TECHNOLOGY FOR CHANGE

Smart Contact Lens Detects Eye Disease

R. Colin Johnson | Date: 04-21-10 | Comments

By embedding a micro-electro-mechanical system (MEMS) chip into a contact lens, wireless medical electronics can monitor intermittent symptoms of eye disease by recording a whole day's worth of sensor readings.

Many diseases today have symptoms that occur at irregular intervals, making it hit-or-miss as to whether the doctor happens to test for a particular symptom at the specific moment that it is manifesting itself. Heart doctors have monitoring sensors that they can attach to the patient and send them home with so that readings can be recorded for several days, then examined later by the doctor. But for eye doctors, there has been no mobile diagnostic systems until now.

In addition to the strain gauge, the lens contains an antenna, a tiny dedicated processing circuit, and an RF transmitter to communicate the measurements to the receiver.

Sensimed AG (Lausanne, Switzerland), in cooperation with MEMS chip makers STMicroelectronics (Geneva), has designed a contact lens that houses a tiny MEMS pressure sensor and the associated wireless antenna to transmit a whole day�s worth of readings. The first model will help make earlier diagnoses of glaucoma patients.

"This wireless, self-powered, on-body sensor promises to help the millions of people," says Benedetto Vigna, General Manager of STMicroelectronics� MEMS, Sensors, and High Performance Analog division.

Called the Triggerfish, the smart contact lens houses both the embedded strain gauge and metallic ring that encircles the pupil to act as an antenna. The system take measurements of the curvature of the eye over a period of 24 hours, providing eye doctors with a diagnostic tool similar to those already available for heart doctors.

The problem with glaucoma--which leads to blindness, but can be halted if detected early--is that the method of testing for its presence is to measure the intraocular pressure inside the eye, usually by using a tonometer that puffs the eye with air to determine pressure. Unfortunately, intraocular pressure varies widely during the day, making it hit-or-miss whether a patent with glaucoma has it detected during an annual visit. With the Sensimed Triggerfish, on the other hand, a simple 24-hour period should be able to record the entire day�s worth of intraocular pressure readings, which often peak during evening hours and during sleep.

In operation, the patient wears a small receiver box on a cord around his or her neck. The receiver beams power to the antenna on the contact lens as well as receives the transmitted data for recording. The antenna on the contact lens acts like an RFID tag, converting the radio frequency (RF) power beamed to it into usable current to take a measurement with the strain gauge, then transmitting the results back to the receiver box.

The Sensimed Triggerfish smart contact lens has already received the Conformit� Europ�enne (CE mark indicating "European conformity" to consumer safety, health, or environmental requirements), and is already available in Switzerland where it is undergoing clinical trials at the University Hospital (Geneva). Pending regulatory approvals, the smart contact lens will be rolled out country-by-country across Europe starting in the third quarter of 2010, and to the U.S. market by 2011.