Diabetes is one of the most common diseases of the modern affluent society. According to the International Diabetes Federation (IDF) an estimation 170 mio. people worldwide are affected by this disease. The body of a diabetic is not or only partially able to control the blood sugar level (glucose level). Hence the patient has to measure his glucose level several times a day in order to maintain his diet or inject insulin to control the glucose level manually in severe cases.
The most common type (about 95% of all diabetics) is the non-insulin-dependant diabetes Type II (also known as adult onset diabetes). Since the main reasons for this type are unbalanced diet and sedentary lifestyle, Type II Diabetes mainly occurs at advanced age. Diabetes also substantially accelerates the aging processes of the natural intraocular lens (IOL) which is why a major part of diabetics is in need of artificial IOLs much earlier then non-diabetics.
Diabetics need to monitor their blood sugar level continuously. This is done by taking small blood samples which then are being assayed for glucose. Due to the need of frequent measurements this leads to substantial stress for the skin permanently prone to perforation.
A non-invasive measurement instrument is currently being developed at ITIV to increase patient compliance and quality of everyday life for even more frequent measurements. The more frequently measurements are taken the better one is able to prevent long term damage and thus increase life span.
Optical measurements are well suited for non-invasive and non-contact measurement systems. Due to its excellent optical qualities the anterior chamber of the human eye is a very interesting target for optical measurements. The contained liquid (aqueous humor) mainly consists of blood serum and hence reflects the blood glucose concentration considering a certain time delay.
Meeting the strongly limiting laser safety regulations a light beam can be directed into the anterior chamber which is reflected by the surface of the IOL. The light crosses the anterior chamber twice and the optical properties of the aqueous humor can be analyzed. Using these measurement results the glucose level respectively the blood sugar level can be derived.
Applying this measurement setup there are two physical effects which may be utilized:
Different wavelengths (“colors”) of the transmitted light will be absorbed with different magnitudes.
Employing spectrum analysis of the light reflected by the IOL the glucose concentration inside the anterior chamber can be measured and the blood sugar level can be derived.
Optical Rotatory Dispersion
Depending on the glucose concentration in the anterior chamber the polarization properties of the transmitted light are being altered (rotation of the polarization plane of linearly polarized light). Using a high resolution polarimeter these effects can be measured. Just like spectroscopy the method of polarimetry analyzes the reflected light of the IOL and thereof derives the blood sugar level.
Optical measurement principles at the human eye analyzed by several research groups so far have all miscarried due to the same fundamental problem: The extremely small measurement signal i.e. the tiny amount of light which is being reflected by the IOL and holds the valuable information about the glucose concentration. Only a percentage of about 0.05% of the incoming light is reflected by the human IOL. Together with safety regulations which strongly limit the allowed optical power density at the retina, optical measurement techniques at the human anterior chamber are at the edge of feasibility. A very promising option to solve this problem are miniaturized passive implants.
Modified Intraocular Lens
As mentioned before a large part of the Type II diabetics are in need of an artificial IOL since their natural lens has become dull and rigid due to aging processes which is why vision is fading continuously (Cataract). Replacement of the natural lens by an artificial IOL is usually done ambulatorily. The minimally invasive operation itself takes about 20 minutes per eye and is done via a cut of only 2mm length.
Together with industrial partners ITIV is developing a specialized IOL which will transmit the visible light and strongly reflect the wavelengths of the lasers in use relevant to the measurement.
This way the deficiency of polarimetry as well as spectroscopy can be compensated.
Implantable Passive Sensors
All usable optical effects inside the eye only offer very small signal magnitudes and are hard to detect. While further chemical and physical effects offer much higher magnitudes utilizing such effects seems obvious.
A passive implantable miniaturized sensor is being developed at ITIV. Using the same minimal-invasive implantation techniques used in modern IOL implantation such a miniaturized sensor could be easily implanted. For information readout a non-contact optical measurement technique will be employed. Such a sensor will enable diabetics to conduct more frequent, painless and easy-to-do measurements..
The target system for the development is a binocular-sized handheld system . This device will be mobile and handy to be used anywhere and anytime. In this way the measurements with duration of only 20 seconds can be repeated as often as desired and the blood sugar level can be determined reliably without inconvenient perforation of the skin. The sensor itself will be measuring the glucose level of the anterior chamber based on an optical measurement technique.
The glucose monitor will be integrated into the ITIV telemonitoring platform and collecting and analyzing reliable statistical data needed for diagnosis and therapy to relieve the patient.
Personal Health Monitor (PHMon)