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Editors Selection IGR 11-2

Intraocular Pressure: Wireless contact lens sensor

Comment by John Liu on:

23776 Wireless contact lens sensor for intraocular pressure monitoring: assessment on enucleated pig eyes, Leonardi M; Pitchon EM; Bertsch A et al., Acta Ophthalmologica, 2009; 87: 433-437

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Elevated intraocular pressure (IOP) is a major risk factor for glaucoma, a 24/7 disease. However, clinical IOP assessment for glaucoma diagnosis and treatment is severely restricted by time and by the technical requirements of a measuring device. It is desirable to have a sensor for continuous IOP monitoring in glaucoma patients, in glaucoma suspects, and in many ocular hypertension patients. There are two potential types of continuous IOP sensors: non-invasive temporary IOP sensors and implantable permanent IOP sensors. There has been significant progress in both types of IOP sensors in recent years, with each type having its own advantages and disadvantages. In 2004, Leonardi et al. (615) described a non-invasive IOP sensor using a silicone contact lens with an embedded strain gauge which determined IOP based on the change of corneal curvature. Their proof of concept model included a contact lens sitting on an enucleated pig eye, with an external wire to a power source and electronics for data communication. In the present follow-up study, Leonardi et al. (615) took another important step by embedding a telemetry microprocessor inside the contact lens. Both power charging and data communication for the microprocessor were wireless. This wireless contact lens IOP sensor performed equally well on the enucleated pig eye. Obviously, patients will accept a wireless contact lens IOP sensor more readily than a wired contact lens IOP sensor; this is an essential consideration for a clinical trial. As the authors discussed in the article, future clinical trials may face issues that have not been encountered during the laboratory testing. Physiologic factors, such as eye movement, blinking, tear film dynamics, contact lens shifting, and closed eyelids during sleep may all affect the accuracy and reliability of this wireless IOP sensor. Some data noise may be easily overcome by employing software, but handling other factors may require additional research. Issues related to the contact lens material may also appear. For the current design, silicone was chosen in order to reduce the contact lens hydration pressure and to improve the sensitivity of strain gauge. Will the corneal response to a silicone contact lens significantly alter the sensitivity and accuracy of this IOP sensor? We look forward to learning more from the upcoming clinical trial. For now, the authors should be commended for their efforts to bring the dream of a continuous IOP sensor closer to reality.

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