A device for measuring an analyte concentration level in a subject. The device includes: a light source configured for illuminating at least a portion of an anterior region of an eye of the subject with incident light having a substantially broad illumination spectrum at an angle substantially tangential to the surface of the eye; an optical collector configured for detecting reflected light from the at least a portion of the anterior region of the eye; an analyzer configured for analyzing the detected reflected light; and a processor configured to determine the analyte concentration level in the subject based on the analyzed reflected light.