Comparison of 24-Hour IOP Measurements in Sitting and Supine Positions in Glaucoma

Abstract

Purpose : To assess correlation and agreement between sitting and supine intraocular pressure (IOP) measurements in glaucoma patients and suspects as part of 24-hour IOP curve.

Methods : Measurements were performed in the sitting position using a Goldmann tonometer and in the supine position using a Perkins tonometer. IOP measurements were obtained at 7 am in the sitting position once patients arrived at the office. Patients were asked to lie down in the supine position and IOP was measured in a dark room right after at 8 am. After 60 minutes in the same conditions, IOP measurements were obtained at 9 am. After remaining hospitalized during the night, the IOP was measured in the next day upon awaking in the supine position before getting out of the bed in a dark room. The IOP measurements at 6 am, 7 am, 8 am, and 9 am were compared using a paired t-test and peak was determined when IOP>21 mmHg. Agreement between the measurements was assessed using Bland-Altman plots. Generalized estimating equations models were used to investigate the relationship between IOP measurements, taking into account the correlation between fellow eyes.

Results : The study included 138 eyes of 72 glaucoma patients and suspects. Mean age was 65.6 ± 14.4 years. Mean IOP was 16.0 ± 5.2 mmHg at 6 am, 14.0 ± 3.6 mmHg at 7 am, 14.5 ± 4.2 mmHg at 8 am, and 14.1 ± 4.2 mmHg at 9 am. IOP measurements at 6 am upon awaking in the supine position were associated with the IOP measurements at 9 am after 60 minutes in the supine position (R²=48.6%; P<0.001), 8 am in the supine position (R²=41.3%; P<0.001), and 7 am in the sitting position (R²=31.9%; P<0.001). This association was expected since measurements were closer in time. Mean differences between measurements at 6 am and those at 7 am, 8 am, and 9 am were respectively 1.9 (95% CI 1.2 to 2.7), 1.5 (95% CI 0.8 to 2.2), and 1.9 (95% CI 1.2 to 2.5) mmHg. Twenty eyes (14.5%) had peak (IOP>21 mmHg) at 6 am. Eight eyes (5.8%) had peak at 8 am and only 5 eyes (3.6%) had peak at 7 am and 9 am.

Conclusions : Despite the association, agreement among IOP measurements taken at 6 am in the supine position upon awaking in a dark room and the others measurements in the supine position was poor. Further studies assessing also night IOP measurements are needed to better understand postural effect and circadian elevation of IOP.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.