Goldmann-Tonometry is still the gold standard of tonometry but it does not facilitate continuous pressure measurement. As intraocular pressure changes with activities and circadian rhythm, a snapshot measurement can miss pressure variations and spikes occurring during the daily course. As much as 80% of IOP peaks happen outside of scheduled appointments and frequently occur at night.1 In recent years, contact lens-based IOP sensors have emerged. The possibility to integrate pressure measurement and therapy into a feedback-loop has been explored in other diseases, like diabetes mellitus, where novel devices measure glucose levels and apply insulin as needed,2 which leads to a better disease control.
While most of the existing contact lens based applications for glaucoma focus on either sensing or delivery separately, the study by Yang et al. presents a wireless theranostic contact lens, which is able to continuously measure intraocular pressure and to deliver anti-glaucoma drugs as needed. The word 'theranostic' is a combination of 'therapeutics' and 'diagnostics'. As the space on a contact lens is curved and very limited the integration of a sensor and a delivery module is challenging. Increasing intraocular pressure leads to a deformation of the corneal curvature, which is transduced to the sensor circuit of the contact lens interfaced with the cornea. The displacement of capacitive plates induces significant electrical signals. If the pressure reaches a certain threshold an electric field is built up, which leads to a migration of positively charged brimonidine through the cornea into the anterior chamber ‐ a mechanism that is called iontophoresis. The sensory and the delivery module were tested ex vivo, using porcine eyeballs. The intraocular pressure was increased from 5 to 50 mmHg by controlled infusion of saline solution and the resonance frequency of the integrated reading coil was recorded. The relation between intraocular pressure and resonance frequency was analyzed. In vivo experiments were conducted on rabbits in order to determine the pressure lowering effects via iontophoresis. The power for the iontophoresis was applied by a wireless power transfer circuit.
The technology has to be significantly improved before human use as a sensing error of more than 40% has been mentioned
The wireless theranostic contact lens enables measurements of intraocular pressure and on-demand medicine administration without causing vision blockage. Separation of frequencies enables to have both pressure measurement and drug delivery on the same contact lens without cross-coupling. Still, the technology has to be significantly improved before human use as a sensing error of more than 40% has been mentioned. The paper describes the proof of concept of a promising new technology, but we have to see if it can be further developed for human trials.