Background: Laser peripheral iridotomy is a useful method in primary angle-closure eyes to prevent angle-closure attack and development of glaucomatous optic nerve damage. The aim of this study was to quantify morphological changes after LPI and their impact on intraocular pressure, and to evaluate predictive parameters for enlarging the anterior chamber angle after laser peripheral iridotomy.

Methods: Ultrasound biomicroscopy images and intraocular pressure before and after laser peripheral iridotomy from 62 eyes of 34 patients with primary angle-closure were retrospectively analysed. Anterior chamber angle, anterior chamber depth, lens thickness, iris curvature and a newly defined parameter, the end-iris-lens vault were measured.

Results: In each quadrant anterior chamber angle was on average significantly larger (at 12 o'clock: from 10.1° to 15.0°; at 3 o'clock: from 13.4° to 19.8°; at 6 o'clock: from 12.2° to 18.5°; at 9 o'clock: from 12.9 to 17.9°; p<0.001) and iris curvature significantly smaller (at 12 o'clock: from 0.26 mm to 0.10 mm; at 3 o'clock: from 0.21 mm to 0.08 mm; at 6 o'clock: from 0.25 mm to 0.08 mm; at 9 o'clock: from 0.21 mm to 0.08 mm; p<0.001) after laser peripheral iridotomy. Anterior chamber depth, lens thickness and end-iris-lens-vault did not significantly change. Anterior chamber angle in each quadrant (p<0.05), and iris curvature at 3 and 6 o'clock positions (p<0.05) were highly predictive for the enlargement of the anterior chamber angle after laser peripheral iridotomy. Intraocular pressure was slightly lower after laser peripheral iridotomy (from 16.6 mmHg to 16.1 mmHg).

Conclusions: In primary angle-closure eyes, laser peripheral iridotomy enlarges the angle and flattens the iris significantly. This study demonstrated that a small anterior chamber angle and a large iris curvature are predictive parameters for a greater enlargement of the anterior chamber angle after laser peripheral iridotomy. These new findings underline the importance of the ultrasound biomicroscopy and may help in counselling patients about laser peripheral iridotomy.