Eyes with hypotony may fail less often after trabeculectomy

San Francisco-Eyes with hypotony after trabeculectomy might fare better than those without hypotony, a new study shows. 

If supported by further studies, the finding could change the way surgeons look at low IOP in glaucoma surgery, said Anne Coleman, MD, PhD, during the Shaffer-Hetherington-Hoskins Lecture at the 2016 Glaucoma 360 meeting.

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“We automatically say if you have a pressure of less than 5 [mm Hg] or less than 6 [mm Hg], you’re a failure,” said Dr. Coleman, director, Jules Stein Eye Institute Center for Community Outreach, University of California, Los Angeles. “Our results are showing that might not be the case-you might do at least as well as people who don’t have hypotony, maybe a little bit better.”

The definition of hypotony varies, with some authorities using an IOP of less than 6.5 mm Hg, and others at most 5 mm Hg.

In trials, investigators have measured the incidence at follow-up times of varying lengths after trabeculectomy. Partly as a consequence, incidence rates have ranged from 7.2% to 42.2% in observational studies and 1.6% to 12.4% in trabeculectomy clinical trials, Dr. Coleman said.

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Potential causes include overfiltration after trabeculectomy, bleb leaks, and decreased aqueous production by the ciliary body.

Anne Coleman, MD, PhD speaks with Ophthalmology Times at Glaucoma 360.

More on hypotony

Hypotony has been associated with decreased vision, maculopathy, choroidal effusions, suprachoroidal hemorrhages, corneal decompensation, peripheral anterior synechiae, cataract, and endophthalmitis.

Clinicians have treated it with efforts to reduce aqueous outflow or stimulate aqueous production, to induce scarring or remodel the bleb, or to place sutures over the bleb. They have also tried watchful waiting.

Yet, in studies published in the past 2 years, eyes with hypotony after trabeculectomy have maintained visual acuity as well as eyes without.

In their own trial, Dr. Coleman and her colleagues compared eyes with hypotony with a random sample of eyes without hypotony after trabeculectomy. They defined hypotony as an IOP of 5 mm Hg or less on three or more consecutive visits 3 months or more after trabeculectomy without bleb leak.

From 3,659 trabeculectomies performed between 1990 and 2014, they followed 88 cases of hypotony and 163 controls for a mean of 6.8 years.

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The patients were not significantly different in age, sex, or ethnicity. However, there were differences in glaucoma subtype. Most (88.6%) of the patients with hypotony had open-angle glaucoma, 2.3% had angle closure, and 9.1% had another subtype, whereas 73.6% of the controls had open-angle glaucoma, 19.9% had angle closure, and 13.5% had another subtype.

In addition, more of the eyes with hypotony were pseudophakic, and their mean preoperative IOP was 17.7 mm Hg, versus 20.4 mm Hg for the controls.

In the eyes with hypotony, the incidence of vision loss was 6.7 in 100 person years, and in the control eyes the incidence of vision loss was 7.7 in 100 person years. The difference was not statistically significant (p = 0.62) Rates of infection were also similar between the 2 groups.

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The incidence of failure was 9.6 eyes in 100 person years for the hypotony group versus 15.0 in the control group. The difference was on the boarder of significance (p = 0.05).

The investigators statistically adjusted for age, sex, ethnicity, glaucoma subtype, diabetes, hypertension, lens status, number of glaucoma medications, preoperative IOP, preoperative logMAR visual acuity, preoperative refractive error, laser suture lysis, the number of sutures in the scleral flap, and the surgeon performing the trabeculectomy.

In this analysis, they found that the eyes with hypotony had 45% of the failure rate of the control eyes (95% confidence interval hazards ratio 0.45 [0.25, 0.81]).

“So eyes with hypotony over the long run might actually be doing better than those eyes that don’t have hypotony,” Dr. Coleman said.

She cautioned that the researchers are still analyzing their data, and that more studies are needed.

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