We present an integrated functional contact lens, composed of a differential glucose sensor module, metal interconnects, sensor read-out circuit, antenna and telecommunication circuit, to monitor tear glucose levels wirelessly, continuously and non-invasively. The electrochemical differential sensor module is based on immobilization of activated and de-activated glucose oxidase. We characterized the sensor on a model polymer eye and determined that it showed good repeatability, molecular interference rejection and linearity in the range of 0-2mM glucose, covering normal tear glucose concentrations (0.1-0.6mM). We also report the temperature, ageing and protein-fouling sensitivity of the sensor. We report the design and implementation of a low-power (3W) sensor read-out and telecommunication circuit to deliver wireless power and transmit data for the sensor module. Using this small chip (0.36mm 2), we produced an integrated contact lens with sensors and demonstrated wireless operation of the system and glucose read-out over the distance of several centimeters.