Rebound tonometer has been used to measure the intraocular pressure (IOP) in the supine as well as normal upright positions. We investigated the reliability of IOP measurements using the rebound tonometer in the upright and supine positions.

IOP was measured in 30 patients (60 eyes) with open-angle glaucoma who had no history of ocular surgery and no anterior segment pathology, in both the upright and supine positions using rebound tonometer (IcarePRO; Icare Finland Oy, Finland). The average IOP value after 6 measurements was recorded. We measured IOP repeatedly until 3 reliable values within normal limits of the measurement's variation were obtained. We calculated the intraclass correlation coefficient (ICC), coefficient of variation, and number of repeated measurements necessary to obtain 3 reliable IOP values in each position as measured by one examiner.

ICC values for IOP measurements were 0.852 (95% confidence interval [CI], 0.784-0.903; p < 0.001) in the upright position and 0.684 (95% CI, 0.563-0.784; p < 0.027) in the supine position. Coefficient of variation was 8.7 ± 0.1% in the upright position and 24.0 ± 0.1% in the supine position. An average of 3.3 times of repeated measurements in the upright position and 6.2 times in the supine position were necessary to obtain 3 reliable IOP values within the normal range of standard deviation.

When measuring IOP using the IcarePRO rebound tonometer, the measurement reliability was different between the upright and supine positions. Reproducibility of IOP measurements was lower in the upright than the supine position.