EyeWorld is the official news magazine of the American Society of Cataract & Refractive Surgery.
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EW GLAUCOMA 88 October 2014 by Michelle Dalton EyeWorld Contributing Writer Continual IOP monitoring the first small case series on the wireless intraocular pressure transducer (known as WIT) look promising. 2 The WIT integrates "pressure sensors, temperature sensor, identi- fication encode , analog-to-digital encoder, and telemetry unit into a single microelectromechanical sys- tem application-specific integrated circuit," the study authors wrote, 2 although there are no plans to inte- grate the technology into an IOL. The WIT has been evaluated during phaco surgeries through a 4.5 mm incision, but Dr. Melki said a newer version of the device is "thinner and is currently undergo- ing trials in Europe." For now, the planned follow-up will be 2 years; the group is also planning to investi- gate the device in the U.S., primarily in patients with keratoprostheses. "The ultimate goal is to have this device available for glaucoma patients as well," he said. In one case study of a wom- an in her 60s who presented with primary open-angle glaucoma and cataract (maximal IOP at presenta- tion was 39 mmHg, and BCVA was 20/200), initial corneal edema and iritis developed but resolved within the first month. Although postop recovery was longer than typical for cataract surgery, Dr. Melki attributed the delay to the additional manipu- lation with the iris hooks needed in that particular case. Uncorrected VA Two groups of researchers are independently working on implantable devices to constantly measure IOP fluctuation A n implantable device that can continuously mea- sure IOP will reduce the number of patient visits and the number of fluct - ating readings, and will substantially reduce the cost of healthcare, say 2 groups of physicians working on similar devices. Currently, glaucoma specialists have to rely on readings from office visits to determine if medical therapy is managing the disease; the miniaturization trends in sensors and electronics may im- prove IOP monitoring by allowing patients to self-monitor, said Karl F. Böhringer, PhD, John M. Fluke distinguished chair, professor of engineering, University of Washing- ton, Seattle. His group is working to combine an IOP monitoring device and an IOL that would use low-pow- ered active circuits to monitor IOP fluctuations wirelessl . Still in the proof-of-concept phase, Tueng T. Shen, MD, PhD, professor of ophthalmology and bioengineer- ing, University of Washington, and director of the refractive surgery center, University of Washington Medical Center, said the full-sized device has proven in the lab that the science is solid. "In terms of biocompatibility, the materials we're evaluating are what's commercially available in IOLs; both silicone and acrylic can be adapted for use with the device," she said. The device would be placed in an artificial lens with its antenna circling the perimeter and the sensor and radio frequency chip inside, Dr. Böhringer said. Engineers have for- mulated a method that allows these miniscule chips to process signals, convert them into radio waves, and send the data out to an external device for evaluation. "The device is designed to be embedded into a capsular tension ring (CTR)," Dr. Böhringer said. The ultimate goal, Dr. Shen said, "is to get a better handle on how patients' pressure has been doing to better manage glaucoma, with the theoretical goal of avoiding glaucoma surgery altogether." In theory, the device will help address whether or not medications are still effective when IOP is typically lower, during sleep. A recent paper 1 noted the device "shows promising results toward building a complete wireless IOP monitoring device," and Dr. Böhringer envisions a handheld re- ceiver will collect the data for trans- mission to the physician's office. "Right now, we have a large desktop contraption that signals with an antenna," he said, and while the current device is not ready for human trials, within the next 1–3 years, university engineers hope to have recreated the device using the CTR as its platform. "I anticipate in the next few years we'll try to demonstrate an IOL-compatible version to be used in relevant studies," Dr. Shen said. Dr. Böhringer believes it may be 5 years before human trials begin. "We want to push forward into the market eventually," Dr. Shen said. "The 'smart lens' will be the future so any lens that has elements that help us monitor temperature, pressure, any of those things will be beneficial for patients. Currently in studies Another similar device is already being evaluated in human subjects. Samir Melki, MD, PhD, Boston Eye Group, said results from A device for continuous intraocular pressure (IOP) monitoring has always been near the top of the wish list for glaucoma treatment. We currently capture just a small number of momentary IOPs each year on our glaucoma patients—sometimes just 2—and use them to extrapolate what the IOP is doing for the rest of the year. This huge leap of faith could be overcome if we had the technology to monitor IOP continuously. We are very fortunate to have Karl F. Böhringer, PhD, Tueng T. Shen, MD, PhD, and Samir Melki, MD, PhD, update us on the current status of these breakthrough devices. Continuous IOP monitoring might help us to figure out why some p tients' pressures may seem to be in good control but their glaucoma is still worsening. We currently have other narratives to explain this disconnect such as "normal tension" glaucoma, underestimating the true IOP because of a thin cornea, and poor compliance. But we also would like to know what the IOP is doing during the 99.9% of the time that we are not measuring it. Continuous monitoring could give us a much better understanding of whether we are reaching our treatment goals. Although there are numerous challenges to bringing this technology to our patients, it is clearly only a matter of time. The initial devices may be mainly research tools. However, with further miniaturization and other technical improvements, we expect that continuous IOP monitoring will be just one among many measurements available from "smart" IOLs—with readouts probably available on our phones. Reay H. Brown, MD, glaucoma editor Glaucoma editor's corner of the world The wireless intraocular pressure transducer (WIT) Source: Samir Melki, MD, PhD