Time to debunk another widely covered press story about wonderful new inventions coming from a tech giant. Ars Technica had one of many articles about Google’s “announcement” of a blood glucose sensor in a contact lens. The discussion after the article is good, as often happens with Ars. Here’s my quick explanation of why the concept will fail. Unfortunately.

Non-invasive glucose testing is the perennial “pot of gold at the end of the rainbow.” Google is not the first to try using tears; the others have failed, and they will too. They say it is “5 years away,” which is equivalent to saying “We have not yet tested it on real diabetics.” 

The problem is basically that tears won’t track blood glucose levels closely. Tears are secreted by the lacrimal gland. I’ve never studied it, but the composition of its secretion is sure to depend on a multitude of variables. (Think: sweat, saliva, etc.) Even if a relationship exists and can be quantified  “on average,” there will be lags.

It’s possible that a device like this could supplement other measurement systems.  But nothing will be as good as actual blood measurements.  Therefore finger sticks will always be needed for calibration. The best realistic case is that a contact lens device could serve as an early warning; but finger sticks will still be needed for validation before taking any action.

via Google introduces smart contact lens project to measure glucose levels | Ars Technica.