BACKGROUND: To assess the characteristics of the ciliary sulcus in patients with myopia with different axial lengths using ultrasound biomicroscopy (UBM). METHODS：: A total of 108 eyes from 54 patients were recruited between January and March 2024. Patients were matched for age, cylinder and white-to-white (WTW) ratio, and further divided into a control axial length (AL) group (CON, AL <
26.5mm, 54 eyes) and a long AL group (L-AL, AL ≥ 26.5mm, 54 eyes). Anterior and posterior chamber parameters were examined based on UBM. Anterior chamber parameters included sulcus-to-sulcus distance (STS) in the horizontal and vertical orientation, lens anterior surface to ciliary sulcus distance (STSL), anterior segment length (ASL) and anterior chamber depth (ACD). Posterior chamber parameters included ciliary process length (CPL), trabecular-ciliary process distance, trabecular-ciliary angle (TCA), iris-ciliary angle (ICA) and maximum ciliary body thickness in four spatial directions. RESULTS: The anterior chamber parameters, including STS, STSL and ASL, were significantly lower in the horizontal direction than those in the vertical direction in both groups, whereas STS was significantly lower in the CON group than in the L-AL group. Posterior chamber parameters, including CPL, TCA and ICA, showed significant spatial differences between the two groups. Furthermore, STSL correlated significantly with ACD, mean keratometry and WTW. CONCLUSIONS: Significant spatial differences in ciliary sulcus and ciliary body morphology were observed in patients with axial myopia. In ICL size selection and vault prediction, STS and STSL are potential indicators in preoperative ICL assessment.