Monitoring glucose concentration in aqueous humor can include inserting an implantable device into an eye and determining glucose concentration as a function of glucose sensed at the implantable device. In some implantable device embodiments, the device includes a polymer layer comprising a material that changes volume in response to varying glucose concentrations of the aqueous humor. A pressure sensor in the device can detect the changes in volume. In some implantable device embodiments, the device includes electrodes for determining the glucose concentration.
