Intraocular Pressure and Intracranial Pressure Measurement with Continuous Wireless Telemetry to Quantify Translaminar Pressure Difference in Nonhuman Primates

Abstract

Purpose : Recent retrospective clinical studies and animal experiments have suggested that cerebrospinal fluid pressure (CSFP) is important in glaucoma pathogenesis. Intraocular pressure (IOP) and CSFP are the driving components of translaminar pressure difference (TLPD), which directly effects the optic nerve head and contained lamina cribrosa. The lack of continuous and accurate CSFP measurement has impeded research into the roles of TLPD in glaucoma.

Methods : We have developed an implantable pressure telemetry system based on a small piezoelectric sensor with low drift. For these studies, we measure physiologic pressures in awake and behaving nonhuman primates (NHPs) over 22 consecutive days at 200Hz for 15 seconds every 2-1/2 minutes, 24 hours per day. Unilateral IOP is measured from the anterior chamber, intracranial pressure (ICP) is measured from the brain parenchyma (as a surrogate measure of CSFP), and arterial blood pressure (BP) is measured from the lumen of the carotid artery.

Results : Data were collected in one male rhesus macaque (Figure 1) over 22 consecutive days, and TLPD was quantified in real time as IOP-ICP. Hourly means of IOP, ICP, and TLPD were plotted (Figure 1). Results show that mean ICP is higher during sleep in NHPs (Figure 1), resulting in lower nocturnal TLPD. ICP displays a nycthemeral rhythm in spite of the fact that NHPs sleep sitting up with the neck flexed. While the NHP is asleep and the neck flexed, ICP is significantly higher (p-value < 0.001) than when the NHP is awake and active with the head upright. As expected, IOP did not show the nocturnal elevation typically associated with supine position in human sleep.

Conclusions : TLPD was significantly increased during waking hours in this animal. These preliminary data show the potential of this telemetry system in investigating glaucoma pathogenesis and progression in a NHP model of unilateral glaucoma and/or ICP lowering.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.

 

Figure 1. (Top) Fifteen seconds of raw, uncalibrated continuous carotid BP, IOP and ICP from one male rhesus macaque. (Bottom) Hourly mean±SD of IOP (green), ICP (red), and TLPD (black) over 22 consecutive days.