Non-invasive Estimation of Intracranial Pressure by Means of Retinal Venous Pulsatility

Abstract

Current techniques used to measure intracranial pressure (ICP) are invasive and require surgical procedures in order to implant pressure catheters in brain ventricles. The amplitude of central retinal vein pulsations (RVPa) has been shown to be associated with the pressure gradient between intraocular pressure (IOP) and ICP. When IOP approaches ICP, the pressure gradient drops, leading to cessation of RVPa. In this study we aim to investigate this relationship and define a new method to estimate ICP non-invasively. 10 healthy subjects (mean age 35±10) with clear medical history were included in this study. Baseline IOP was measured (Goldman tonometers) and RVP recorded using Dynamic Vessel Analyser.IOP was decreased actively using 0.5% Iopidine and RVP recorded simultaneously every 15 minutes. Digital signal processing techniques were used to measure mean RVP peak-to-peak amplitude in each cardiac cycle at different IOP levels. Linear regression equations were used to extract a relation between IOP and RVPa and to estimate the pressure at which RVPa cease (i.e. RVPa=0). At this point ICP equals IOP. IOP and ICP pressure waveforms were simulated in order to estimate ICP continuously. Results show a linear relationship between RVPa and IOP such that RVP decreases with IOP reduction. Estimated ICP ranged between 2-13.7 mmHg, all falling in the normal physiological range (i.e. 0-15 mmHg). Analysis of retinal venous pulsation in accordance with IOP may introduce a novel approach for estimation of ICP non-invasively.