Increasing the size of a small peripheral iridotomy widens the anterior chamber angle: an ultrasound biomicroscopy study

PURPOSE: A peripheral iridotomy (PI) is the treatment of choice for pupillary block. In this study we investigated the effect of enlarging the size of a small PI on the anterior chamber angle in patients with angle closure using ultrasound biomicroscopy (UBM). PATIENTS AND METHODS: Patients who had been treated with laser peripheral iridotomy for angle closure and were identified to have a small patent PI (<100 microm) with still appositionally closed anterior chamber angle were selected prospectively. The anterior chamber angle was assessed using UBM. The angle opening distance 500 microm from the scleral spur (AOD500) as well as the anterior and posterior chamber depth (ACD and PCD) 1000 microm from the scleral spur was measured. In addition, the ACD/PCD ratio was calculated. Afterwards, the PI was enlarged using an Nd: YAG laser and the UBM measurements were repeated as described above. RESULTS: Six eyes of six patients were examined. After the enlargement of the PI the average AOD500 increased from 109 microm (+/- 36) to 147 microm (+/- 40) (p <0.05). The ACD/PCD ratio increased from 0.36 (+/- 0.065) to 0.67 (+/- 0.185) (p <0.05). CONCLUSION: Patients with a small PI and appositionally closed anterior chamber angle should have a repeated laser treatment. The ACD/PCD ratio, measured 1000 microm from the sclerl spur, is a new method to describe the features and changes of the anterior chamber angle taking into account the configuration of the iris and the posterior chamber depth.