Intraocular Pressure Measurements in Standing, Sitting, and Supine Position: Comparison between Tono-Pen Avia and Icare Pro Tonometers

Background: Intraocular pressure (IOP) is influenced by body position. The purpose of this study is to compare the IOP measurements obtained with two different devices, to investigate IOP changes in standing, sitting, and supine positions. Methods: In this comparative prospective case series, IOP was measured in sitting, supine, prone, and standing (standing 1) positions and again five minutes after standing (standing 2), utilizing an Icare Pro (ICP) and a Tono-Pen Avia (TPA) in the 64 eyes of 32 healthy subjects. Results: Compared to the sitting position, both devices showed an increase in the IOP both in supine and standing 2 positions (p < 0.05). The mean IOP difference between the two devices was: in the sitting position, 0.57 +/- 2.10 mmHg (range: -3.80 to 6.60 mmHg) (p < 0.05), in the supine position, 0.93 +/- 2.49 mmHg (range: -4.50 to 7.10 mmHg) (p < 0.05), in the standing 1 position, 0.37 +/- 1.96 mmHg (range: -5.20 to 5.00 mmHg) (p = 0.102), and in the standing 2 position 0.73 +/- 2.03 mmHg (range: -4.5 to 6.4 mmHg) (p < 0.001). Conclusions: The results highlight an agreement between the TPA and ICP, both confirming not only the increase in IOP in the supine position, but also showing an increase in the standing 2 position. Therefore, it is suggested to perform such measurements in patients with glaucoma, to explain its progression in an apparently normal tension or in compensated patients.