Effect of Supine Position on Episcleral Venous Pressure in Normal Human Eyes using a Portable Electronic Episcleral Venomanometer

Abstract

Purpose : It has been shown that intraocular pressure (IOP) changes with body position, but the mechanism is not well understood. In this study, we evaluated changes in episcleral venous pressure (EVP) between seated and supine positions and compared with changes in IOP and blood pressure in normal subjects.

Methods : Twenty eyes from 10 normal subjects (all females; 30 ± 7 years, mean ± SD) were included in the study. Blood pressure, pulse rate, IOP, and EVP of both eyes were first measured in the seated position. Thirty minutes later and after being in the supine position for 5 minutes, the same measurements were repeated. Systolic and diastolic blood pressures (SBP and DBP), and pulse rate (PR) were determined by a digital monitor. IOP was measured by pneumatonometry. EVP was assessed in a selected episcleral vein by using a computer-controlled portable electronic episcleral venomanometer with video recording and image processing to determine the pressure required to initiate collapse of the vein. Changes in IOP, EVP, systolic and diastolic blood pressures, and pulse rate between 2 body positions and correlations between changes in those variables were analyzed by using generalized estimating equation models and regression analysis, respectively.

Results : Mean IOP increased from 15.5 ± 2.0 mmHg in the seated position to 19.5 ± 2.2 mmHg in the supine position (P< 0.001, Table 1) but the change in EVP was smaller in magnitude (from 6.0 ± 1.0 mmHg to 6.9 ± 0.9 mmHg, P< 0.001, Table 1). DBP and PR but not SBP were lower in the supine position (Table 1). The change in EVP was not correlated with the change in IOP but showed moderate correlations with blood pressure changes (Table 2). Also, there were no significant correlations between IOP change and BP and PR changes (Table 2).

Conclusions : Both IOP and EVP are higher in the supine position compared to the seated position, but the magnitude of changes is not the same. EVP change is more strongly correlated with blood pressure change than IOP change. Future studies are required to identify the other contributing factors of postural IOP change.

This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.

 

Table 1. Comparison of IOP, EVP, Blood Pressure and Pulse Rate between Seated and Supine Positions

 

Table 2. Correlations between Changes in IOP, EVP, BP, and PR from Seated to Supine Position