BACKGROUND This study aims to investigate the pattern of intraocular pressure (IOP) changes in different postures among patients with open-angle glaucoma (OAG). METHODS A observational study was conducted on a total of 74 patients with OAG (148 eyes). IOP measurements were taken in a variety of positions, including supine, left lateral decubitus, right lateral decubitus, head tilted downwards position with immediate head-up (transient head tilted downwards), seated, seated with head tilted downwards, standing, and walking. Each position was held for 5 min before measurement. In all positions, the patient maintains both eyes looking forward and remains alert. In the head tilted downwards position, the angle of head tilt with respect to the sagittal plane was 30°. RESULTS The overall trend of IOP changes showed a significant decrease with an increase in the position height (r = 0.037, p < 0.001). The IOP was significantly higher in the supine, left lateral decubitus, right lateral decubitus, and head tilted downwards positions than in the seated position (p < 0.001). Compared with the seated position with eyes at primary gaze, IOP decreased significantly when standing (p = 0.008) or walking (p < 0.001). The IOP in the left lateral decubitus and right lateral decubitus was significantly higher than in the supine position (p = 0.008, p = 0.001, respectively). The IOP decreased significantly during walking compared with standing (p < 0.001). CONCLUSIONS The magnitude of IOP strongly correlates with the body position during IOP measurement. The head tilted downwards, supine, left lateral decubitus, and right lateral decubitus positions result in a higher IOP than IOP at the seated position. Patients with OAG can potentially reduce IOP fluctuations by adjusting their daily postures.