An eye-mountable device includes an electrochemical sensor embedded in a polymeric material configured for mounting to a surface of an eye. The electrochemical sensor includes a working electrode, a reference electrode, and a reagent that selectively reacts with an analyte to generate a sensor measurement related to a concentration of the analyte in a fluid to which the eye-mountable device is exposed. The working electrode can have a first side edge and a second side edge. The reference electrode can be situated such that at least a portion of the first and second side edges of the working electrode are adjacent respective sections of the reference electrode.