Although glaucoma is a multifactorial disease, elevated intraocular pressure (IOP) remains the most important known risk factor. Different systemic and local factors are thought to influence an individual's IOP. There can be a clinically significant rise in IOP when going from upright to horizontal or inverted body positions. Although there is a significant interindividual variability, the magnitude of the IOP change is greater in glaucomatous eyes. As patients usually spend a significant portion of their lives in the horizontal position, mainly during sleep, this is highly relevant. In this review we discuss the relationship between postural changes and IOP fluctuation, including changes in both body and head position. The possible mechanisms involved and the main implications for glaucomatous eyes are discussed. Finally, considerations with regard to sleep position in glaucoma patients are made based on evidence in the literature.
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