However, CGM systems are not very accurate. The best continuous monitors are in the 12% to 13% inaccuracy range, and the worst are in the 17% to18% range. In addition, these devices are relatively expensive, costing between $3,000 and $4,000 per year.

“Many patients don’t see value [in] it since there are few good algorithms to help them deal with the large amount of data,” said Ginsberg.

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Technologies on the Horizon

Other technologies in development aim to improve upon the limitations of blood glucose meters and CGM devices. Researchers are developing less invasive approaches than the current standards of care using bodily fluids such as sweat, saliva, urine or tears.

Google is currently developing a smart contact lens to measure glucose in tears continuously using a wireless chip and miniaturized glucose sensor. This chip and sensor are embedded between two layers of soft contact lens material. A tiny pinhole in the lens allows tear fluid from the surface of the eye to seep into the glucose sensor.3

“The Google smart lens has two small chips within the lens, one serving as a glucose sensor and the other for communication. It is likely that they would be developing it to work similar to continuous glucose monitors in the skin, using glucose oxidase that runs inside a chip. However, there have been companies who have tried to do this previously and abandoned the approach,” Ginsberg said.

Yet according to Ginsberg, “The Google smart lens appears to be more sophisticated. It has no internal power source or battery. There is just gold wiring along the edge of the lens. It remains unclear how Google is going to power the device. It is likely that they will power it by running an AC magnetic field across a set of wires … but it also remains unclear where they will put the coils for the magnetic field. It would need to be near the lens and will not be small.”

One concern with this approach is how tear glucose correlates with blood glucose levels.

“Something that may raise some concern is that glucose in the tears is actively secreted at a very low percentage of glucose in blood. Glucose in blood 90 mg/dL. Glucose in tears in 3 mg/dL to 7 mg/dL. Since it is an active filtrate, the cells filtering can change it, which does two things: There may be a long lag [of] 15 minutes, and since it is an active filtrate, the filtering cells can change the ratio of tear glucose to blood glucose. I would worry about a lag in glucose monitoring. The delayed reading can cause problems,” Ginsberg said.

Other technologies may prove to be more accurate and easier to power, such as using an implantable glucose sensor and glucose binding proteins.


  1. U.S. Food and Drug Administration. Blood Glucose Monitoring Devices. Available at: Accessed: September 14, 2014.
  2. Mayo Clinic. Blood Glucose Meter: How to Choose. Available at: Accessed: September 14, 2014.
  3. Google. Official Blog. Introducing Our Smart Lens Project. Available at: Accessed: September 14, 2014.