The Effect of Preoperative Preservative Burden on the Success of Ab-Interno Trabeculotomy.

PURPOSE: To evaluate the effect of preoperative cumulative preservative burden on 1 year surgical outcomes of Kahook Dual Blade (KDB) and Gonioscopy-Assisted Transluminal Trabeculotomy (GATT). METHODS: This retrospective study included 46 eyes (23 KDB, 23 GATT). A Preservative Burden Index (PBI) was calculated by incorporating specific concentrations of preoperative topical preservatives. Main outcomes were 1-year complete and qualified success rates. Receiver operating characteristic (ROC) analysis determined the optimal PBI cut-off. Kaplan-Meier analysis and multivariable Cox regression identified independent risk factors for surgical failure. RESULTS: Preoperative PBI was significantly higher in the GATT group than the KDB group (0.71 ± 0.43 vs. 0.34 ± 0.32, p < .001). At 1 year, complete success was 43.4% for KDB and 8.7% for GATT, while qualified success was high in both (91.3% and 100%, respectively). ROC analysis identified a critical PBI cut-off of 0.36 predicting surgical failure. Kaplan-Meier analysis showed significantly lower surgical survival in patients exceeding this threshold. Multivariable Cox regression confirmed surgical technique (KDB vs. GATT) was not a significant failure predictor (HR = 2.15, p = .1). Instead, a low PBI significantly reduced the hazard of failure (HR = 0.30, p = .002). CONCLUSION: High preoperative preservative burden independently increases surgical failure risk in both KDB and GATT. Minimizing preservative exposure before surgery may optimize long-term minimally invasive glaucoma surgery outcomes.