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Trabeculectomy yields lower IOP than viscocanalostomy
Trial in 50 eyes compared the procedures head-to-head in a randomized design.
MILAN, Italy — Results of a 2-year study comparing viscocanalostomy to trabeculectomy show greater intraocular pressure (IOP) reductions for patients receiving standard trabeculectomy.
Roberto Carassa, MD, and colleagues randomized 50 eyes to undergo standard trabeculectomy or viscocanalostomy to compare the IOP-lowering effects of viscocanalostomy to standard trabeculectomy.
Viscocanalostomy is a non-penetrating technique aimed at restoring the physiological outflow pathway. It has been gaining increasing interest in recent years, said Dr. Carassa, an assistant clinical professor of ophthalmology at the University of Milan.
Both techniques provided IOP control over time, he said. The short-term IOP decreases with trabeculectomy were greater within the first 6 months with some leveling off thereafter, he told fellow physicians.
"Trabeculectomy assured significantly lower IOP, but only at 2, 3 and 6 months due to an increasing trend over time of the IOPs in this group," he said.
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IOP comparisons
"When considering the Kaplan-Meier cumulative probability of success for an IOP between 6 mm Hg and 21 mm Hg and on no medication, the success of the trabeculectomy was greater than the viscocanalostomy at all time intervals," Dr. Carassa explained.
"Nevertheless, the difference now becomes significant by excluding the four initially unsuccessful cases biased by intraoperative complications," he continued.
"Therefore, we can say that if viscocanalostomy is carried out properly, and is successful in the first few days, its success is satisfactory and stable over time. Nevertheless, if we assume for success an IOP reduction between 6 mm Hg and 16 mm Hg, trabeculectomy demonstrates a clear-cut greater success than viscocanalostomy, given the fact that it indeed yields lower IOP," he said.
Study details
Mean postoperative final IOP was 13 mm Hg in the viscocanalostomy group, Dr. Carassa reported.
The prospective and randomized study included patients judged to be good surgical candidates for trabeculectomy, regardless of their final group assignment. Patients had primary open-angle glaucoma or pseudoexfoliative glaucoma and were 45 years old or older.
"All the procedures were done by the same operator who was trained and experienced in viscocanalostomy," he said.
Suturlysis and 5-FU injections in the trabeculectomy group during the postoperative interval were allowed; goniopunctures, needlings (for encapsulated blebs) and suturlysis were not, and represented surgical failure in the viscocanalostomy group, Dr. Carassa said.
Due to intraoperative complications, three cases were deemed immediate surgical failure, though he did not provide further details as to the nature of the complications. Typical postoperative problems his team encountered in trabeculectomies were transient hypotony with peripheral choroidal detachments and punctate keratitis from 5-FU injections for encapsulated blebs, he continued.
Bleb formation
Bleb filtration occurred in about 33% of the viscocanalostomy procedures, as confirmed by regular and ultrasonic biomicroscopy. "Although the technique should avoid bleb formation, we found some external filtration in one-third of the cases," Dr. Carassa said.
Aside from these intraoperative procedures, viscocanalostomy is "characterized by very little side effects," he said.
Patient comfort
Patients were queried throughout the follow-up process as to eye comfort, and those in the viscocanalostomy group seemed more satisfied, Dr. Carassa reported.
"The trabeculectomy group was characterized by a larger number of unscheduled visits and greater eye discomfort, as could be expected considering the frequency of 5-FU injections and bleb formation," he said.
Nine of the trabeculectomy patients received 5-FU injections, he added.
Postoperative complications are minor and fewer in viscocanalostomy patients compared to trabeculectomy patients. "Postop management is easier and requires less number of visits," he said.
Some thoughts at two years
The procedure offers good IOP reductions, though "higher than expected" when compared to conventional trabeculectomy. It is more difficult and time-consuming to perform as well, Dr. Carassa said.
"Viscocanalostomy seems a promising procedure … nevertheless, larger long-term controlled studies are needed in order to define the role that these new surgeries will have in the management of glaucoma," he said.
For Your Information:
- Roberto Carassa, MD, can be reached at HS Raffaele, Olgettina 60, Milan, 20132, Italy: (39) 02-2643-3598; fax: (39) 02-2641-2912; e-mail: carassa@tin.it.