Effects of head posture on intraocular pressure and heart rate of human beings

BACKGROUND: The study analyzed the association of head posture on intraocular pressure (IOP). The study aimed to evaluate and measure the changes in IOP and heart rate (HR) of human beings on head-down posture. The study included 105 patients at the department of ophthalmology of a tertiary care center in India. SUBJECTS AND METHODS: Patients underwent applanation tonometry and HR variability (HRV) analysis before and after 20 min of head-down posture (approximately 20°). The IOP and HRV were measured. STATISTICAL ANALYSIS USED: The statistical methods of Paired t-test and linear regression analysis were applied. P < 0.05 was defined as statistically significant. RESULTS: After 20 min of the 20° head-down position, an increase in IOP was significant from 15.0 ± 2.0 mmHg to 18.0 ± 2.3 mmHg (P < 0.001). A decrease in HR was also significant from 78 ± 10.48 bpm to 72 ± 10.52 bpm after the head-down position for 20 min (P < 0.05). CONCLUSIONS: These outcomes presented the first evidence of the activation of the parasympathetic nervous system in the head-down position which might cause decreased HR and the collapse of Schlemm's canal lumen, which in turn leads to the increased IOP.