Pressure sensor for the eye
20 September 2007 A sensor developed by researchers at the Fraunhofer Institute for
Microelectric Circuits and Systems IMS in Duisburg, Germany, can monitor
pressure in the eye, aiding the treatment of glaucoma. It also has potential
to monitor blood pressure and incontinence. If the pressure in the eye is too high, nerve
fibres die, resulting in
visual field loss or blindness. Since increased intraocular pressure, also
known as glaucoma, is not usually painful, the condition is often diagnosed
too late. Moreover, such patients often tend to develop cataracts when they
get older — the lenses of their eyes become opaque.
In such cases, surgeons
remove the natural lens and replace it with an artificial one. To avoid
further loss of nerve fibres, the intraocular pressure is then regulated as
accurately as possible with the help of medication. Unfortunately, the
pressure continues to vary despite medication, obligating the patient to
have it constantly monitored by physicians and the medication dosage
adjusted accordingly.
 The
new sensor will obviate the need for
constant visits to the physician by such patients. “We integrate the 2.5 by
2.6mm sensor in an artificial lens,” says Thomas van den Boom,
group manager for biohybrid systems at the IMS. “This doesn’t impair the
patient’s vision.”
The top and bottom of the sensor are formed by
electrodes; the top electrode is flexible, in contrast to its rigid
counterpart on the bottom of the sensor. When the intraocular pressure
increases, the top electrode is pushed in, reducing the distance between the
top and bottom of the sensor and thus increasing the capacitance.
Using a
tiny antenna, the implant then sends the pressure data to a reader that is
fitted into the frame of a pair of spectacles. The patient can view the
results on an auxiliary device and determine whether the pressure has
reached a critical level. An antenna in the spectacle frame supplies the
sensor with the required energy via an electromagnetic field. “The power
consumption of the sensor must be kept to an absolute minimum,” explains van
den Boom. “All unused components are put in a kind of standby mode and only
activated when needed.”
The permanent eye implant is currently undergoing clinical trials and could
come into general use in two to three years’ time. But the sensor is not
only suitable for use in the eye: When implanted in blood vessels in the
thigh or the upper arm it can also help patients with chronic hypertension.
“Conventional devices for measuring blood pressure at home are not suitable
for determining the correct medication dosage,” says van den Boom. The
sensor is also expected to benefit patients suffering from increased
intracranial pressure or those with incontinence problems. To top
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