Non-invasive glucose determination in the human eye

For non-invasive in vivo glucose determinations by means of near-infrared spectroscopy, the anterior chamber of the human eye is a promising site. An optical set-up for the non-invasive glucose determination in the human eye precisely in the anterior chamber with a beam reflected from the surface of the eye lens is presented here. As the anterior chamber has a depth of 3.13±0.50 mm, the beam follows an optical path of 5.3-7.3 mm depending on the angle of incidence, which is individually constant. We will show that it is possible to acquire good concentration predictions for physiological glucose concentrations with such a long optical path. A chemometric study of NIR glucose spectra with concentrations of glucose in water of 10-350 mg/dL (0.56-1.94 mmol/L) resulted in a calibration model which was able to predict physiological glucose concentrations with a root mean square error of prediction RMSEPTest=15.41 mg/dL. The Clarke error grid diagram shows that the model performs well according to medical impact. Using a first in vivo set-up, the precision is not sufficient for a reliable prediction of glucose concentration, especially due to the flickering of the patient's eye and the low reflectivity of the eye lens. Therefore, we have designed a new in vivo set-up: a prototype for a self-monitoring device with controlled geometry and laser radiation at several distinct wavelengths instead of the halogen lamp as light source. This allows a far higher signal/noise ratio under much better reproducible geometrical conditions and at the same time a much smaller necessary light flux.