A Wireless Pressure Sensor for Continuous Monitoring of Intraocular Pressure in Conscious Animals

Abstract

An important aspect of eye health in humans and animal models of human diseases is intraocular pressure (IOP). IOP is typically measured by hand with a tonometer, so data are sparse and sporadic and round-the-clock variations are not well characterized. Here we present a novel system for continuous wireless IOP and temperature measurement in small animals. The system consists of a cannula implanted in the anterior chamber of the eye connected to pressure sensing electronics that can be worn by rats or implanted in larger mammals. The system can record IOP with 0.3 mmHg accuracy and negligible drift at a rate of 0.25 Hz for 1-2 months on a regulated battery or indefinitely at rates up to 250 Hz via RF energy harvesting. Chronic recordings from conscious rats showed that IOP follows a diurnal rhythm, averaging 16.5 mmHg during the day and 21.7 mmHg at night, and that the IOP rhythm lags a diurnal rhythm in body temperature by 2.1 h. IOP and body temperature fluctuations were positively correlated from moment-to-moment as well. This technology allows researchers to monitor for the first time the precise IOP history of rat eyes, a popular model for glaucoma studies.

Experimental glaucoma model with controllable intraocular pressure history

“…Since the system delivers fluid as needed to maintain the prescribed level, IOP was very stable in infused eyes. Fluctuations due to circadian rhythms 22 , ocular pulsations 23 , or other internal processes were ostensibly eliminated.…”

“…A fine polyimide cannula (ID: 0.1 mm, length: 20 mm) was passed subdermally to one eye and permanently implanted in the anterior chamber. Details of the implantation procedure have been described 22,55 In short, the cannula was heparinized overnight and filled with an artificial aqueous humor (AAH) solution (130 mM NaCl, 5 mM KCl, 5 mM NaHCO 3 , 1 mM CaCl 2 , 0.5 mM MgCl 2 , 20 mM HEPES, pH 7.25). A translimbal hole was made in the eye with a 33 G needle, and 1 μl triamcinolone acetonide www.nature.com/scientificreports www.nature.com/scientificreports/ (Triesence, Alcon, Fort Worth, TX) was injected to counteract inflammatory processes.…”

Recent Developments in Glaucoma

“…This device can only measure relative changes rather than determine absolute pressure. 31 There are currently many new intraocular sensor devices in development [32][33][34] and if any of these are proven to be accurate and safe, reliable continuous IOP monitoring for many patients may soon become a reality.…”

Optimization of orbital retraction during endoscopic transorbital approach via quantitative measurement of the intraocular pressure – [SevEN 006]

“…This can lead to visual loss. When the IOP is either momentarily too high or low, it may incur permanent damage to the optic nerve or cause retinal detachment [ 8 ]. Therefore, testing the IOP and IORP is critical in TOA surgical patients, and their accurate measurement is essential.…”