This study aims to detect whether the optic nerve sheath diameter (ONSD) can be used to dynamically monitor intracranial pressure (ICP). Adult patients undergoing invasive ICP monitoring on the day of admission are included in this study. For each patient, the ONSD is first measured in the supine position and then in the 30{}^{\circ } head-up position. Subsequently, a dynamic test is conducted on 16 patients. The ONSD is measured in the supine position once a day for three consecutive days starting on the day of admission. There is a strong correlation between the ONSD and ICP values in the supine position on admission (r = 0.799), and when patients are changed from the supine to the 30{}^{\circ } head-up position, the ICP and ONSD values decrease correspondingly. However, the change in ICP is not strongly correlated with the change in ONSD (r = 0.358). In the dynamic test, a good agreement between the ICP and ONSD only exists in three patients (18.8%), and three patients have completely different profiles for ICP and ONSD. These results suggest that the changes in the ONSD and ICP values are not closely correlated after dynamic observation. Therefore, measurement of the ONSD may not be a suitable tool to dynamically monitor ICP.