Combined trabeculectomy-cyclodialysis for glaucoma

May 1, 2015

The aim of modern glaucoma surgery is to reduce IOP by creating a drainage pathway for aqueous fluid. Trabeculectomy surgery has been modified over the years to prevent certain complications, however some still occur. In this article, the authors present a combined method of trabeculectomy with cyclodialysis as a potential option for glaucoma surgeons.

Take-home message: The aim of modern glaucoma surgery is to reduce IOP by creating a drainage pathway for aqueous fluid. Trabeculectomy surgery has been modified over the years to prevent certain complications, however some still occur. In this article, the authors present a combined method of trabeculectomy with cyclodialysis as a potential option for glaucoma surgeons.

 

By Dr Simon E. Skalicky, FRANZCO, and Dr Henry R. Lew, FRANZCO, FRACS

The aim of modern glaucoma surgery is to reduce intraocular pressure (IOP) by creating a drainage pathway for aqueous fluid. The guarded trabeculectomy is one common method of glaucoma drainage surgery, involving the formation of a sclerostomy guarded by a partial thickness scleral flap.1 The aim is for fluid to drain externally and collect in a subconjunctival bleb. Trabeculectomy surgery has been modified over time, including the use of antimetabolites (first 5-fluorouracil, later mitomycin C) to prevent bleb scarring and failure,2 and the use of releasable or adjustable sutures to fine-tune the postoperative drainage rate.3

With these modifications surgical outcomes have improved,4 yet complications can still occur including hypotony, cataract, dysesthesia, blebitis, corneal endothelial and limbal stem cell damage.5 In particular, the augmented trabeculectomy has a significant short- and long-term failure rate, limiting its success in long-term IOP control.6

Surgically induced cyclodialysis

Surgically induced cyclodialysis involves creating an anatomical plane between the ciliary body and inner scleral wall that connects the suprachoroidal space with the anterior chamber. The procedure is not new. First described by Sewall in 1907,7 surgically induced cyclodialysis achieved popularity in continental Europe and the US in the 1930s and 40s.8,9 However, in the following decades enthusiasm for the procedure declined due to postoperative hypotony, haemorrhage and anterior chamber collapse, as well as longer-term dialysis closure leading to IOP rise.10,11

Today a surgically-induced cyclodialysis is rarely performed by glaucoma surgeons due to concerns of the above complications. Hypotony often occurs as a result of a traumatic cyclodialysis, which can be difficult to close.12 However when the cyclodialysis is surgically induced the results are usually more predictable.13 Most surgeons have understandable concerns creating a surgically-induced cyclodialysis based on common clinical experience of traumatic cyclodialysis, but to equate the two is similar to equating a keratotomy for cataract surgery to a traumatic corneal laceration.

A surgically induced cyclodialysis is performed to create a controlled entry into the suprachoroidal space, a natural site for aqueous fluid to exit the eye trans-sclerally. Today this pathway is the target for procedures using intraocular microstents.12,13 In contrast to these ab-interno procedures, the combined trabeculectomy-cyclodialysis aims to direct flow not only into the suprachoroidal space, but also into Schlemm’s canal and the subconjunctival space under a tight scleral trapdoor similar to that used in a trabeculectomy.

Combined trabeculectomy-cyclodialysis

There are some theoretical advantages of combined trabeculectomy-cyclodialysis over the more commonly performed trabeculectomy. As internal and external drainage routes are created simultaneously, if one pathway closes due to postoperative scarring, the other may remain patent and maintain IOP control. The cyclodialysis enhances suprachoroidal flow and greatly augments the uveoscleral drainage pathway. This may lead to better 24-hour IOP control, as uveoscleral flow normally reduces greatly at night.14 In comparison drainage from a trabeculectomy is predominantly extraocular and bypasses both conventional and uveoscleral physiological pathways.

The procedure has been shown to be safe and reliable with good long-term outcomes in two clinical series. Sihota et al. reported good outcomes over a two year follow up period when used with mitomycin C for 45 Indian patients with post-penetrating keratoplasty glaucoma.15 We reported similarly good outcomes in a series of combined trabeculectomy-cyclodialysis augmented with 5-fluorouracil in 55 eyes from 39 patients over a 27-year period.13

Surgical technique

The procedure is as follows. A superior rectus muscle stay suture is used to rotate the globe inferiorly. A superior limbal-based conjuctival flap is performed. The initial conjunctival incision is right down to the episcleral space just anterior to the insertion of the superior rectus muscle. The introduction of closed Westcott scissors into this hole with blunt dissection medially and laterally allows conjunctiva, Tenon’s fascia and episclera to be lifted off the sclera together as a single layer extended forwards to the corneal limbus. The conjunctiva, Tenon’s fascia and episclera are further mobilized by passing closed Westcott scissors backwards on both sides of the superior rectus muscle and then opening them to create long posterior tunnels, as is commonly performed when exposing extraocular muscles in strabismus and retinal detachment surgery. This posterior mobilization makes it easier to close the conjunctival wound tightly; more importantly it creates long posterior passages for aqueous drainage backwards which may help to create a buffer against the formation of a subconjunctival ring of steel.

A 5x5 mm square superficial scleral trapdoor is dissected towards the cornea extending just beyond the surgical limbus [Figure 1(a)]. A 3x3 mm deep trapdoor is cut at the anterior end of the bed of the superficial trapdoor [Figure 1(b)]. Anteriorly it is opened through the cornea into the anterior chamber with an initial stab incision and then completed with Vannas scissors. Posteriorly its lateral margins are extended backwards to enter the suprachochoroidal space, exposing approximately 1 mm of ciliary body [Figure 1(c)]. An iris repositor is then used to separate the deep trapdoor from ciliary body at the scleral spur [Figure 1(d)] and to demonstrate that the suprachoroidal space is open [Figure 1(e)]. Any bleeding ciliary body vessels can then be treated with light diathermy under direct vision. The deep space thus created contains direct anatomical openings into Schlemm’s canal on each of its sides and a direct anatomical opening into the suprachoroidal space posteriorly.

A peripheral iridectomy is performed. The superficial trapdoor is sutured down at each posterior corner with a 10/0 nylon suture and then a small triangle is removed from the centre of its posterior edge to facilitate posterior drainage. Healon (Abbott Medical Optics, Abbott Laboratories Inc. Abbott Park, Illinois, USA) is injected under the superficial trapdoor to deepen the anterior chamber [Figure 1(f)];16 in addition some Healon is also injected into the posteriorly directed tunnels on each side of the superior rectus muscle.

The combined conjunctival, Tenon’s and episcleral wound is closed as a single full-thickness layer with two continuous 10/0 nylon sutures, each starting at opposite ends and crossing beyond the midline before being tied. This type of suture ensures the wound is watertight. A paracentesis is created and finally 5-fluorouracil 5 mg (0.1 mL) is injected in the sub-conjunctival space. Chloramphenicol ointment is placed on the outside of the eye. The eye is padded for 24 hours. In most cases, the 5-fluorouracil is repeated at three-daily intervals up to a total of five injections if tolerated.

Outcomes

Although there are no direct head-to-head studies comparing routine augmented trabeculectomy with combined trabeculectomy-cyclodialysis, our single-surgeon series13 can be compared to some of the larger augmented trabeculectomy series, in terms of complication rates, failure rates and glaucoma progression rates.4,17–21 Our series appears to have similar unqualified and qualified success rates: at completion of follow up mean IOP fell from 25.2 to 11.9 mmHg over a mean 11.2 years, 32 eyes (58.2%) achieved an unqualified success,18 (32.7%) a qualified success and 5 (9.1%) a failure. It is worth noting that two of these designated failures had pressures of 5 mmHg or less with no other detrimental symptomatology. No patient progressed to legal blindness.

Our series had a relatively high rate of post-operative cataract: 36 of 47 (77%) phakic eyes required cataract surgery following combined trabeculectomy-cyclodialysis; the majority occurred in the first four years. This is higher than reported in trabeculectomy patient cohorts with a similar mean age to this study. The reason for this high rate of cataractogenesis is unclear. It may be due to either early hypotony, or retention of viscoelastic in the anterior chamber at the end of the procedure, or both, perhaps producing hypoxia of the anterior lens surface. It may be due to the relatively advanced age of our cohort, for whom mean age was 70.1 years.

It may be that combined trabeculectomy-cyclodialysis tolerates cataract surgery better than does conventional trabeculectomy. In our series, patients requiring cataract surgery following combined trabeculectomy-cyclodialysis had mean IOP of 11.3 mmHg before cataract surgery; after cataract surgery mean IOP was 12.0 mm Hg: the difference was not statistically significant.

Hypotony was common in the early post-operative course. 27 (49%) and 16 (29%) eyes had IOP < 6 mmHg at weeks one and two respectively; this resolved within weeks in all but three cases. One case required needling for a flat bleb at four months postoperatively; three required bleb revision, one for hypotonous maculopathy and the other two for cystic, dysaesthetic blebs. One developed a flat AC postoperatively which resolved within 48 hours; one developed a hyphaema that resolved within the first week.

Indications

Currently there are no guidelines suggesting potential indications for this procedure. Drs S. and V. Gupta, (the latter a co-author from Dr Sihota’s paper), suggest the procedure be performed on refractory glaucomas, such as uveitic glaucoma, aphakic glaucoma, post vitrectomy and post penetrating keratoplasty glaucoma.22 There may be some merit in this suggestion, as trabeculectomy alone has higher risk of failure in such cases, and the combined trabeculectomy-cyclodialysis may avoid the need for a later drainage tube insertion. Given the relatively high rate of cataractogenesis the procedure may be better suited to pseudophakic patients.

Conclusion

Combined trabeculectomy-cyclodialysis, produces sustained lowering of IOP for long periods of time, despite a potential cataractogenic effect. The procedure may one day have a common role in the glaucoma surgeon’s repertoire; for now it is uncommonly performed due to concerns of increased risks, especially of hypotony. More work is needed to quantify the risks; however from the two series described13,15 the results seem relatively safe and predictable. The operation appears especially worthy of consideration when treating pseudophakic patients or those with refractory glaucoma and high risk of trabeculectomy failure.

 

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Dr Simon E. Skalicky, FRANZCO

E: seskalicky@gmail.com

Dr Skalicky is a Glaucoma and Cataract subspecialist at the Royal Melbourne Hospital and Royal Victorian Eye and Ear Hospital, University of Melbourne, Victoria, and a Clinical Senior Lecturer in the Discipline of Ophthalmology, University of Sydney, New South Wales, and Department of Surgery, University of Melbourne, Victoria, Australia.

Dr Henry R. Lew, FRANZCO, FRACS

Dr Lew was a Senior Ophthalmic Surgeon at the Repatriation (Veterans) General Hospital, Heidelberg, Melbourne from 1979-2007, where one of his major interests was the surgical treatment of glaucoma.

Drs Skalicky and Lew have no financial interests to declare.