In which position is intraocular pressure (IOP) typically higher, standing or laying down?

Intraocular pressure (IOP) is typically higher when a person is laying down compared to standing. This phenomenon can be attributed to several physiological factors. When an individual is in a horizontal position, venous return to the heart increases, which can lead to increased central venous pressure. This, in turn, affects the drainage of aqueous humor through the trabecular meshwork and Schlemm’s canal. In a supine position, the hydrostatic pressures in the eye are altered, which may restrict the outflow of aqueous humor and result in elevated IOP.

Moreover, gravitational factors play a role. When standing, the gravitational pull helps in fluid drainage, whereas, in a horizontal position, this drainage is less efficient. Additionally, studies have shown that IOP measurements taken in a supine position can be higher due to these changes in hemodynamics and fluid dynamics.

Thus, the understanding that IOP is generally higher when laying down is crucial for clinical assessments and interpreting IOP readings based on patient positioning.