More than three million Americans are currently living with glaucoma, an eye disorder with few symptoms in its early stages. Globally, the number may increase to almost 80 million by 2020, according to the British Journal of Ophthalmology. Glaucoma eventually leads to damage of the optic nerve.
University of Washington engineers have developed a new sensor to continuously monitor for the disease. By fitting the sensor into an intraocular lens implant during cataract surgery, the device could detect pressure changes instantaneously and transmit the data using radio frequency waves.
Nerea Alayo, Postdoctoral Research Associate at the University of Washington, currently leads the effort of the second-generation intraocular pressure (IOP) sensor development, which will include wireless communication and a simpler design.
Sensor Technology: Describe your glaucoma sensor.
Nerea Alayo: The sensor is an intraocular implant that measures the pressure inside the eye. Eye pressure fluctuations can result in glaucoma disease. The main difficulty in detecting glaucoma is that the first symptoms are undetectable; it is very important to detect glaucoma in its early stages, before irreversible nerve damage occurs.
Nowadays, Goldmann tonometry [a technology that uses a contact prism, contact probe, and calibrated measuring drum] is normally used to measure the eye pressure. Since this procedure requires a visit to the doctor, the intraocular pressure measurements are generally taken with intervals of several months or a year. To really detect glaucoma, more frequent measurements, like 24-hour monitoring, are needed.
Sensor Technology: How does the technology work? How is it embedded in the eye?
Alayo: This is a passive sensor that measures the intraocular pressure, using a capacitive sensor, and sends the data wirelessly to an external readout. The sensor is implanted in the eye using the well-established cataract implant design and surgery procedures. These polymeric cataract lenses are implanted through a two- or three-millimeter incision in a suture-less surgery. The standard cataract lenses are rolled so they can be introduced in the eye using a needle. Once the lenses are inside, they expand, recovering their original shape. Three-million cataract surgeries are done every year in the US; it is a well-known five-minute surgery.
To take advantage of the simple cataract surgery procedure, the intraocular pressure sensor will be embedded in these lenses. Therefore, our device needs to have the same mechanical characteristics; it needs to be flexible and stable, even after rolling. Since we have a wireless sensor, and external communication is needed, the design of the device includes an antenna, which is the most critical point when it comes to rolling the device. To maintain the mechanical properties of the sensor, we are using flexible, biocompatible materials that allow a metallic antenna to be incorporated.
Sensor Technology: You mentioned external communication. How is that data communicated?
Alayo: Since this work hasn’t been published yet, I can’t talk too much about technical details. But our final goal is to have data communication between the intraocular sensor and the external device. It will probably be possible to use an adapter attached to a smartphone. So you will just need to put your smartphone close to your eye to measure the intraocular pressure. Then, this data can be directly sent to the physicians, without a visit to the hospital. It may be that the pressure could even be measured during the night, having the smartphone by the bed.
Sensor Technology: What kinds of materials allow that flexibility?
Alayo: For the first prototype, polydimethylsiloxane (PDMS) was used. Now we are moving to more biocompatible and easier-to-manufacture materials. These materials can be processed at large scale using standard microelectronics fabrication techniques.
Sensor Technology: Does the sensor only detect pressure? What else can it detect?
Alayo: Right now, we’re focusing only on measuring pressure. We want to use this as the first proof of concept. Then, we can use this technology for other applications.
Sensor Technology: What other electronics are being put into the lens of the eye?
Alayo: Implanted devices need to last inside the body for about 50 years, so hazardous materials, batteries, or integrated circuits should be avoided. For these reasons, in the new generation of our device, we want to get rid of these elements and create a completely passive device.
Sensor Technology: What are the challenges of implementing this type of technology in a mainstream way?
Alayo: First, we need to use very biocompatible, reliable materials that will last inside the body for a long time. They need to be flexible, and be fabricated at a larger scale. At the same time, as the space inside the eye is very limited, this device needs to have reduced dimensions. And, as mentioned, we don’t want to place any electronics inside the eye, so we are developing a way to have wireless communication with the outside world, housing all the electronics in the external device.
Sensor Technology: What are you working on now?
Alayo: In this second-gen device, we are still working on the fabrication. Very soon, we will start testing the trans mission and communications cap - abilities.
Sensor Technology: Why do you think this is a valuable way to address eye diseases like glaucoma?
Alayo: This permanent implant is able to monitor intraocular pressure — 24 hours a day for many years, from your place, without the necessity to visit the doctor. Of course, then the data needs to be sent and evaluated by a professional. This implant is embedded on well-established artificial lenses and introduced using the cataract surgery technique that doesn’t require sutures. In addition, this is a passive sensor, without complex electronics on the implant. Thanks to this simplicity, it will provide the reliability required by implantable devices.
For more information about the University of Washington’s IOP sensor, visit http://www.washington.edu .