Aqueous humor uric acid and ascorbic acid concentrations and outcome of trabeculectomy

Objective: To determine if there is an association between the surgical outcome of trabeculectomy and uric acid and ascorbic acid concentrations in the aqueous humor at the time of the procedure. Patients, Materials, and Methods: Aqueous humor samples were collected from the eyes of 169 of 249 adult patients who underwent trabeculectomy alone for any type of glaucoma between April 1989 and July 1995. Postoperatively, all medical records were reviewed and outcomes were classified as successful, unsuccessful, or indeterminate. The ascorbic acid and uric acid concentrations were determined in masked fashion by high-pressure liquid chromatography. Factors associated with surgical outcome were determined. Results: Uric acid concentration was higher in unsuccessful eyes (mean±SD, 0.21±0.08 mmol/L, n=26) than in successful eyes (0.15±0.09 mmol/L, n=91, 95% confidence interval for difference, 0.02-0.10 mmol/L). Ascorbic acid levels were not significantly different in the eyes with unsuccessful (1129.9±601.9 μmol/L) and successful (1334.3±511.0 μmol/L) surgery (95% confidence interval for difference, -475.2 to 66.4 μmol/L, P=.13) surgery. Other factors associated with failure were previous surgery and surgery performed at the inferior limbus. A multiple polytomous logistic regression analysis was performed, after excluding the small number of operations performed at the inferior limbus. The odds ratio for failure increased by a factor of 1.68 for every 1- mmol/L increase in uric acid (95% confidence interval, 1.16-2.43, P=.006). Conclusions: Uric acid levels were higher at the time of surgery in eyes that had unsuccessful outcomes than in those with successful outcomes. No significant difference in ascorbic acid levels was detectable. A higher uric acid level in the aqueous humor is a risk factor for trabeculectomy failure and might be tested as a prognostic indicator. Understanding the host characteristics that determine whether a trabeculectomy will be successful in a given eye is important. Data from the Fluorouracil Filtering Surgery Study Group suggest that in eyes with previous surgery the following are risk factors for surgical failure: time elapsed since the last procedure involving a conjunctival incision, the number of previous procedures involving conjunctival incisions, high preoperative intraocular pressure, and Hispanic ethnicity. In addition, previous intraocular surgery itself, age, race, and the diagnosis of uveitic or neovascular glaucoma are generally considered risk factors for trabeculectomy failure.