Brian C. Samuels

A Minimally Invasive Implantable Wireless Pressure Sensor for Continuous IOP Monitoring

This paper presents a minimally invasive implantable pressure sensing transponder for continuous wireless monitoring of intraocular pressure (IOP). The transponder is designed to make the implantation surgery simple while still measuring the true IOP through direct hydraulic contact with the intraocular space. Furthermore, when IOP monitoring is complete, the design allows physicians to easily retrieve the transponder. The device consists of three main components: 1) a hypodermic needle (30 gauge) that penetrates the sclera through pars plana and establishes direct access to the vitreous space of the eye; 2) a micromachined capacitive pressure sensor connected to the needle back-end; and 3) a flexible polyimide coil connected to the capacitor forming a parallel LC circuit whose resonant frequency is a function of IOP. Most parts of the sensor sit externally on the sclera and only the needle penetrates inside the vitreous space. In vitro tests show a sensitivity of 15 kHz/mmHg with approximately 1-mmHg resolution. One month in vivo implants in rabbits confirm biocompatibility and functionality of the device.

Clinical Profiles of Primary Open Angle Glaucoma versus Normal Tension Glaucoma Patients: A Pilot Study

Purpose: To study the health profiles and behavioral differences between primary open angle glaucoma (POAG) and normal tension glaucoma (NTG) patients. Methods: Confidential mail survey of ICD-9 defined POAG (n = 277) and NTG (n = 116) patients was carried out to collect information regarding age, gender, height, weight, waist circumference, blood pressure (BP), medications [prescription (Rx) and over the counter (OTC)], education, and the Short Health Anxiety Inventory (SHAI). Results: NTG patients (59/116) were significantly more likely to respond to the survey than POAG patients (43/277), p = 0.0001, and to have obtained college level education (70% vs. 42%), p = 0.003. Body weight, waist circumference, body mass index, systolic BP, pulse pressure, and ratio of prescription medications to OTC medications were significantly lower in the NTG group (p < 0.0001). The SHAI score, mean age, and diastolic BP were not different between the two groups. A subgroup analysis of college-educated patients in both groups revealed persisting significant differences in waist circumference, systolic BP, and ratio of Rx to OTC medications. Conclusions: NTG patients do not have significantly greater health anxiety than POAG patients. NTG patients are more likely to have lower BMI, systolic BP, and ratio of Rx to OTC medications than POAG patients. The pilot nature of this study limits generalizability of these findings. Larger studies confirming these findings and elucidating the role of refractive error and medical history on such differences are needed.