A user-wearable device comprising: a frame configured to mount on a user; a display attached to the frame, the display configured to direct virtual images to an eye of the user; a light source (1640; 1700) configured to provide polarized light to the eye of the user, wherein the light source comprises a polarization controller comprising at least one optical fiber and at least one piezo-electric actuator configured to apply pressure on the at least one optical fiber such that the optical fiber controls a polarization state of the polarized light provided to the eye of the user, wherein the at least one piezo-electric actuator is configured to apply pressure on the at least one optical fiber such that the optical fiber rotates the polarization state including polarization angle of the polarized light provided to the eye of the user; a light analyzer configured to determine the polarization angle rotation of the light reflected from the eye of the user; one or more sensors (24, 28, 30, 32, 34) attached to the frame, the one or more sensors configured to sense information relating to the user or environment; and processing electronics in communication with the light analyzer and the one or more sensors (24, 28, 30, 32, 34), the processing electronics configured to: determine a glucose level of the user based at least in part on the polarization angle rotation of the light reflected from the eye of the user; receive from the one or more sensors (24, 28, 30, 32, 34) the information relating to the user or the environment; and store and access the received information. a frame configured to mount on a user; a display attached to the frame, the display configured to direct virtual images to an eye of the user; a light source (1640; 1700) configured to provide polarized light to the eye of the user, wherein the light source comprises a polarization controller comprising at least one optical fiber and at least one piezo-electric actuator configured to apply pressure on the at least one optical fiber such that the optical fiber controls a polarization state of the polarized light provided to the eye of the user, wherein the at least one piezo-electric actuator is configured to apply pressure on the at least one optical fiber such that the optical fiber rotates the polarization state including polarization angle of the polarized light provided to the eye of the user; a light analyzer configured to determine the polarization angle rotation of the light reflected from the eye of the user; one or more sensors (24, 28, 30, 32, 34) attached to the frame, the one or more sensors configured to sense information relating to the user or environment; and processing electronics in communication with the light analyzer and the one or more sensors (24, 28, 30, 32, 34), the processing electronics configured to: determine a glucose level of the user based at least in part on the polarization angle rotation of the light reflected from the eye of the user; receive from the one or more sensors (24, 28, 30, 32, 34) the information relating to the user or the environment; and store and access the received information. determine a glucose level of the user based at least in part on the polarization angle rotation of the light reflected from the eye of the user; receive from the one or more sensors (24, 28, 30, 32, 34) the information relating to the user or the environment; and store and access the received information.