Various embodiments of a user-wearable device can comprise a frame configured to mount on a user. The device can include a display attached to the frame and configured to direct virtual images to an eye of the user. The device can also include a light source configured to provide polarized light to the eye of the user and that the polarized light is configured to reflect from the eye of the user. The device can further include a light analyzer configured to determine a polarization angle rotation of the reflected light from the eye of the user such that a glucose level of the user can be determined based at least in part on the polarization angle rotation of the reflected light.
