A Circadian and Cardiac Intraocular Pressure Sensor for Smart Implantable Lens

Abstract

This paper presents a new system to measure the Intraocular Pressure (IOP) with very high accuracy (0.036 mbar) used for monitoring glaucoma. The system not only monitors the daily variation of the IOP (circadian IOP), but also allows to perform an spectral analysis of the pressure signal generated by the heartbeat (cardiac IOP). The system comprises a piezoresistive pressure sensor, an application-specific integrated circuit (ASIC) to read out the sensor data and an external reader installed on customized glasses. The ASIC readout electronics combines chopping modulation with correlated double sampling (CDS) in order to eliminate both the amplifier offset and the chopper ripple at the sampling frequency. In addition, programmable current sources are used to compensate for the atmospheric pressure ( 800-1200 mbar ) and the circadian component (± 7 mbar) thus allowing to read out the very weak cardiac signals (± 1.6 mbar) with a maximum accuracy of 0.036 mbar.

An Energy-Efficient 3.7-nV/<inline-formula> <tex-math notation="LaTeX">$\surd$ </tex-math> </inline-formula>Hz Bridge Readout IC With a Stable Bridge Offset Compensation Scheme

“…To avoid this problem, bridge offset should be compensated before amplification. This can be done by using: 1) an external offset compensation network to trim the bridge [19] and 2) a current DAC to inject a programmable current into the bridge [20]. However, the bridge and the compensation circuitry will inevitably have different temperature dependencies, leading to significant temperature drift.…”

A Power-Efficient Readout for Wheatstone-Bridge Sensors With COTS Components

“…However, in practice, the frequency components in the TIA outputs that are greater than half the sampling rate will alias into the frequency band of interest during the analog-to-digital conversion (ADC) when sampling type (discrete time -DT) ADCs are used [16]. One possible solution is to use an anti-aliasing filter before this ADC, e.g.…”

A microscale optical implant for continuous in vivo monitoring of intraocular pressure

“…Such measurements can only be obtained for up to 24 h because of side complications that accompany long-term use [41][42][43] . To overcome the aforementioned limitations, implants based on radio-frequency (RF) technologies have been used to monitor endovascular pressure 44 , intracranial pressure (ICP) 45,46 , and IOP [47][48][49][50][51][52][53][54][55][56][57][58] . The typical size of these implants ranges from a millimeter to a few centimetres.…”