Intraocular Pressure Measurements in Standing, Sitting, Prone, and Supine Positions

In this study, intraocular pressure (IOP) was measured in sitting, supine, prone, and standing (ST) positions and again five minutes after standing (ST-5) utilizing a Tono-Pen AVIA in 124 eyes of 62 healthy subjects with ages ranging from 21 to 59 years (mean 30 +/- 10 years). In each subject, the average IOP of both eyes was used for the statistical evaluation. The mean IOP difference between the ST and sitting positions was -0.13 +/- 1.63 mmHg (p = 0.548); between ST-5 and sitting, it was 0.53 +/- 1.24 mmHg (p = 0.001); between supine and sitting, it was 1.30 +/- 1.48 mmHg (p < 0.001); between ST and supine, it was -1.43 +/- 1.74 mmHg (p < 0.001); between ST-5 and supine, it was -0.77 +/- 1.59 mmHg (p < 0.001); between prone and supine, it was 2.24 +/- 1.92 mmHg (p < 0.001); between ST and ST-5, it was -0.67 +/- 1.84 mmHg (range: -7.5 to 5 mmHg) (p = 0.007); between prone and ST, it was 3.46 +/- 2.01 mmHg (p < 0.001); between ST-5 and prone, it was -2.46 +/- 1.67 mmHg (p < 0.001); and between sitting and prone, it was -3.22 +/- 1.56 mmHg (p < 0.001). The results show a significant IOP increase in the ST-5 position, suggesting that such measurements need to be performed in an attempt to explain the progression of glaucoma in apparently normal-tension patients.