Risk Factors and Long-Term Outcomes in Patients with Low Intraocular Pressure after Trabeculectomy.

PURPOSE: To examine risk factors for low intraocular pressure (IOP) after trabeculectomy and to describe long-term outcomes in these eyes.

DESIGN: Retrospective case-control study.

PARTICIPANTS: Cases with low IOP included all patients with IOP ≤5 mmHg on 3 or more consecutive visits 3 months or later after trabeculectomy. Control patients without low IOP after trabeculectomy were randomly selected at a 1:2 case-to-control ratio.

METHODS: A case-control study was performed of patients undergoing trabeculectomy at the Stein Eye Institute. Covariates included demographics, history of cataract surgery, refractive error, number of glaucoma medications, family history of glaucoma, diabetes, hypertension, visual acuity (VA), IOP, number of sutures in the scleral flap, laser suture lysis, surgeon, and laterality of surgery. Logistic regression modeling was used to examine associations between each covariate and low IOP. Postoperative outcomes that were examined included reoperation, vision loss, and surgical failure. The time between trabeculectomy and each outcome was compared between cases and controls with Cox proportional hazards regression modeling.

MAIN OUTCOME MEASURES: Low IOP after trabeculectomy, reoperation, vision loss, and surgical failure.

RESULTS: Of 3659 total trabeculectomies performed by 5 surgeons between 1990 and 2013, 64 eyes had low IOP (1.7%), which were compared with 130 control eyes. Fifteen of the 64 eyes with low IOP had hypotony maculopathy (23.4%). After accounting for differences in baseline IOP, laser suture lysis was negatively correlated with low IOP after trabeculectomy (odds ratio [OR], 0.33; 95% confidence interval [CI], 0.13-0.87); surgeon was correlated with high vs. low IOP after trabeculectomy (OR, 5.32; 95% CI, 1.53-18.52). There were no statistically significant associations between low IOP and time to reoperation (hazard ratio [HR], 0.73; 95% CI, 0.32-1.68), vision loss (HR, 1.77; 95% CI, 0.81-3.88) or surgical failure (HR, 1.14; 95% CI, 0.62-2.11). In patients with low IOP, there was a higher unadjusted incidence of bleb revision in patients who had maculopathy (7.6 vs. 1.9 revisions/100 person-years; for maculopathy versus no maculopathy P = 0.008).

CONCLUSIONS: The absence of laser suture lysis and surgeon are factors potentially associated with low IOP after trabeculectomy. Numeric hypotony does not necessarily represent clinical failure after trabeculectomy.