Narrow angles and angle closure: anatomic reasons for earlier closure of the superior portion of the iridocorneal angle.

OBJECTIVE To quantitatively investigate the ultrasound biomicroscopic features of eyes with asymmetric narrowing of the iridocorneal angles. METHODS Asymmetric angles were defined as those differing by 2 or more Shaffer grades between the superior and inferior angles. We performed ultrasound biomicroscopy on 18 eyes in 18 patients. Measurements of the following were made: the angle recess area, the triangular area bordered by the anterior iris surface, the corneal endothelium, and a line drawn from 750 microm anterior to the scleral spur; the y-intercept, the estimated angle opening distance at the level of the scleral spur; acceleration, which describes how rapidly the angle widens from the iris root; trabecular-ciliary process distance, the distance between the trabecular meshwork and the ciliary body at 500 microm anterior to the scleral spur; and angle recess-iris insertion distance, the distance between the apex of the angle recess and the iris insertion on the ciliary body face. RESULTS In the superior angle, 11 eyes developed appositional closure, 10 with B-type (apposition beginning at the iris root) and 1 with S-type (apposition beginning at the line of Schwalbe). Four eyes also had apposition inferiorly (1 B-type and 3 S-types). The y-intercept, angle recess areas, trabecular-ciliary process distance, and angle recess-iris insertion distance were significantly smaller in the superior quadrant. S-type angles predominated in the inferior angle, and B-type angles did in the superior angle, indicating a more posterior insertion of the iris in the wider inferior angles. CONCLUSIONS Asymmetry in eyes with narrow angles occurs because of differences in iris insertion position on the ciliary body face and from asymmetry of the ciliary body position.