PREFERRED SURGERY

When it comes to performing one- or two-site phacotrabeculectomy, evidence suggests outcomes are the same for most patients. But one- site phacotrabeculectomy may have an advantage in terms of preserving corneal health, reports Yvonne Buys MD, FRCSC, professor at the Department of Ophthalmology and Vision Sciences, University of Toronto, Canada.

"If you have a patient whose corneal health is of special concern, you may want to consider one-site," she told a session of the 5th World Glaucoma Congress where she reviewed the evidence for one- versus two-site phacotrabeculectomy plus discussed surgical approaches.

A randomised, controlled trial of 79 patients (which she co-authored), found when it came to IOP, visual acuity and the number of medications, there was no difference in outcome between one- and two-site patients. However, corneal endothelial cell counts proved to be better in the one-site patients at three and 12 months, with lower counts in the two-site patients.

"It's not surprising to see this kind of outcome. With one-site surgery you're a little bit more posterior entering the anterior chamber, and you're also having one less incision than in two-site surgery," she said.

She also co-authored a meta-analysis which showed that after three years of follow-up, there were no differences between one- and two-site surgery in lowering IOP, or in other measures. The only difference was that one-site surgery took less time to perform - on average by 13 minutes. The meta-analysis included studies with similar patient populations, an important detail in this type of study.

"Your choice comes down to what your preferred surgery is," she said. In her own practice, she prefers one-site phacotrabeculectomy and uses a corneal traction suture and subconjunctival anaesthesia with one per cent lidocaine. Dr. Buys incorporates the anaesthesia injection site into the conjunctival incision and does a fornix-based conjunctival flap. She noted it's important to dissect well posteriorally to create a pocket for fluid to drain into afterwards, and added that judicious cautery is important.

"I like to cauterize along the limbus as well, to try to encourage the anterior edge of that conjunctiva to stick down so that you minimise the risk of leaks," she said. For most cases she said she uses mitomycin, noting that various studies show mitomycin is associated with positive outcomes.

Sclera flap dissection   

She inserts a sponge soaked in mitomycin posteriorly under the conjunctiva before performing the sclera flap dissection. As for the flap, the design doesn't affect results though it should be approximately 1⁄2 sclera thickness. She usually creates a four-by-four millimetre triangular flap.

She uses a two-incision approach for the phaco, and suggests when performing combined procedures it is okay to leave some of the viscoelastic - as long as it's not behind the IOL. This reduces the risks of hypotony and lens-corneal touch.

In trabeculectomy alone she uses three sutures in the sclera flap, but in phacotrabeculectomy, she uses only two, with one being alongside the relaxing incision and the other at the apex. The flap shouldn't be too tight to allow drainage and preventing the conjunctiva from adhering to the sclera, she said.