Purpose
Humans spend a large fraction of the day sleeping yet little has been published on the persistence of intraocular pressure (IOP) elevation with horizontal positioning and the effect of laterality. We performed a prospective observational study to determine IOP response to a change in body position from upright to right and left lateral decubitus positions (RLD, LLD) over 1 hr in healthy adults.
Methods
IOP was measured on 30 healthy adults using the iCare® rebound tonometer in a seated upright position. Subjects were then randomly placed in a RLD or LLD position while IOP was measured every 15 minutes for 1 hr. 20 subjects returned on a separate date and repeated the procedure on the opposite side. 26 RLD procedures and 24 LLD procedures were conducted. Statistical analysis was performed using paired, 2-tailed t-test.
Results
Average age was 31.3 yrs (SD 10.5, range 23-58). In the RLD position the IOP of the lower or dependent eye (DE) rose from a mean of 14.7 ± SD 3.3 mmHg to 17.5±3.8 mmHg at 60 min (p < 0.001), while the upper or nondependent eye (NDE) rose from a mean of 14.6±3.3 mmHg to 16.0±3.0 mmHg (p = 0.01). When placed in the LLD position the IOP of the DE rose from a mean of 14.9±2.8 mmHg to 18.9±3.3 mmHg at 60 min (p < 0.001), while the NDE rose from 15.4±3.0 mmHg to 17.4±2.8 mmHg (p < 0.001) (figs 1 and 2). In DEs, IOP peaked at 15 min for both positions then significantly decreased in the RLD position and remained stable in the LLD position. In RLD NDEs, IOP steadily rose but was not significant until 60 min. IOP elevation in LLD NDEs persisted for 30 min before significantly decreasing from the peak value. Among subjects tested in both positions, there was greater asymmetry between DEs and NDEs in the RLD position at 15 and 30 min as compared to the LLD position (p<.05). IOP elevation from baseline was significantly greater in LLD NDEs at 15 and 30 min compared to RLD NDEs (p<.05).
Conclusions
The IOP of dependent eyes increased within the first 15 min of changing from an upright to a lateral decubitus position and then remained stable or declined thereafter. NDEs behaved differently depending on laterally with IOP elevation occurring more acutely in LLD NDEs than RLD NDEs which continued to increase throughout the 1 hr period. In both positions IOP elevation was greater in DEs than ND eyes.