Objective: To investigate the position-related changes of anterior chamber angle anatomy in normal eyes and shallow anterior chamber eyes. Methods: A prospective study was conducted. Sixty-four eyes from 64 patients were divided into two groups by peripheral anterior chamber depth: the normal group(>1/3CT) and the shallow anterior chamber group(≤1/3CT). The anterior chamber angles of the eyes were measured in supine and sitting positions by ultrasound biomicroscopy (UBM) with balloon technology (superior

inferior

nasal and temporal quadrants). Statistical analysis was used to evaluate positional changes in AA

AOD500. Anterior chamber depth、lens thickness and axial length were obtained by optical biometer IOLMaster 700. Results: In both two groups

the angle anatomy was narrower superiorly (P<0.001) and wider inferiorly (P<0.001) in the sitting position

but no positional differences in nasal or temporal angle anatomy were observed (P>0.05). The superior positional differences of the shallow anterior chamber group were greater than those of the normal group (P=0.048;P=0.046). The inferior positional differences of the shallow anterior chamber group were wider than those of the normal group (P=0.044;P=0.031).The lens thickness of the shallow anterior chamber group was significantly thinner than that of the normal group (P<0.001). Conclusion: The angle anatomy was affected by different exam position. Both the relaxation of zonule and the gravity play an important role in the positional differences of the angle anatomy. The angle anatomy was narrower superiorly and wider inferiorly while the subject was sitting in both two groups

but the positional differences of the shallow anterior chamber group were greater than those of the normal group. In the clinical diagnosis

more attention should be paid to the positional effect of the patients with shallow anterior chamber in angle anatomy examination.