Development of Inductive and Capacitive Type Intraocular Pressure (IOP) Sensor to Improve Sensitivity and Minimize Size

Abstract We had presented an inductive type intraocular pressure sensor (L-sensor) in previous work. The distance between a micro coil anda ferrite on the membrane was modulated by pressure, and as a result the inductance and resonant frequency were changed. However,L-sensor has some problems to implant in eyes. First problem is low sensitivity. When L-sensor was implanted in rabbit’s eyes, resonantfrequency of L-sensor was very hard to detect. Second problem is biocompatibility. Size of L-sensor is 6×7×1.2 mm. When L-sensorwas implanted in the eyes, it caused the inflammation. Therefore, this study suggests an inductive and capacitive type IOP sensor (LC-sensor). The sensitivity of the LC-sensor 27.3 kHz/mmHg under 60 mmHg. It is much larger than 14 kHz/mmHg of the L-sensor. Andthe size of LC-sensor is 47% smaller than L-sensor. After 2 weeks from the implantation of LC-sensor into rabbit eyes, we measuredthe changes of resonant frequency of LC-sensor according to increased IOP by Balanced Salt Solution (BSS) injection. As a result, thesensitivity of LC-sensor in in vivo test is 25 kHz/mmHg. That is similar to the sensitivity of in vitro test.Keywords: Glaucoma, Intraocular pressure (IOP), IOP sensor, in vivo, Wireless, Implantable