Continuous 24 h monitoring of changes in intraocular pressure with the wireless contact lens sensor Triggerfish™. First results in patients

Background. For many years researchers have been striving for a non-invasive 24 h continuous method of ambulatory intraocular pressure monitoring. A wireless device with a contact lens sensor is now on the market for clinical use, which is not a quantitative measurement of the intraocular pressure but is at least a recording of qualitative changes. These changes of corneal curvature due to changes of the intraocular pressure result in a distinct profile which gives information about fluctuations of the intraocular pressure, the behaviour during supine sleeping time and the 24 h efficacy of glaucoma therapy. We investigated the practicability and tolerability of this device. Method. The sensor is embedded in a soft silicone contact lens and consists of 4 strain gauges. Additionally there is an antenna made out of gold and a microchip. A second antenna is fixed around the eye which sends impulses to the microchip and receives data from the microchip. The data are sent to a recorder via a wire. Measurements are made for 90 s every 8.5 min resulting in 144 measurements within 24 h. Of the 4 strain gauges 2 sense changes in the corneal curvature due to changes of the intraocular pressure. This device was used in 11 patients with ocular hypertension or glaucoma. Results. The result of the 24 h continuous measurement is a pressure profile which may be flat, fluctuating and with no, some or many spikes. We describe 2 examples of profiles from patients with glaucoma. The changes in the profiles were mostly during the sleeping hours in a supine position. Due to the lack of validation of the results it is not known if intermittent spikes are true spikes or artefacts. Practicability was simple and tolerability was reported to be good by all patients. Conclusions. For the first time a practicable, well tolerated, non-invasive device for continuous 24 h monitoring of changes of the corneal curvature due to changes of the intraocular pressure is available. It is not a direct measurement of the intraocular pressure. The resulting profile gives additional information about the behaviour of the intraocular pressure, especially during out-of-office times and night times. Disadvantages are the high cost of the contact lens sensor and the lack of validation of the results and reproducibility in patients.