ABSTRACT
We are developing a photonic crystal contact lens sensor for the noninvasive deter-
mination of glucose in tear fluid. Success requires a photonic crystal sensor with
the sensitivity to glucose required to differentiate normal levels from hyperglycemic
and hypoglycemic levels. In addition, the tear glucose levels need to track those of
blood. In this chapter we review our progress in developing a photonic crystal glu-
cose sensor for incorporation into a contact lens. We also review all previous tear
fluid glucose studies, which, while suggesting that tear glucose concentrations tracks
that of blood, significantly disagree as to the tear glucose concentrations in both nor-
mal and diabetic subjects. These studies also disagree as to the relationship between
blood and tear fluid glucose concentrations. We also present new measurements of
tear glucose concentrations by using a method designed to avoid tear stimulation.
We conclude that the various previous tear collection methods biased the measured
tear glucose concentrations. We also review recent studies which attempt to monitor
tear glucose concentrations in situ by using contact lens-based sensing devices. On
the basis of these results, we are optimistic about the future of in vivo tear glucose
sensing.
