Noninvasive glucose monitoring with optical heterodyne technique

Noncontact Optical Measurement of Aqueous Humor Glucose Levels and Correlation with Serum Glucose Levels in Rabbit

The noninvasive measurement of serum glucose levels has been investigated for the monitoring of blood sugar control in diabetes. In our study, we aimed to develop a novel noncontact glucometer (NCGM) utilizing an optical approach to measure the intraocular aqueous humor glucose levels in the anterior chamber of rabbit eyes. The NCGM consists of a hybrid optical system that simultaneously measures near-infrared absorption and the polarized rotatory distribution of glucose molecules in the aqueous humor. In vitro optical measurements demonstrated that NCGM measurements had high precision and repeatability for different glucose levels, including 50 mg/dL (14.36%), 100 mg/dL (−4.05%), 200 mg/dL (−5.99%), 300 mg/dL (4.86%), 400 mg/dL (−2.84%), 500 mg/dL (−0.11%), and 600 mg/dL (4.48%). In the rabbit experiments, we found a high correlation between aqueous glucose levels and serum glucose levels, with a mean difference of 8 mg/dL. According to the testing results, the in vivo NCGM measurement of aqueous humor glucose levels also displayed a high correlation with serum glucose levels, with a mean difference of 29.2 mg/dL. In conclusion, aqueous humor glucose levels were accurately measured using the NCGM, and the results correlated with serum glucose levels.

Refractive Changes Associated with Diabetes Mellitus

BACKGROUND AND METHODS

Diabetes mellitus is the most prevalent endocrinedisease in developed countries. In people with diabetes in addition to visionloss caused by diabetic retinopathy transient visual disturbances may occurfrequently caused by refractive changes. These changes in refraction are associated with variations in blood glucose levelsbut the underlying mechanism is still not fully understood. A systematic reviewwith a comprehensive literature search was performed in order to clarify the underlyingmechanisms regarding the connection of glycaemic control and refractive shift.

RESULTS

Some studies have shown that increasedblood sugar leads to a myopic shift whilst others demonstrated that this changeis in a hyperopic direction. Changes in visual acuity in patients with diabetescould be an indicator of inadequate metabolic control or even the first sign ofdiabetes mellitus.

CONCLUSION

This reviewgives a brief overview of current research regarding potential mechanisms ofglycemic control influence on refractive error. The aim isto emphasizethe importance ofunderstanding the relationship ofblood glucose concentration and refractive changes as one of thecommon but overlooked diabetic complications.

Non-invasive polarimetric measurement of glucose concentration in the anterior chamber of the eye

BACKGROUND

Diabetes mellitus is one of the most common diseases in industrialized countries as well as in emerging economies such as India or China. One of the key technologies for diabetes therapy is semi-continuous monitoring of the glucose level of diabetics.

METHODS

Compared with skin-perforating techniques, optical measurement techniques promising good results bear the potential for high patient compliance with more frequent measurements. Due to its excellent optical properties, the anterior chamber and the aqueous humor (AH) contained therein offer promise for non-invasive in vivo glucose measurements. However, a number of strongly limiting factors, such as the precise optical properties of the eye, laser safety regulations and subconscious eye movements during the measurement period have to be considered for in vivo applications.

RESULTS

This article presents a high-resolution polarimetric measurement system that utilizes the optical rotatory dispersion (optical activity) of the glucose molecule for measurements of the glucose concentration in AH.

CONCLUSION

Based on this example of a suitable optical measurement system, the special limitations and conditions that have to be considered for in vivo glucose measurement at the human eye are presented and analyzed. This includes the optical properties of the cornea and the anterior chamber, the impact of typical eye movements during a measurement and laser safety regulations.

Non-invasive glucose measurement technologies: an update from 1999 to the dawn of the new millennium

There are three main issues in non-invasive (NI) glucose measurements: namely, specificity, compartmentalization of glucose values, and calibration. There has been progress in the use of near-infrared and mid-infrared spectroscopy. Recently new glucose measurement methods have been developed, exploiting the effect of glucose on erythrocyte scattering, new photoacoustic phenomenon, optical coherence tomography, thermo-optical studies on human skin, Raman spectroscopy studies, fluorescence measurements, and use of photonic crystals. In addition to optical methods, in vivo electrical impedance results have been reported. Some of these methods measure intrinsic properties of glucose; others deal with its effect on tissue or blood properties. Recent studies on skin from individuals with diabetes and its response to stimuli, skin thermo-optical response, peripheral blood flow, and red blood cell rheology in diabetes shed new light on physical and physiological changes resulting from the disease that can affect NI glucose measurements. There have been advances in understanding compartmentalization of glucose values by targeting certain regions of human tissue. Calibration of NI measurements and devices is still an open question. More studies are needed to understand the specific glucose signals and signals that are due to the effect of glucose on blood and tissue properties. These studies should be performed under normal physiological conditions and in the presence of other co-morbidities.