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 μm 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 μm 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.