Comparing the Rise in Glucose Concentration in Blood, Aqueous and Interstitial Fluid During a Glucose Tolerance Test.

Purpose: The purpose of the study was to determine if aqueous glucose levels rise in a comparable time frame to interstitial fluid and could therefore be suitable for a continuous glucose monitoring (CGM) site. Methods: An intravenous glucose tolerance test was performed on five New Zealand white rabbits. Aqueous humor from the posterior and anterior chamber of the eye and venous blood were sampled for glucose concentration measurement. Glucose concentrations in the interstitial fluids were monitored using a CGM system. A compartment model was created to map the glucose response curves in each compartment. The delay in rising glucose concentrations between blood and interstitial fluid and aqueous humor in the posterior chamber and anterior chamber of the eye were analyzed. Results: The results showed a statistically similar time lag and rate of change in glucose concentrations between blood and interstitial fluids or aqueous humor in either the posterior or anterior chamber. Conclusions: The results of this study add further support to the aqueous humor being used as an alternative CGM site. Translational Relevance: The study provides the basis for developing an intraocular continuous glucose sensor that can overcome limitations of current CGM systems.

Evaluation of Electrical Performance and Properties of Electroretinography Electrodes.

Purpose: The aim of this study was to evaluate and compare the electrical performance and properties of commercially available electroretinography (ERG) electrodes. Methods: A passive ionic model was used to measure impedance, noise, and potential drift in 10 types of ocular surface and skin ERG electrodes. Results: The impedance for silver-based ocular electrodes are generally lower (range, 65.35-343.3 Ω) with smaller phase angles (range, -6.41° to -33.91°) than gold-based electrodes (impedance ranged from 285.95 Ω to 2.913 kΩ, and phase angle ranged from -59.65° to -70.01°). Silver-based ocular electrodes have less noise (median line noise of 6.48 x 104nV2/Hz) than gold-based electrodes (median line noise of 2.26 x 105nV2/Hz). Although silver-based electrodes usually achieve a drift rate less than 5 µV/s within 15 minutes, gold-base ocular electrode cannot achieve a stable potential. The exception is the RETeval strip type of silver electrode, which had an unusual drift at 20 minutes. The noise spectral density showed no change over time indicating that noise was not dependent on the stabilization of the electrode. Conclusions: From the range of electrodes tested, lower impedance, lower capacitance, and lower noise was observed in silver-based electrodes. Stabilization of an electrode is effective against drift of the electrode potential difference but not the noise. Translational Relevance: Application of electrodes with optimized materials improve the quality of clinical electrophysiology signals and efficiency of the recording.