypass the trabecular meshwork while maintaining and opening th e normal anatomical drainage channels. (24)
The potential advantages of such techniques are that by avoiding penetration into the anterior chamber, intraocular complications such as overdrainage or endophthalmitis may be limited. In addition, as no iridectomy is required, the breakdown of the blood-aqueous barrier may be reduced, resulting in less anterior chamber inflammation with perhaps fewer cataracts, synechiae, and bleb failure and possibly a reduced need for antimetabolites. Finally, such surgery may not rely entirely on subconjunctival drainage, but allow aqueous to exit via Schlemm's canal and the normal anatomical outflow pathways and/or increase uveoscleral outflow.
Recent reports of such techniques have been encouraging. Using deep sclerectomy, Demailly reported a 76% success rate at 16 months, (25) but found no difference with the use of collagen implants. (26) While Sanchez reported a 70% success rate at 9 months, but found better results with collagen implants. (27) Similarly, Welsh reported an 87% success rate at 12 months (28) and Massey, in a study excluding eyes with risk factors for failure, an 81% success rate at 14 months. (29) However, Karlen, with longer term follow up of 36 months, reported a success rate of only 45% and used neodymium:yttrium-aluminium-garnet (Nd:YAG) laser goniopuncture in 40% to augment drainage. (30) Similarly, Hamard reported limited success of 60% and utilised goniopuncture in a third." With viscocanalostomy, Stegmann reported encouraging results with a success rate of 83% at 35 months in black African patients (24) and Carassa found similar success rates albeit with very limited follow up. (32) In all these studies, sight threatening complications were very infrequent.
Thus far there have been few studies comparing these techniques with trabeculectomy. Mermoud, in a retrospective study of deep sclerectomy with collagen implants versus trabeculectomy, found little difference in terms of overall success" and similar results were reported by El Sayyad in a prospective study of deep sclerectomy …