Methods: Fellow eyes with unilateral APAC and one random select eye of PACS were evaluated by ultrasound biomicroscopy (UBM). Anterior chamber depth (ACD), angle opening distance (AOD500/AOD750),lens thickness (LT), angle recess area (ARA500/ARA750), trabecular ciliary process distance (TCPD500/TCPD750) in the superior, inferior, nasal and temple quadrants were measured between the 2 groups.

Results: 46 subjects with unilateral APAC and 103 PACS subjects were included. Significant differences (P<0.001) were found between APAC fellow eyes and PACS eyes in ACD, AOD500, LT, AOD750, ARA500, ARA750. TCPD500 and TCPD750 were not statistically significant between 2 groups.

Conclusions: APAC fellow eyes have thicker lens, shallower ACD and crowded anterior chamber angle than PACS. PACS with anatomic characteristics as fellow eye of APAC are at greater risk for developing primary angle closure.