A compact-size packaged third-order harmonic tag for intraocular pressure (IOP) monitoring inside a mouse eye

This paper shows measurement of intraocular pressure (IOP) within a mouse eye. Three main challenges faced the development of a device for the measurement: the size of the mouse eye, the depth of the anterior chamber where the device will be implanted, and the maximum allowable incision size. These factors all limit the size of the device. In addition, a novel detection scheme is required which enables detection of changes in IOP with high resolution. This paper presents the fabrication process of an ultra-small size Parylene tag in which a micro-electromechanical systems (MEMS) capacitive pressure sensor is packaged with a self-expandable Nitinol antenna and a diode. From the device implanted inside the mouse eye, a resonance frequency shift of the third-order harmonic signal was detected with a sensitivity of approximately 1.5 MHz/mmHg at an 11.5 cm distance from the sensor as the pressure inside the mouse eye changed. This work thus shows the feasibility of IOP monitoring using the third order harmonic from a device implanted inside the mouse eye.