IOP variations from sitting to supine postures determined by rebound tonometer

Abstract

Purpose: Postural intraocular pressure (IOP) variations have been found to be higher in glaucoma, especially in normal tension glaucoma. Higher IOP variation is also associated with greater field defects and thinner retinal nerve fiber layer. Air-puff tonometer has been found to be feasible to determine postural IOP variations. This study investigated if rebound tonometry can pick up such IOP changes. Methods: Fifty-four young adults, one eye randomly selected, had their IOP measured randomly by Pulsair EasyEye tonometer (Keeler Ltd, UK) and iCare rebound tonometer (Tiolat, Helsinki, Finland), in sitting followed by supine and finally sitting postures. IOP was measured after resting for 15 min in each posture. Masked practitioners were involved. Repeated measures analysis of variations followed by post hoc tests were used to compare the IOP findings. Postural IOP changes were measured and compared between tonometers. Results: IOP significantly varied with postures (p < 0.001). The two tonometers had similar IOP findings in each posture (p > 0.05). Rebound tonometer gave a slightly higher IOP in the first sitting posture (difference = 0.42 ± 2.23 mmHg), but provided a lower IOP in the supine posture (difference = -0.66 ± 2.58 mmHg) and the second sitting posture (difference = -0.11 ± 2.24 mmHg). Supine IOP was measured 3.10 mmHg (SD 2.35 mmHg) higher by Pulsair but only 2.02 mmHg (SD 2.18 mmHg) higher by iCare. This difference was significant (paired t-test, p < 0.01). Conclusions: Postural IOP variations were slightly lower when measured by iCare compared to Pulsair. Rebound tonometry is useful to screen for postural changes in IOP.