A method of non-invasively measuring the presence, absence or concentration of one or more analytes in an ocular element of a subject, the subject including an eye with an ocular surface and a tear layer, includes exposing at least a portion of the tear layer and/or other ocular elements of the subject to electromagnetic radiation without contact with the ocular surface; detecting electromagnetic radiation reflected from the tear layer and/or other ocular elements without contact with the ocular surface; and determining a radiation signature of the reflected electromagnetic radiation to determine the presence, absence or concentration of the one or more analytes in the tear layer and/or other ocular elements of the subject.