Using the Glaucoma Medications Intensity Index (GMII) to predict trabeculectomy outcome

Abstract

Introduction Previous studies have reported that greater number and/or duration of preoperative topical glaucoma medications are associated with poorer trabeculectomy outcome, but the amount of exposure has never been accurately quantified. We aim to investigate the relationship between preoperative exposure to topical glaucoma medications and trabeculectomy outcome, using a new and more precise method for quantifying accumulated exposure. Methods Consecutive patients with primary open-angle glaucoma or normal-tension glaucoma who underwent primary trabeculectomy from 2013-2017 at a single centre were reviewed. The Glaucoma Medications Intensity Index (GMII) was calculated for each eye by multiplying number of drops per week by duration of use (in years). The relationship between GMII and postoperative outcome in terms of success rates and survival time was analyzed. Results Fifty-five eyes from 40 patients followed for 2.72 ± 1.46 years after primary trabeculectomy were analyzed. The GMII for successful eyes (n=41), 111.71 ± 78.59, was significantly lower than for failed eyes (n=14), 167.41 ± 85.04 (P=0.03). Univariate regression analysis of age, gender, cup-disc ratio, previous phacoemulsification, diabetes, hypertension, dyslipidemia, preoperative number of glaucoma medications / treatment duration / intraocular pressure, and GMII showed age and GMII as possible predictor for failure. On subsequent multivariate analysis, only GMII was correlated with failure (OR 1.021, CI 1.00-1.05, P=0.05). When GMII ≥80, the postoperative survival time was shorter (P=0.02), the 1-year IOP, number of glaucoma medications, and number of needling performed were higher (P=0.03, <0.01, 0.03, respectively), while reduction in glaucoma medication was less (P=0.02). Conclusion The GMII can help identify eyes with higher predicted risk for trabeculectomy failure, that may benefit from additional peri-operative intervention or treatment.