AIM: To study the relationship between ultrasound biomicroscopy (UBM) and Lenstar when measuring anterior chamber depth (ACD) in eyes with shallow anterior chamber, and the necessity of conducting both examinations. METHODS: This is a retrospective observational study including 56 acute primary angle closure (APAC) eyes and 47 primary angle closure suspect (PACS) eyes with shallow ACD. ACD value measured by Lenstar and UBM were documented. The Bland-Altman plots were examined separately in all included eyes, APAC eyes and PACS eyes, for the assessment of agreement between two measurements. The agreement was compared across different population by evaluating mean difference, width of 95% limit of agreement (LoA) and the presence of proportional bias or outliers in Bland-Altman plots. RESULTS: The average ACD in APAC eyes (1.71±0.23 mm) was significantly smaller than that in PACS eyes (1.79±0.25 mm, P=0.038). Bland-Altman plots of both APAC eyes and PACS eyes showed small mean difference without the presence of proportional bias. However, compared with PACS eyes, the Bland-Altman plot of APAC eyes had wider 95% LoA and more outliers outside the 95% LoA. CONCLUSION: Despite the small ACD values, the two methods in measuring ACD, Lenstar and UBM, demonstrate substantial consistency when measuring PACS eyes. However, for the APAC population, the agreement might be limited, and thus the measured values should be interpreted with caution.