This invention is generally related to a biocompatible sensor for detecting/measuring sugar, especially glucose, in an ocular fluid in a non-invasive or minimally invasive manner and a method for using the biocompatible sensor. A biocompatible sensor of the invention comprises, consists essentially, or consists of an ophthalmic device comprising a molecular sensing moiety which interacts or, reacts with sugar to provide an optical signal which is indicative of sugar level in an ocular fluid.