Evaluation of Adverse Effects of Topical Glaucoma Medications on Trabeculectomy Outcomes Using the Glaucoma Medications Intensity Index

INTRODUCTION: Trabeculectomy is commonly performed for glaucoma when medications are unable to control disease progression or have intolerable adverse effects. Previous studies have suggested that a higher number of and/or longer treatment duration with preoperative topical glaucoma medications are associated with a higher risk of trabeculectomy failure, but most of these studies lack quantification of exposure. The aim of this study was to investigate the relationship between preoperative exposure to topical glaucoma medications and trabeculectomy outcome, using a new method for quantifying accumulated exposure. METHODS: Consecutive patients with primary open-angle glaucoma (POAG) or normal-tension glaucoma (NTG) who underwent primary trabeculectomy between 2013 and 2017 were retrospectively reviewed. The Glaucoma Medications Intensity Index (GMII) was calculated for each eye by multiplying the number of drops per week by duration of use (in years). The relationship between the GMII and postoperative outcome in terms of 1- and 2-year success rates and survival time was analyzed. RESULTS: A total of 55 eyes from 40 subjects were analyzed, all with follow-up > 6 months (mean 2.72 ± 1.46 years). The GMII for eyes with successful (n = 41) and failed (n = 14) outcome at last visit was 111.71 ± 78.59 and 167.41 ± 85.04, respectively, and significantly higher in failed eyes (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 (IOP), and GMII showed age and GMII to be possible predictors of treatment failure. On subsequent multivariate analysis, only GMII was correlated with failure (odds ratio 1.021, 95% confidence interval 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 needlings performed were higher (P = 0.03, P < 0.01, P < 0.03, respectively), and reduction in glaucoma medication was less (P = 0.02). CONCLUSION: The GMII can be used to predict eyes at higher risk for trabeculectomy that may benefit from additional perioperative intervention or treatment. It can also help the surgeon time the surgery before the GMII becomes too high, thereby optimizing the patient’s postoperative outcome.