The effects of different energy levels in argon laser trabeculoplasty

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

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 (x40). 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) mm Hg; 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.

Two-year follow-up of intra-ocular pressure control with long duration argon laser trabeculoplasty

The two-year results of intra-ocular pressure control in the first prospective study of standard (0.1 second) and long (0.2 second) duration argon laser trabeculoplasty are presented. The two groups were comparable for intra-ocular pressures and treatment scores at the start of the study. An early benefit in intra-ocular pressure reduction was found for 0.2 second trabeculoplasty in the first year, which disappeared during the second-ond year of follow-up. No reduction in medications occurred following laser trabeculoplasty. There was no difference in the frequency of further interventions (repeat trabeculoplasty or drainage surgery) between the two groups. There was a strong correlation between the intra-ocular pressures of the first and second treated eyes. No clinical benefit was demonstrated for the longer duration over standard argon laser trabeculoplasty.

Standard and long duration repeat argon laser trabeculoplasty

A retrospective survey was performed on 22 patients with chronic simple glaucoma who had undergone a single repetition of argon laser trabeculoplasty. Two groups were identified who had received treatment with either 0.1 or 0.2 sec duration. The 0.2 sec group showed a reduction in the medications used, in addition to a comparable fall in intra-ocular pressure to the 0.1 sec group, and had a lower rate of drainage surgery. These findings may have arisen because of the higher energy delivered as a result of the longer duration employed. However, there are risks of repeating argon laser trabeculoplasty: one patient in the 0.2 sec group developed a rise in intra-ocular pressure of 15 mmHg following the repeat treatment, and required drainage surgery one month later.

Argon laser trabeculoplasty with standard and long duration

A prospective study of 0.1 sec and 0.2 sec duration argon laser trabeculoplasty was undertaken in 33 patients with chronic simple glaucoma. Patients were randomly allocated to receive 0.1 sec trabeculoplasty to the eye and 0.2 sec trabeculoplasty to the other. No difference was found in the fall in intra-ocular pressure or in glaucoma control between the two durations over the six months of the study. However, 0.2 sec argon laser trabeculoplasty was reported to be more uncomfortable of 60% of patients.