A Comparison Of Intraocular Pressure Measurements Using Tono-Pen Avia And Icare Pro Tonometers In Standing, Sitting, And Supine Positions

Intraocular pressure (IOP) fluctuations throughout the day, due to circadian rhythms and body position, can influence glaucoma progression. The aim of this study is to assess the IOP variations using two distinct devices, namely Icare Pro (ICP) and Tono-Pen Avia (TPA), and to investigate the effects of standing, sitting, and supine positions on IOP.

This prospective case series involved a comparison of IOP measurements obtained between 10 am and 12 pm by two different observers, who were not aware of the results obtained from the other, using ICP and TPA devices in 64 eyes of 32 healthy individuals, with IOP being measured in sitting, supine, prone, and standing (standing 1) positions, as well as five minutes after standing (standing 2). Patients with systemic and ocular diseases, any inability to fixate on the target, with smoking history and an alcohol addiction were excluded from the study. Statistical analysis was conducted using a paired t-test and Pearson's correlation coefficient.

Both ICP and TPA devices showed a statistically significant increase in IOP measurements in the supine and standing 2 positions (p < 0.05), compared to the sitting position. The mean IOP difference between the two devices was 0.57 ± 2.10 mmHg (range: −3.80 to 6.60 mmHg) in the sitting position (p < 0.05), 0.93 ± 2.49 mmHg (range: −4.50 to 7.10 mmHg) in the supine position (p < 0.05), 0.37 ± 1.96 mmHg (range: −5.20 to 5.00 mmHg) in the standing 1 position (p = 0.102), and 0.73 ± 2.03 mmHg (range: −4.5 to 6.4 mmHg) in the standing 2 position (p < 0.001).

The findings of this study indicate that both TPA and ICP devices showed an increase in IOP in the supine position, as well as in the standing 2 position. It is interesting to note that, switching from supine to standing 1, a significant decrease in IOP (p < 0.001) was found, although such a decrease was not significant when compared to the sitting one with the TPA (p = 0.187). Lastly, after 5 min standing, the IOP became higher than in the sitting position (p < 0.05) with both instruments. Therefore, these measurements should be performed in patients with glaucoma, as it may help to explain disease progression in individuals with apparently normal tension or in those who are compensated and suggest right medical or surgical procedures.