Glucose monitoring

Non-invasive blood glucose monitoring

Diabetes Mellitus

Diabetes mellitus is one of the most widespread diseases in modern affluent society. According to estimates by the International Diabetes Federation (IDF), around 170 million people worldwide are currently affected by this disease. The body is unable or only partially able to regulate the glucose content of the blood (blood sugar level). Diabetes patients therefore have to measure their blood glucose levels several times a day to adhere to individual diet plans or - in more severe cases - inject insulin to regulate them.

The most common variant, accounting for 95% of cases, is type II diabetes ("adult-onset diabetes"), which is usually insulin-independent. As the causes of type II are mainly due to poor diet and lack of exercise, this type of the disease mainly occurs in old age. As diabetes significantly accelerates the ageing of the lens of the eye (intraocular lens, IOL), a significant proportion of diabetics must receive an artificial IOL relatively early.

Glucose monitor

Diabetics must continuously monitor their blood glucose levels. The measurement is usually carried out by taking very small amounts of blood, which requires the skin to be perforated. Due to the frequent measurements, this places considerable strain on the affected areas of skin.

The Institute is therefore developing a compact, non-invasive measuring device that significantly increases the acceptance of frequent measurements and the quality of life of patients. More frequent measurements are necessary to avoid long-term damage and thus increase life expectancy.

Measuring principles

Various optical methods are available as non-invasive and non-contact measurement principles. Due to its excellent optical properties, the anterior chamber of the eye is a very favorable measuring location. The fluid contained therein, the aqueous humor, consists largely of blood serum and therefore reflects the glucose content of the blood with a certain latency.

Taking into account the laser protection guidelines, a beam of light can be directed onto the lens of the eye for optical measurement of the glucose concentration, which is then reflected outwards and thus passes through the aqueous humor twice. This reflected light is then analyzed and conclusions can be drawn about the glucose content of the aqueous humor or the blood glucose level.

Two optical properties of the glucose molecule lend themselves to this measurement principle:

• Absorption
  Different wavelengths ("colors") of incident light are absorbed to different degrees depending on the glucose concentration. A spectral analysis of the light reflected by the lens of the eye can be used to determine the glucose concentration in the anterior chamber of the eye and thus the blood glucose level.
• Optical activity
  The polarization properties of the incident light are changed depending on the glucose concentration (rotation of the polarization plane) and can be measured using a highly accurate polarimeter. Here too, the beam reflected by the lens is analyzed to determine the blood glucose concentration.

Implants

Previous non-invasive measurement methods have so far failed due to the extremely low reflective properties within the eye. Only approx. 0.05% of the irradiated light is reflected by the lens. As laser safety guidelines only permit a very low light power density on the eye, optical measurement on the eye is therefore extremely difficult. A promising solution to this problem is the use of miniature implants.

• Modified intraocular lens
  As already described, a large proportion of type II diabetes patients require an artificial eye lens anyway, as the natural lens is so clouded that vision increasingly deteriorates (cataract). Replacing the natural lens with an artificial IOL is often performed on an outpatient basis. The actual minimally invasive operation is performed through an incision of only 2 mm in length and only takes about 20 minutes per eye. Together with industrial partners, the working group is therefore developing a special IOL that is transparent in the wavelength range visible to humans and highly reflective in the wavelength range of the measuring lasers used. In this way, the weaknesses of polarimetry and spectroscopy can be compensated for.
• Implanted passive sensors
  As all optical effects within the eye are very weak and therefore not so easy to measure, the use of other chemical or physical effects is obvious. An implantable passive miniature sensor is therefore being developed at the Institute. Similar to artificial eye lenses, this can be implanted minimally invasively. A non-contact optical measurement method is used to read the sensor. This sensor will enable patients to determine their blood glucose level frequently, quickly and easily.

Integration

The aim of the development is a handheld system the size of binoculars that is easy to use. This system can then be conveniently carried by the patient, allowing measurements to be taken as frequently as required with a measurement time of approx. 20 seconds and without stress for the patient and without the need to take blood samples. The sensor will be based on an optical measuring principle and will therefore be able to measure the glucose concentration in the eye non-invasively and contact-free and reliably determine the blood glucose concentration of the blood on this basis.

The glucose monitor will then be integrated into the ITIV's telemonitoring platform, enabling it to reliably collect and analyze all the statistical data required for diagnosis and therapy, thus relieving the burden on diabetes patients.

Projects

Personal Health Monitor (PHMon)