Pressure detector

A smart contact lens that continuously monitors the pressure inside the eye could revolutionise the diagnosis and treatment of glaucoma.

A circular antenna taped around the eye not only powers the electronic components in the contact lens, but also acts to receive the data from the lens. The antenna is connected to a battery-powered recorder the size of an iPod through a thin flexible cable, which stores the information until it can be wirelessly uploaded to an ophthalmologist’s computer at the end of the monitoring session.

To monitor the pressure of the eye, the soft hydrophilic silicone disposable contact lens has within it a micro electro-mechanical strain-gauge sensor made from a sandwich of polyamide and platinum that runs around the circumference of the lens. When the strain gauge bends following a change in the pressure of the cornea, it stretches, and the change in its resistance is then measured by a custom-built, application-specific integrated circuit, which then encodes and transmits the data via an antenna to the receiver around the eye.

A circular antenna taped around the eye not only powers the electronic components in the contact lens, but also acts to receive the data from the lens

Because the lens is powered via the received radio waves, it does not need to be connected to a battery and the embedded components are positioned in the lens in such a way that they do not interfere with the patient’s vision. The lens is fitted by the ophthalmologist and when the patient returns the next day the ophthalmologist removes the lens and receiver, obtaining a complete record of IOP changes over the preceding 24 hours.

Although the new system does not measure the pressure of the cornea directly, it does monitor pressure fluctuations. According to Leonardi, this is a key parameter for ophthalmologists who are concerned about how pressure fluctuates in a patient suffering from glaucoma. The system allows them to determine how many pressure peaks occur and how long they last. Armed with this knowledge, they can make the proper diagnosis and provide more personalised medication.

Moreover, since the doctor will always take an IOP measurement at the beginning and at the end of the 24-hour monitoring session with the usual tonometer, he or she will always know the initial and final pressures in the eye, which can then be related to the data obtained from Triggerfish.

The Sensimed Triggerfish, which has already obtained the CE mark, is undergoing trials and is commercially available in selected parts of the world. ’The device is easy to use and has facilitated and improved patient care substantially,’ claimed Dr Kaweh Mansouri, who has been using the Triggerfish at the University Hospital in Geneva.

The key facts to take away from this article

» Glaucoma is often only diagnosed after nerve damage has occurred
» Infrequent measurement may fail to detect an elevated IOP
» Triggerfish monitors IOP continuously over a period of 24 hours
» The system can enhance diagnosis and enable more suitable treatment