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The first in vivo tests of a wireless, soft contact lens sensor demonstrate that the device's measurements correspond with those taken via Goldmann tonometry. The contact lens sensor, which is designed to detect the tiny changes in corneo-scleral curvature induced by IOP changes, could be used potentially to monitor a patient's IOP changes over 24 hours.
Lausanne, Switzerland-Controlling IOP is crucial to the management of glaucoma. Yet, even the most diligent ophthalmologist may only see a patient with glaucoma and measure his or her IOP a few times each year. In addition, many ophthalmologists are concerned about diurnal, circadian, and inter-visit IOP fluctuations.
There is hope in new technology, however. The first in vivo results from a wireless, soft contact lens sensor designed to monitor IOP fluctuations show that the device may offer a solution by allowing for continuous monitoring of patients' IOP.
"Good control of IOP and its fluctuation is critical in glaucoma. In fact, the patient's prognosis may depend on it," said Elie Pitchon, MD, MSc, Jules Gonin Eye Hospital, Lausanne, Switzerland.
The CLS is a wireless, soft silicone contact lens with an embedded sensor to detect the tiny changes in corneo-scleral curvature induced by IOP changes.
According to Dr. Pitchon, the lens is the result of a joint effort between Jules Gonin Eye Hospital, the Swiss Institute of Technology, and Sensimed AG.
The active gauges are 7 μm thick. The lens also has passive gauges for thermal compensation, a microchip for signal processing, and a transmission antenna. There are no batteries; the lens receives its energy from an external loop antenna and transmits data wirelessly back to the same antenna. Data are stored on a portable unit and analyzed on a computer.
In tests on ex vivo, cannulated pig eyes, the signal from the strain gauges of the lens was found to be highly correlated with imposed IOP changes over a range of 3 mm Hg (11 to 14 mm Hg). The correlation was linear up to 30 mm Hg.
More recently, Dr. Pitchon and his colleagues conducted their first in vivo measurement. As in the pig eyes, the signal was highly correlated with IOP changes, in this case as measured by Goldmann tonometry.
The signal was filtered for blink suppression and averaging.
"Blinking induces a big change in the measurement of the contact lens sensor, but that peak is so short that you can filter it very easily," Dr. Pitchon said.
The biomechanical structure of the eye may be different for each patient, and, therefore, the IOP measurements and fluctuations could differ between patients, he said.
"An important thing for us, as ophthalmologists, is to know when the peak is occurring in our patients," he said. "With these data, you will know that timing precisely, even though the absolute measurement may need to be adjusted from one person to another."
Following the encouraging initial in vivo results, the next steps for the lens are to continue the clinical tests with a longer wearing period and to characterize the signal sensitivity.
"This device permits non-invasive, continuous IOP monitoring on humans, thus opening a new diagnostic and therapeutic approach to [the management of] glaucoma," Dr. Pitchon said. "This device potentially can be suited to monitor IOP fluctuations in humans continuously for 24 hours or more. Improving our knowledge of IOP fluctuations allows us better control [of] the disease."