title: Preliminary study on implantable inductive-type sensor for continuous monitoring of intraocular pressure.
abstract: BACKGROUND
  This study aims to validate the performance and biocompatibility of an implantable inductive-type sensor for continuous monitoring of intraocular pressure (IOP) METHODS: The sensor is composed of a top layer integrated with an inductor and capacitor circuit, and a bottom layer integrated with ferrite. With IOP change, the sensor's bottom layer is mechanically deflected, which changes the distance between the bottom-layer ferrite and top-layer inductor, resulting in an alteration of inductance magnitude and the resonant frequency (RF). In-vitro measurement was conducted via air pressurization in a sealing jig (n = 3). Subsequently, the sensor was implanted into the anterior chamber of a rabbit eye. In-vivo measurement was performed while the IOP was elevated by infusion of balanced salt solution (BSS, 6 μL/min). Smaller-sized sensors later were implanted into two rabbit eyes, which were microscopically examined at 2, 4 and 8 weeks post-implantation. The eyes were then immediately enucleated for histological examination.
  
  
  RESULTS
  The in-vitro measurement showed a significant RF shift as pressure in the jig was increased from 0 mmHg to 60 mmHg (average initial frequency: 10.86 MHz, average shift: 403 kHz). The in-vivo measurement also showed an RF decrease, from 12.80 MHz to 12.67 MHz, as the pressure was increased from 10 mmHg to 20 mmHg. Microscopic in-vivo evaluations and histological exams, performed at intervals up to 8 weeks post-implantation, showed no evidence of significant inflammation or deformity of the ocular-tissue structures.
  
  
  CONCLUSIONS
  The implantable inductive-type IOP sensor demonstrated wireless pressure-sensing ability and favourable biocompatibility in the rabbit eye.
authors.affiliation: Department of Ophthalmology, Seoul National University College of Medicine, Seoul, Korea.|Department of Ophthalmology, Seoul National University Hospital, Seoul, Korea.
authors.forename: Yong Woo
authors.initials: YW
authors.lastname: Kim
authors.affiliation: Department of Ophthalmology, Seoul National University College of Medicine, Seoul, Korea.|Department of Ophthalmology, Seoul National University Hospital, Seoul, Korea.
authors.forename: Mi Jeung
authors.initials: MJ
authors.lastname: Kim
authors.affiliation: Department of Ophthalmology, Seoul National University College of Medicine, Seoul, Korea.|Department of Ophthalmology, Seoul National University Hospital, Seoul, Korea.
authors.forename: Ki Ho
authors.initials: KH
authors.lastname: Park
authors.affiliation: Department of Ophthalmology, Seoul National University College of Medicine, Seoul, Korea.|Department of Ophthalmology, Seoul National University Hospital, Seoul, Korea.
authors.forename: Jin Wook
authors.initials: JW
authors.lastname: Jeoung
authors.affiliation: Department of Ophthalmology, Seoul National University College of Medicine, Seoul, Korea.|Department of Ophthalmology, Seoul National University Boramae Hospital, Seoul, Korea.
authors.forename: Seok Hwan
authors.initials: SH
authors.lastname: Kim
authors.affiliation: Brain Science Institute/Center for BioMicrosystems, Korea Institute of Science and Technology, Seoul, Korea.|Department of Electronic Engineering, Sogang University, Seoul, Korea.
authors.forename: Cheol In
authors.initials: CI
authors.lastname: Jang
authors.affiliation: Brain Science Institute/Center for BioMicrosystems, Korea Institute of Science and Technology, Seoul, Korea.
authors.forename: Soo Hyun
authors.initials: SH
authors.lastname: Lee
authors.affiliation: Brain Science Institute/Center for BioMicrosystems, Korea Institute of Science and Technology, Seoul, Korea.
authors.forename: Jae Hun
authors.initials: JH
authors.lastname: Kim
authors.affiliation: Brain Science Institute/Center for BioMicrosystems, Korea Institute of Science and Technology, Seoul, Korea.
authors.forename: Seok
authors.initials: S
authors.lastname: Lee
authors.affiliation: Brain Science Institute/Center for BioMicrosystems, Korea Institute of Science and Technology, Seoul, Korea.
authors.forename: Ji Yoon
authors.initials: JY
authors.lastname: Kang
mesh_terms: D000818:Animals; D004867:Equipment Design; D007429:Intraocular Pressure / Q000502:physiology*; D008297:Male; D008422:Materials Testing; D008991:Monitoring, Physiologic / Q000295:instrumentation*; D019736:Prostheses and Implants; D011817:Rabbits; D013686:Telemetry / Q000295:instrumentation; D014065:Tonometry, Ocular / Q000295:instrumentation*
keywords: continuous monitoring; glaucoma; implantable sensor; intraocular pressure