Editors Selection IGR 21-2

Clinical Examination Methods: 24-hour IOP monitoring

Crawford Downs

Comment by Crawford Downs on:

86572 Highly Transparent and Sensitive Graphene Sensors for Continuous and Non-invasive Intraocular Pressure Monitoring, Xu J; Cui T; Hirtz T et al., ACS applied materials & interfaces, 2020; 12: 18375-18384

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IOP is incredibly dynamic, and recent evidence suggests that transient IOP fluctuations comprise 10-15% of the IOP-related mechanical energy that the eye must absorb during waking hours. IOP is a principal risk factor for glaucoma, and yet we know relatively little about which aspects of IOP dynamics drive glaucomatous pathophysiology. This gap in knowledge stems primarily from the lack of continuous IOP measurement technologies in human patients. One of the current commercially available IOP sensors are based on contact lenses that measure the circumlimbal stretch (strain) in the cornea to estimate the IOP change in the eye. These sensors read in arbitrary units and cannot be calibrated to an individual's IOP, which limits their use to detecting when a patient's IOP is high or low, although they cannot discern the magnitude of the IOP change. In the present study, Xu and colleagues describe a new graphene based strain gauge system that would purportedly improve the resolution and sensitivity of contact lens-based 'IOP' telemetry systems, and also possibly decrease measurement drift over time.

Corneal strain based systems cannot be calibrated to true IOP and so do not measure IOP directly.

They test the new sensor in a contact lens placed on a mock silicone model of the eye, and vary pressure in the mock eye at rates up to 0.8 mmHg/s. The new sensor was linear with pressure increase, performed well in tracking pressure variations up to 0.8 mmHg/s, and was stable over a 3-month testing interval. Further testing will be required to determine if the new sensor is capable of tracking strain changes at faster rates typical of OPA (~3 mmHg/s) or blink and saccade (up to ~40 mmHg/s). Integration of this improved sensor into current contact lens telemetry systems could improve measurement accuracy and performance. That said, corneal strain based systems cannot be calibrated to true IOP and so do not measure IOP directly. Hence, their utility in glaucoma management is limited and improvements to that approach are also limited.

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