To compare directly the results of 4 tonometers in measuring postural change in the intraocular pressure (IOP) between sitting and lying body positions.
In 19 healthy subjects, the IOP was measured both eyes with a Goldmann applanation tonometer (GAT) while sitting, then using the same GAT with the subject in the left lateral decubitus position after lying for 15 minutes, using a novel system comprising a motorized bed and a modified slit-lamp table. On the next day, the sitting IOP was measured in 1 eye using GAT, and additionally in random order Tonopen XL and pneumatonometer. Then subjects were asked to lie down, and the IOP was measured with these tonometers and also with a hand-held applanation tonometer (HA-2) after lying for 15 minutes and for 45 minutes; measurements were made with subjects in the supine position except with GAT.
There were 10 male and 9 female subjects, with a mean age of 33.0±12.4 years. On day 1, the sitting GAT IOP (mm Hg) was 13.7±3.0 right eye and 13.6±2.8 left eye (P=0.7) and the lying GAT IOP was 17.8±3.5 right eye and 18.1±3.2 left eye (P=0.3 for inter-eye postural IOP change). Postural change in the right and the left eyes was moderately correlated, with a coefficient of 0.453. On day 2, postural changes after lying for 15 minutes as measured with a GAT, a Tonopen, a pneumatonometer, and a HA-2 were 4.9±2.6, 1.6±1.8, 4.2±2.0, and 3.1±2.7, respectively. After lying for 45 minutes, it decreased to 3.3±2.1, 1.1±4.3, 3.1±2.5, and 2.6±3.3, respectively; this IOP decrease was statistically significant for the GAT and the pneumatonometer. The inter-subject variability was large, as in some subjects there was nearly no postural change in the IOP, whereas in some the IOP increased by 8 to 10 mm Hg. Ninety-five percent limits of agreement showed a poor agreement between GAT and the other 3 tonometers in the sitting and lying IOPs and postural IOP changes measured.
The average postural IOP change was similar when measured with GAT and a pneumatonometer, smaller with a hand-held GAT, and much smaller with a Tonopen XL. This change decreased significantly when lying between the 15- and 45-minute time points. The inter-subject variability in postural IOP was remarkable, consistent with previous reports, suggesting the importance of this parameter in clinical glaucoma practice. Inter-device agreement was poor and similar to previous reports.