Apparatus, systems and methods employing contact lenses with two-electrode electrochemical sensors are provided. In some aspects, the contact lens includes: a substrate that forms at least part of a body of the contact lens and a circuit, disposed on or within the substrate, and including a two-electrode electrochemical sensor. The two-electrode electrochemical sensor can include: a working electrode and a combination reference-counter electrode. The electrochemical sensor can be an amperometric sensor that senses a biological feature of a wearer of the contact lens. The working electrode can generate a signal indicative of the sensed analyte, and the combination reference-counter electrode can pass the signal generated from the working electrode. The signal can be employed to determine the analyte concentration of a solution in contact with the contact lens.
