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    Biosensors in contact lenses can monitor IOP and diabetes

    Work is progressing on contact lenses that can monitor biomarkers in tear film for intraocular pressure (IOP), diabetes mellitus, and other health conditions.

    “Assuming that the technology performs as intended, the widespread use of contact lens sensors could provide a paradigm shift in clinical management of a variety of diseases,” wrote Chau-Minh Phan and colleagues of the Centre for Contact Lens Research, School of Optometery and Vision Science, Waterloo, Canada in Optometry and Vision Science.

    Related: Continuous IOP monitoring: Tools for addressing an unmet need

    Although the investment of Alphabet (the parent company of Google) in the technology has attracted headlines, multiple other companies are working on competing versions. Yet none has completely overcome the significant technical and clinical barriers to widespread use.

    Because IOP can fluctuate during the course of a day, the gold standard for its measurement, Goldmann applanation tonometry, gives an incomplete picture. Measurement position can also influence results.

    In 2009, Sensimed (Lausanne, Switzerland) launched the Triggerfish IOP-monitoring contact lens to address this challenge, the authors wrote. The device won approval from Conformité Européene in 2010 for commercialisation in Europe, but so far has not attained approval from the US Food and Drug Administration.

    It uses four circular strain gauges capable of sensing circumferential changes at the limbus, Phan and colleagues reported. Relative variations in IOP show up as a result of changes in ocular volume, they said.

    An embedded microprocessor and antenna in the contact lens sensor transfer the data wirelessly to an external eyepiece, and the data are stored on a portable unit worn on the waist or neck.

    In clinical trials, the results proved highly reproducible, and because no force is needed on the cornea, they are independent of the investigator and patient, the authors said.

    More: Why choosing the right multifocal IOL patients is important

    However, validation between the contact lens sensor and tonometry has proved difficult because of the impossibility of simultaneous measurement using the contact lens sensor and tonometry on the same eye.

    In addition, the eyepiece as currently designed is “both crude in appearance and large,” wrote Phan and colleagues. And the contact lens is larger with a higher modulus than a typical soft contact lens, making it relatively uncomfortable.

    However, the Triggerfish might prove useful for use over the course of 24 hours to glean information about fluctuation in IOP, with this information coupled to conventional measurements, they reported.

    Monitoring for diabetes

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