Argon Laser Trabeculoplasty (ALT): Predictors of Failure
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PURPOSE. ALT is widely used to control intraocular pressure (IOP) in glaucoma. We wished to determine predictive factors for long term success of ALT performed by supervised residents in training on patients at a local VA Hospital in Dallas. METHODS. Charts of patients with primary open angle glaucoma who underwent ALT between 2001 and 2011 were reviewed retrospectively. Those with follow up < 3 months, prior ALT/SLT, filtering procedure or inadequate data were excluded. The dependent variable was time to failure after ALT. Failure was defined as any additional medication, ALT/SLT or glaucoma filtering surgery. All patients were treated with 360 ° ALT. Logistic regression and receiver operating characteristic (ROC) analysis was performed to assess correlation between time to failure after ALT and age, pre-op IOP, C/D ratio, visual field defect, family history, refractive error, hypertension, diabetes, number of medications, laser energy used, central corneal thickness. RESULTS. Evaluable data was obtained on 206 patients; mean age 65, 98% male, and 61% black. 40.8% (84/206) were classified as ALT failures. Failure and non-failure patients had equal follow-up duration of median 2 yr. Pre-ALT LogMar (mean (SD) 0.25 (.3) vs. 0.35 (.3)), no. of glaucoma medications (2.9 (1.0) vs. 3.3 (1.0)), and myopia (46% vs. 61%) differed, respectively, between ALT failures and non-failures (p<0.05). In multivariable logistic regression models, after adjusting for age, hypertension, and diabetes, we found that myopia was protective (odds ratio (OR) =0.39, 95% CI 0.21-0.78, p=0.005) but that higher laser energy ((OR=1.6 for a 20k increase in energy, 95% CI: 1.1-2.4, p=0.005) was associated with increased risk associated for ALT failure; model ROC AUC = 0.70 (95% CI: 0.63-0.78). DISCUSSION. Our VA patients were mainly males but had good ethnical diversity. Better response in myopia may be related to thickness of trabecular meshwork while poorer response to increased laser energy may be from thermal damage. Patients using more than three meds were on systemic carbonic anhydrase inhibitors CONCLUSIONS. ALT results were better in patients who used more than 3 meds, were myopic and required less laser energy.