Effect of Head and Body Position on Intraocular Pressure

Objective: To investigate the effect of different head and body positions on intraocular pressure (IOP) in a randomized study. Design: Prospective, comparative case series. Participants: Twenty-four healthy volunteers. Methods: Subjects had 2 sets of IOP measurements performed, sitting and recumbent, with the order of these sets of measurements randomized. In the sitting position, IOP was measured in neutral neck position, neck extension, and neck flexion, with the order of measurements randomized. In the recumbent positions, IOP was measured in the supine position, and right and left lateral decubitus positions, with the order of measurements also randomized. All IOP measurements were performed with pneumatonometry. Results: Mean IOP of right and left eyes while sitting with the neck in neutral position was 14.8 +/- 2.0 mmHg, which was significantly lower than IOP measured with neck flexion or extension or in the recumbent positions. As well, IOP in neck flexion was significantly higher than IOP in neck extension (all P<0.0001). The IOP was higher in the dependent eye when measured in the right lateral decubitus position (18.8 +/- 2.9 vs 17.7 +/- 3.1 mmHg; P = 0.016), but did not attain significance in the left lateral decubitus position (P = 0.076). Conclusions: In normal subjects, IOP is lowest when measured while sitting with the neck in the neutral position. All other head and body positions result in an elevation of IOP compared with the position used for typical clinical measurements. Lateral decubitus positions may result in a small increase in the IOP in the lower eye. Further research is required to determine whether similar elevations of IOP occur in glaucoma patients, and elucidate the clinical significance of these elevations.