Pressure sensors in the eye

Sensors can monitor production processes, unmask tiny cracks in aircraft hulls and determine the amount of laundry in a washing machine. In future, they will also be used in the human body and raise the alarm in the event of high pressure in the eye, bladder or brain.

A sensor has been developed by researchers at the Fraunhofer Institute for Microelectric Circuits and Systems IMS in Duisburg.

"We integrate the 2.5 by 2.6 millimetre sensor in an artificial lens," said 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 (also known as glaucoma) 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," said 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.

The sensor is also expected to benefit patients suffering from increased intracranial pressure or those with incontinence problems.