Membrane formation in the chamber angle after failure of argon laser trabeculoplasty: Analysis of risk factors

Abstract

Aim - Membrane formation in the chamber angle induced by argon laser trabeculoplasty (ALT) can be a cause of treatment failure. Identification of risk factors for membrane formation was the primary aim of this retrospective study. Methods - Semithin sections of trabeculectomy specimens obtained in a 2 year period were examined by light microscopy. 122 eyes which were treated with one or more ALTs before trabeculectomy were identified. In 46 eyes, a sufficient amount of trabecular meshwork was obtained to permit morphological analysis. Results - Eyes treated with ALT had a significantly higher incidence of membrane formation (p = 0.001). In 23/46 specimens a cellular and collagenous membrane was observed covering the entire trabecular meshwork. In 14/23 specimens (61%), this membrane was readily visible at low power magnification (x 40). Comparison of these eyes with those without membrane formation revealed a significant difference in the number of ALTs (mean 2.07 (SD 0.73) v 1.48 (0.59); p = 0.026) and in preoperative IOP (32.0 (9.7) v 26.2 (8.4) mmHg; p = 0.04). Conclusions - Membrane formation in the chamber angle is a frequent cause of ALT failure. The major risk factor is the number of ALTs performed.