Enhanced Sensitivity of Real-Time Intraocular Pressure Monitoring by Integration of a Wrinkled Gold-Based Capacitive Sensor with Parity-Time Symmetry Wireless Technology.

Glaucoma is an ophthalmic condition characterized by elevated intraocular pressure (IOP) due to the obstruction of aqueous humor flow in the anterior chamber of the eye. This condition can damage the optic nerve, ultimately leading to blindness. Therefore, real-time monitoring of IOP is essential for preventing glaucoma and other ophthalmic diseases. A smart soft contact lens with a capacitive sensor was developed to monitor IOP. The sensor employs a wrinkled gold-film electrode that can stretch by up to 50% of its initial length without a significant change in resistance. A soft dielectric layer composed of Ecoflex supports deformability, stability, and sensitivity. Compared to a flat gold film, the wrinkled type doubles the capacitance response, increasing sensitivity from 393 to 1057 ppm/mmHg. By incorporating a parallel parity-time (PT) symmetry setup for wireless detection and leveraging its near exceptional points characteristics, enhanced coupling and frequency change tracking caused by corneal deformation are achieved, boosting the sensitivity approximately 7.5 times that of the conventional system. The maximum negative impedance of -5000 Ω in the PT symmetry setup is 5 times that of the conventional and 2500 times that of the commercial inductive antenna, enabling clearer IOP detection and superior pressure sensing performance. Lastly, the human corneal epithelial (HCE) cell culture experiments indicate preliminary in vitro biocompatibility.