TRABECULECTOMY PROCEDURES

There are measures that can be taken at every step of surgery that will help insure the best possible outcome from trabeculectomy procedures and avoid many common complications, according to Philippe Denis MD, Hopital de la Croix-Rousse, Lyon, France. “Trabeculectomy is currently the most effective primary glaucoma surgical procedure and certain refinements to the technique can improve the outcomes and improve the safety and reduce the risk of complications,” Dr Denis said at a Glaucoma Day session of the XXXI Congress of the ESCRS in Amsterdam.

For example, there are anti-metabolites that enhance filtration by preventing scar formation. There is also laser suture lysis or releasable sutures for greater early postoperative safety. In addition, there are a range of stents that provide a microconduit for the outflow of aqueous from the anterior chamber. Older style tube shunts like the Baerveldt and Ahmed devices produce similar results to trabeculectomy in terms of long-term safety and efficacy but have lower rates of re-operation. The devices are particularly useful in eyes undergoing cataract surgery, but are rarely indicated as a first-line choice.

Other techniques that rival trabeculectomy in terms of efficacy but have safety advantages are the non-penetrating techniques such as deep sclerectomy, which results in lower rates of hypotony but it is technically more demanding.

Preparing the eye

Dr Denis noted that when possible, it is best to stop eye drops before surgery because several studies have shown that long-term anti-glaucoma therapy is associated with increased rates of surgical failure and that the risk increases with the duration of treatment and the number of agents used. He noted that an important cause for the poor outcomes in patients receiving topical therapy over a long period is the result of the toxic effect of preservatives such as benzalkonium chloride.

However, benzalkonium chloride’s toxicity is reversible. Eyes can have a complete recovery of their corneal nerve network by four weeks after withdrawal of agents containing the preservative. (Sarkar J et al, Invest Ophthalmol Vis Sci. 2012;53(4):1792-802.) Pre-treating the eye before surgery with topical NSAIDs has been shown to increase this success of trabeculectomy. In eyes with neovascular glaucoma, intravitreal bevacizumab with or without panretinal photocoagulation can induce a reduction of the neovascularisation in the cornea and in the retina.

In eyes with inflammatory glaucoma with uveitis the optimal approach is to select a time for surgery when the uveitis has been quiescent for three months. However, in cases where the requirement for surgery is urgent, it is necessary to treat the inflammation aggressively to avoid a relapse, which can increase the risk of failure. In terms of anaesthesia, Dr Denis noted that although general anaesthesia may be the simplest approach it entails the risk of nausea and vomiting which can in turn increase the risk of choroidal haemorrhage.

Retrobulbar anaesthesia, meanwhile, carries the risk of optic nerve injury and it has limited effect on the conjunctiva. Local anaesthesia is generally less traumatic to the eye and enables the surgeon to tell the patient to move his head when necessary during surgery. Among the products available is lidocaine gel, which can be applied subconjunctivally with a cannula.

Surgical pearls

The best location for the conjunctival flap is at 12:00 at the limbus. This protects the bleb and reduces the risk of diplopia. In addition, placing a traction suture in the clear cornea helps prevent bleeding from the episclera. In cases of repeat trabeculectomy the choice of site should be guided by the conjunctival mobility test.

Dr Denis noted that conjunctival flaps have the advantage of healing rapidly, a greater distance between the conjunctival suture and the sclerectomy site, and, potentially, a reduced amount of bleb leaks. Fornix-based flaps have the advantage of being easier to perform because they provide better visualisation of the sclera. When using mitomycin-C, the agent should be applied at a concentration of 0.2 to 0.5 mg/ml for one to three minutes, followed by an intensive rinsing of the eye.

Some recent studies are showing anti- VEGF agents bevacizumab and ranibizumab delivered by various means may produce better results than mitomycin-C in terms of IOP and bleb morphology. The parameters that remain to be defined include the optimal dose, the route of administration and the time and duration of use, Dr Denis said. He noted that iridectomy cures pupillary block and prevents the risk of obstructing the ostium. However, it is not necessary in eyes undergoing combined procedures or in pseudophakic eyes.

Postoperatively, steroids are a mainstay of treatment for reducing inflammation. In eyes where the visual field loss is within 10 degrees of the fixation special postoperative care is necessary to avoid systemic and ocular hypotension in order to prevent the loss of the remaining visual field.

“Trabeculectomy is the mainstay of surgical treatment for glaucoma. Recent innovations are welcome, as it is important to improve our treatment and they may have an increasing role in the future. But for the time being, don't be afraid even in the most difficult case," Dr Denis advised.