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Fornix and limbus flap incisions for glaucoma implant provide comparable efficacy
Each technique has distinct advantages and disadvantages, so surgeon preference plays a role in which method is used.
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Glaucoma surgeons who implant a nonvalved drainage device can safely use either fornix-based or limbus-based incisions, according to a study.
A retrospective study of 160 eyes of 147 glaucoma patients has found that long-term IOP is similar for either fornix-based or limbus-based incisions. The study also concluded that medication burden and visual acuity were similar for the two flap techniques; however, eyes in the fornix group were more likely to develop endophthalmitis or undergo subsequent tube revision, although incident rates for these two surgical complications were not significantly different from the limbus group.
Michele C. Lim, MD, a professor of ophthalmology at the UC Davis Health System Eye Center and co-author of the study, which appeared in Journal of Glaucoma, said she and her colleagues were partially inspired by the Tube Versus Trabeculectomy Study.
“Most of the surgeons who participated in the surgery for that study used the fornix-based approach to insert a tube, while only a minority of surgeons used the limbus-based approach,” Lim told Ocular Surgery News. “That study also did not evaluate whether a particular approach affected the outcomes.”
The investigators of the current study felt that the limbus technique would result in worse outcomes because the incision is basically placed right where the bleb is supposed to form over the plate, Lim said.
“This, theoretically, could cause a lot of scarring in the area where you want the tissue to be very functional to provide a little bit of resistance but not too much resistance to flow,” she said.
Hence, it was a surprise that the limbus approach performed as well as the fornix approach, Lim said.
“Because of the theory of wound healing, you would expect the pressures to be higher in the limbus group,” she said.
Limbus vs. fornix
Each study eye received a 350-mm2 Baerveldt glaucoma implant (Abbott Medical Optics), with 69 eyes in the limbus group and 91 eyes in the fornix group.
At 2-years’ follow-up, mean IOP was 14.3 mm Hg in the limbus group and 13.1 mm Hg in the fornix group.
At the final visit (range: 1 year to 5 years), the overall success of IOP control was 90% in the limbus group and 87% in the fornix group.
The number of medications was reduced significantly in both groups, from 3.03 at baseline to 1.6 at 2 years in the limbus group and from 2.8 at baseline to 1.3 at 2 years in the fornix group.
Changes in visual acuity were also comparable, as reflected in a loss of two or more lines. In the limbus group, this occurred in 19% of eyes from baseline to 12 months, 28% of eyes from 12 months to 24 months, and 60% of eyes from baseline to the last visit; in the fornix group, the percentages were 36%, 37% and 42%, respectively.
Surgeon preference
Although each technique has advantages and disadvantages, Lim said it boils down to individual surgeon preference.
“A limbus-based incision is easier for identifying the muscles in the eye, so that you can place the implant under the muscles,” Lim said. “Another advantage is that the incision site is away from the cornea; therefore, you are not placing sutures where the patient will really feel them. Theoretically, this promotes comfort in the postop period for the patient.”
Conversely, she said, “When you actually make the hole into the anterior chamber of the eye, it is harder to see at the limbus of the eye. … This makes it harder for the needle to pass through and for the passage of the tube.”
An advantage of the fornix approach is that the limbus is in plain view for making the sclerotomy and passing the tube.
“But the disadvantage,” Lim said, “is that you are placing sutures at the limbus, which can cause the patient more discomfort.”
The fornix technique also benefits the patient who has conjunctival scarring from previous surgery or trauma.
“This approach makes it easier to dissect the conjunctiva,” she said. – by Bob Kronemyer