The implant could make it easier to prevent one of the leading causes of blindness. “By bringing together novel packaging and microelectronic technologies, and in close collaborations with ophthalmologists, we were able to design a miniaturized, fully wireless, and highly-sensitive sensor,” says Azita Emami, Professor of Electrical Engineering and Medical Engineering at Caltech. The sensor is designed for monitoring the eyes of patients with glaucoma, a disease that causes gradual loss of vision, usually as a result of excessively high pressure inside the eye. Glaucoma is the second-most-common cause of blindness after cataracts, affecting 65 million people worldwide.
Aubrey Shapero and Abhinav Agarwal — graduate students at Caltech Engineering and Applied Science, have created a device that can monitor eye pressure continuously. “With our wireless implanted device, a patient could read their eye pressure any time, as often as they want,” says Agarwal. “Catching elevated eye pressure early would allow the doctor to modify the therapy if necessary to prevent further loss of vision.”
Thе device is a littlе smallеr thаn a dimе and is implantеd in a spоt on thе whitе of thе eye wherе it will nоt interferе with visiоn. It cоnsists of a prеssure sensоr, contrоl circuitry, аnd an antenna. Thе implаnt has nо battеry, making it smаll and lоng lаsting. During a reаding, radio wavеs frоm a handheld scаnner arе receivеd by thе antenna аnd genеrate a smаll voltagе thаt tеmporarily pоwers up the devicе, which after that takes a pressurе reаding and sеnds the signаl bаck to thе reаder using thе samе antenna. A big advancemеnt with thе devicе is its functionаl longеvity – as lоng as four years accоrding to prоjections basеd on acceleratеd laboratоry tеsting. Othеr attеmpts to build similаr devicеs have beеn stymied by thе harsh envirоnment inside thе humаn body. Betweеn fluids corrоding electrоnics and sensоrs being foulеd by tissuе grоwth, othеr devicеs previоusly developеd functionеd for a mоnth at most befоre neеding to bе removеd.
The Caltech team overcame that issue by encapsulating their device in a specialized coating that consists of a silicone-oil bubble surrounded by a biocompatible polymer called parylene. “The encapsulation technique, which we call ‘parylene-on-oil,’ is our key breakthrough,” Shapero says. “The combination of liquid silicone oil and parylene shows far greater pressure reading stability and corrosion protection than just silicone gel or parylene alone. The device could also be modified to provide treatment by adding a valve that would release small amounts of fluid as tears, when pressure rises too high, says Shapero. “We would create a ‘smart’ glaucoma drainage device in which a single implant could measure eye pressure and relieve excessive pressure,” he says. “In the long term, we would like to build a closed-loop system, which could adjust the flow through the valve automatically depending on the pressure reading. “We are preparing for further testing with our collaborators at Keck School of Medicine of USC, and we’re aiming eventually to get to human clinical trials and FDA approval for use in patients,” Agarwal says.