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Eye sensor offers instant blood glucose readings

02 Nov 2005

A pain-free optical technique for measuring blood glucose levels could prove to be a big hit with diabetics when it comes to the market. Oliver Graydon reports from Photonex 2005.

Taking blood glucose measurements could be as simple as holding a small sensor up to a person's eye and pressing a button if a UK start-up is successful. Lein Applied Diagnostics is developing a hand-held optical sensor that determines the glucose level of a person with diabetes via the eye's aqueous humour.

The attraction of the technique is that it involves no drawing of blood, takes just 0.1 s to perform, and potentially requires no consumables aside from a battery. In contrast, glucose measurements are currently performed by pricking the finger and placing a finger stick with a blood sample into a small analyser four or five times a day. The problem with this approach is that is painful, inconvenient and can be unhygienic.

"The goal is to have a non-invasive device that is quick and easy to use," Dan Daly, a director of Lein Applied Diagnostics, told attendees during a Biophotonics seminar at the Photonex trade show in Coventry, UK, in October. "Other people have explored optical techniques but they nearly all go through the skin. The problem is that the skin's properties are very variable due to changes in temperature and sweat for example, and this leads to inconsistent measurements."

Lein measures the glucose level by focusing light from a low-power 670 nm source into the eye and analysing the reflected light. "The glucose concentration in the aqueous humour is about 80% of that of blood and tracks it with a time lag of no more than 5-10 min," said Daly.

To protect the firm's IP, Daly wouldn't go into details concerning the optical design of his sensor but explained that it uses a confocal arrangement to localize the measurement in the anterior chamber of the eye.

Origins of Lein Applied Diagnostics

"In principle, looking into the eye using techniques like polarimetry, for example, works very well but the problem is that the shape of the cornea and lens continually change and that confuses the measurement," said Daly. "Our innovation is to use a confocal technique to localize the measurement inside the eye and avoid these problems."

The firm, based near Reading, has filed two patents for its idea and built a lab-based prototype device. It is working closely with SIRA, the University of Manchester and the Institute of Photonics at the University of Strathclyde.

According to Daly, the technique is inherently safe as it requires an optical power in the microwatt level and the measurement time is only about 0.1 s. He also believes that it should be compatible with contact lenses.

"We've tested a couple of dozen people and now want to build more advanced prototypes and extend the testing to a larger sample of subjects. The first prototypes used at the University of Manchester last year used LEDs but the current model uses a laser diode which provides a much higher spatial resolution," said Daly. "However, for the next generation of glucose sensor prototype we will use an LED again. People feel more comfortable about shining light from an LED rather than a laser into their eye, even though it's entirely safe."

Lein is also thinking about ways of reducing the size and manufacturing cost of its sensor. The ultimate aim is a small battery-powered device that can be easily carried around in a pocket or handbag.

Daly is confident that by exploiting technology and assembly techniques from the mobile phone, data storage and telecoms industries that this should be possible.

"The optical side of our system is very much like a CD read-head - we have a source, a receiver, the optics and a scanning system to control the location of the measurement," explained Daly. "So what we are looking at making is something similar to a mobile phone with a CD read-head inside. It's a very cost-driven market so we need to be able to make these units very cheaply."

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