Microfabricated Implantable Parylene-Based Wireless Passive Intraocular Pressure Sensors

This paper presents an implantable parylene-based wireless pressure sensor for biomedical pressure sensing applications specifically designed for continuous intraocular pressure (IOP) monitoring in glaucoma patients. It has an electrical LC tank resonant circuit formed by an integrated capacitor and an inductor coil to facilitate passive wireless sensing using an external interrogating coil connected to a readout unit. Two surface-micromachined sensor designs incorporating variable capacitor and variable capacitor/inductor resonant circuits have been implemented to realize the pressure-sensitive components. The sensor is monolithically microfabricated by exploiting parylene as a biocompatible structural material in a suitable form factor for minimally invasive intraocular implantation. Pressure responses of the microsensor have been characterized to demonstrate its high pressure sensitivity (> 7000 ppm/mmHg) in both sensor designs, which confirms the feasibility of pressure sensing with smaller than 1 mmHg of resolution for practical biomedical applications. A six-month animal study verifies the in vivo bioefficacy and biostability of the implant in the intraocular environment with no surgical or postoperative complications. Preliminary ex vivo experimental results verify the IOP sensing feasibility of such device. This sensor will ultimately be implanted at the pars plana or on the iris of the eye to fulfill continuous, convenient, direct, and faithful IOP monitoring

Wireless Intraocular Pressure Sensing Using Microfabricated Minimally Invasive Flexible-Coiled LC Sensor Implant

This paper presents an implant-based wireless pressure sensing paradigm for long-range continuous intraocular pressure (IOP) monitoring of glaucoma patients. An implantable parylene-based pressure sensor has been developed, featuring an electrical LC-tank resonant circuit for passive wireless sensing without power consumption on the implanted site. The sensor is microfabricated with the use of parylene C (poly-chlorop- xylylene) to create a flexible coil substrate that can be folded for smaller physical form factor so as to achieve minimally invasive implantation, while stretched back without damage for enhanced inductive sensor–reader coil coupling so as to achieve strong sensing signal. A data-processed external readout method has also been developed to support pressure measurements. By incorporating the LC sensor and the readout method, wireless pressure sensing with 1-mmHg resolution in longer than 2-cm distance is successfully demonstrated. Other than extensive on-bench characterization, device testing through six-month chronic in vivo and acute ex vivo animal studies has verified the feasibility and efficacy of the sensor implant in the surgical aspect, including robust fixation and long-term biocompatibility in the intraocular environment. With meeting specifications of practical wireless pressure sensing and further reader development, this sensing methodology is promising for continuous, convenient, direct, and faithful IOP monitoring

Implantable parylene-based wireless intraocular pressure sensor

This paper presents a novel implantable, wireless, passive pressure sensor for ophthalmic applications. Two sensor designs incorporating surface-micromachined variable capacitor and variable capacitor/inductor are implemented to realize the pressure sensitive components. The sensor is monolithically microfabricated using parylene as a biocompatible structural material in a suitable form factor for increased ease of intraocular implantation. Pressure responses of the microsensor are characterized on-chip to demonstrate its high pressure sensitivity (> 7000 ppm/mmHg) with mmHg level resolution. An in vivo animal study verifies the biostability of the sensor implant in the intraocular environment after more than 150 days. This sensor will ultimately be implanted at the pars plana or iris of the eye to fulfill continuous intraocular pressure (IOP) monitoring in glaucoma patients

Implantable micromechanical parylene-based pressure sensors for unpowered intraocular pressure sensing

This paper presents the first implantable, unpowered, parylene-based microelectromechanical system (MEMS) pressure sensor for intraocular pressure (IOP) sensing. From in situ mechanical deformation of the compliant spiral-tube structures, this sensor registers pressure variations without electrical or powered signal transduction of any kind. Micromachined high-aspect-ratio polymeric hollow tubes with different geometric layouts are implemented to obtain high-sensitivity pressure responses. An integrated device packaging method has been developed toward enabling minimally invasive suture-less needle-based implantation of the device. Both in vitro and ex vivo device characterizations have successfully demonstrated mmHg resolution of the pressure responses. In vivo animal experiments have also been conducted to verify the biocompatibility and functionality of the implant fixation method inside the eye. Using the proposed implantation scheme, the pressure response of the implant can be directly observed from outside the eye under visible light, with the goal of realizing convenient, direct and faithful IOP monitoring in glaucoma patients

A Micromechanical Parylene Spiral-Tube Sensor and Its Applications of Unpowered Environmental Pressure/Temperature Sensing

A multi-function micromechanical pressure/temperature sensor incorporating a microfabricated parylene spiral tube is presented. Its visible responses in expression of in situ rotational tube deformation enable unpowered sensing directly from optical device observation without electrical or any powered signal transduction. Sensor characterizations show promising pressure (14.46°/kPa sensitivity, 0.11 kPa resolution) and temperature (6.28°/°C sensitivity, 0.24 °C resolution) responses. Depending on different application requests, this sensor can be individually utilized to measure pressure/temperature of systems having one property varying while the other stabilized, such as intraocular or other in vivo pressure sensing of certain apparatus inside human bodies or other biological targets. A straightforward sensor-pair configuration has also been implemented to retrieve the decoupled pressure and temperature readouts, hence ultimately realizes a convenient environmental pressure and temperature sensing in various systems

Generalized Parity-Time Symmetry Condition for Enhanced Sensor Telemetry

Wireless sensors based on micro-machined tunable resonators are important in a variety of applications, ranging from medical diagnosis to industrial and environmental monitoring.The sensitivity of these devices is, however, often limited by their low quality (Q) factor.Here, we introduce the concept of isospectral party time reciprocal scaling (PTX) symmetry and show that it can be used to build a new family of radiofrequency wireless microsensors exhibiting ultrasensitive responses and ultrahigh resolution, which are well beyond the limitations of conventional passive sensors. We show theoretically, and demonstrate experimentally using microelectromechanical based wireless pressure sensors, that PTXsymmetric electronic systems share the same eigenfrequencies as their parity time (PT)-symmetric counterparts, but crucially have different circuit profiles and eigenmodes. This simplifies the electronic circuit design and enables further enhancements to the extrinsic Q factor of the sensors

FM Continuous Monitoring of Intraocular Pressure, an Engineering Perspective

This chapter discusses the problem of continuously monitoring intraocular pressure (IOP) from an engineering perspective. It is aimed to all public in general although we think that medical staff and engineers may benefit the most from it. Although equations are included for engineers to get a glimpse of how the system works, this chapter does not go into great detail in mathematics and physics to make it understandable to medical staff. It provides though references for engineers who wish to get a better understanding of key subjects tackled in this chapter. The chapter is organized as follows: Section 1 introduces intraocular pressure (IOP) and need for its continuous monitoring. Section 2 describes the most recent efforts to develop a continuous IOP monitoring system. Section 3 shows what medical and engineering considerations must be taken into account to effectively measure IOP. Section 4 deals with health issues due to tissue warming and how to prevent them. Section 5 explains how an implant can be fabricated using either passive electronic components or active ones. Finally, Section 6 explains how the pressure sensor and the electronic circuits can be integrated

Wearable smart sensor systems integrated on soft contact lenses for wireless ocular diagnostics

Wearable contact lenses which can monitor physiological parameters have attracted substantial interests due to the capability of direct detection of biomarkers contained in body fluids. However, previously reported contact lens sensors can only monitor a single analyte at a time. Furthermore, such ocular contact lenses generally obstruct the field of vision of the subject. Here, we developed a multifunctional contact lens sensor that alleviates some of these limitations since it was developed on an actual ocular contact lens. It was also designed to monitor glucose within tears, as well as intraocular pressure using the resistance and capacitance of the electronic device. Furthermore, in-vivo and in-vitro tests using a live rabbit and bovine eyeball demonstrated its reliable operation. Our developed contact lens sensor can measure the glucose level in tear fluid and intraocular pressure simultaneously but yet independently based on different electrical responses.ope

Association of Intraocular Pressure With Human Immunodeficiency Virus

PURPOSE: Prior studies have shown an association between human immunodeficiency virus (HIV) and reduced intraocular pressures (IOP). The purpose of this study was to determine if patients with HIV on highly active antiretroviral therapy (HAART) had any difference in their IOP compared with patients without HIV or with HIV who are not on HAART. DESIGN: Retrospective cross-sectional study. METHODS: We included 400 patients from our academic eye center between 2000 and 2016. Group 1 (G1) consisted of patients with HIV on HAART (n = 176), Group 2 (G2) consisted of patients with HIV who were not on HAART (n = 48), and Group 3 (G3) consisted of controls without HIV (n = 176). An analysis of variance (ANOVA) was performed to compare mean IOP values. Multivariate linear and logistic regression models were performed to assess factors impacting IOP. Difference in IOP was the primary outcome being measured. RESULTS: The mean IOPs in mm Hg were 13.7 +/- 5.1 (G1), 13.1 +/- 3.6 (G2), and 17.3 +/- 3.8 (G3), P \u3c .01. In regression modeling, having a CD4 count CONCLUSIONS: Absolute CD4 counts may play a role in IOP fluctuations. This association was found in patients with HIV regardless of whether patients were on HAART

Corticosteroid implants for chronic non-infectious uveitis.

BACKGROUND: Uveitis is a term used to describe a heterogeneous group of intraocular inflammatory diseases of the anterior, intermediate, and posterior uveal tract (iris, ciliary body, choroid). Uveitis is the fifth most common cause of vision loss in high-income countries, accounting for 5% to 20% of legal blindness, with the highest incidence of disease in the working-age population.Corticosteroids are the mainstay of acute treatment for all anatomical subtypes of non-infectious uveitis and can be administered orally, topically with drops or ointments, by periocular (around the eye) or intravitreal (inside the eye) injection, or by surgical implantation. OBJECTIVES: To determine the efficacy and safety of steroid implants in people with chronic non-infectious posterior uveitis, intermediate uveitis, and panuveitis. SEARCH METHODS: We searched CENTRAL (which contains the Cochrane Eyes and Vision Trials Register) (Issue 10, 2015), Ovid MEDLINE, Ovid MEDLINE In-Process and Other Non-Indexed Citations, Ovid MEDLINE Daily, Ovid OLDMEDLINE (January 1946 to November 2015), EMBASE (January 1980 to November 2015), PubMed (1948 to November 2015), Latin American and Caribbean Health Sciences Literature Database (LILACS) (1982 to November 2015), the metaRegister of Controlled Trials (mRCT) (www.controlled-trials.com) (last searched 15 April 2013), ClinicalTrials.gov (www.clinicaltrials.gov), and the World Health Organization (WHO) International Clinical Trials Registry Platform (ICTRP) (www.who.int/ictrp/search/en). We did not use any date or language restrictions in the electronic search for studies. We last searched the electronic databases on 6 November 2015.We also searched reference lists of included study reports, citation databases, and abstracts and clinical study presentations from professional meetings. SELECTION CRITERIA: We included randomized controlled trials comparing either fluocinolone acetonide (FA) or dexamethasone intravitreal implants with standard-of-care therapy with at least six months of follow-up after treatment. We included studies that enrolled participants of all ages who had chronic non-infectious posterior uveitis, intermediate uveitis, or panuveitis with vision that was better than hand-motion. DATA COLLECTION AND ANALYSIS: Two review authors independently reviewed studies for inclusion. Two review authors independently extracted data and assessed the risk of bias for each study. MAIN RESULTS: We included data from two studies (619 eyes of 401 participants) that compared FA implants with standard-of-care therapy. Both studies used similar standard-of-care therapy that included administration of prednisolone and, if needed, immunosuppressive agents. The studies included participants from Australia, France, Germany, Israel, Italy, Portugal, Saudi Arabia, Spain, Switzerland, Turkey, the United Kingdom, and the United States. We assessed both studies at high risk of performance and detection bias.Only one study reported our primary outcome, recurrence of uveitis at any point during the study through 24 months. The evidence, judged as moderate-quality, showed that a FA implant probably prevents recurrence of uveitis compared with standard-of-care therapy (risk ratio (RR) 0.29, 95% confidence interval (CI) 0.14 to 0.59; 132 eyes). Both studies reported safety outcomes, and moderate-quality evidence showed increased risks of needing cataract surgery (RR 2.98, 95% CI 2.33 to 3.79; 371 eyes) and surgery to lower intraocular pressure (RR 7.48, 95% CI 3.94 to 14.19; 599 eyes) in the implant group compared with standard-of-care therapy through two years of follow-up. No studies compared dexamethasone implants with standard-of-care therapy. AUTHORS\u27 CONCLUSIONS: After considering both benefits and harms reported from two studies in which corticosteroids implants were compared with standard-of-care therapy, we are unable to conclude that the implants are superior to traditional systemic therapy for the treatment of non-infectious uveitis. These studies exhibited heterogeneity in design and outcomes that measured efficacy. Pooled findings regarding safety outcomes suggest increased risks of post-implant surgery for cataract and high intraocular pressure compared with standard-of-care therapy