Glaucoma Test in a Contact Lens
Glaucoma is the second most common cause of blindness, and without constant vigilance it can prove a very difficult disease to manage. But a Swiss biotech company has developed a monitoring system that allows physicians to keep track of their patients’ symptoms over 24 hours. Sensimed’s “Triggerfish” system consists of a contact lens with embedded sensors that can pick up subtle physical changes in a patient’s eye, and then wirelessly transmit that data to a receiver worn around his neck.
Despite decades of study, researchers still only poorly understand the causes of glaucoma, a group of diseases in which deterioration of the optic nerve can eventually lead to blindness. But controlling one symptom in particular–high intraocular pressure, which is caused by too much liquid inside the eye–appears to help prevent disease progression.
“Nowadays, glaucoma specialists live in the dark,” says Kaweh Mansouri, an ophthalmologist who has been using the Sensimed system in his clinic at the University Hospital, Geneva. “We only get a few chances to see the patient and measure intraocular pressure, and we know this is a major drawback of how we diagnose and treat glaucoma.”
Current methods for glaucoma diagnosis and monitoring are usually limited to single snapshots in time, taken at a visit to the eye doctor during daytime, when pressure tends to be at its lowest. But glaucoma specialists believe that one of the main contributors to disease progression is frequent changes in pressure over the course of a day, or high peaks during the night–something that, in the most serious cases, requires frequent measurement during an overnight hospitalization. The Sensimed device, the first of its kind on the market, provides constant readings for a fraction of the price of a hospital stay. The company received safety approval for Triggerfish in Europe last year, and is hoping for U.S. Food and Drug Administration approval by late 2011.
The Triggerfish lens is made of the same silicon hydrogel as many of the soft contact lenses currently on the market, but embedded within it is a microprocessor and a strain gauge that encircles its outer edge. When fluid accumulates in the eye, the diameter of the cornea changes, and that change is picked up by the strain gauge. Data is processed and then transmitted via radio frequency to a receiver.
In more than one-third of the 50 patients Mansouri has tested, the results led to a direct, immediate change in treatment, he says. If a person’s intraocular pressure peaked at odd hours of the night, for example, he could now detect it and change medication doses to account for that. If prescription drugs didn’t seem to be helping at all, he could change course and try surgery instead. “For the first time, we were able to look into the darkness of glaucoma, and we saw things happening during the night that were surprising,” he says.
Ultimately, Sensimed believes it may be possible to use Triggerfish to detect glaucoma at earlier stages in people with a family history of the disease or other risk factors. If a high-risk patient has a relatively normal daytime pressure, says company president and CEO Jean-MarcWismer, he might benefit from a preventative 24-hour monitoring session every once in a while. “We would like to be able to diagnose glaucoma earlier, before it actually causes damage that affects vision.”
This may be a bit premature, says Andrew Iwach, the executive director of the Glaucoma Center of San Francisco. “Some patients have high intraocular pressure, but their optic nerve tends to do fine. Others have lower pressure, but still have a major impact on their optic nerve,” says Iwach, who’s also spokesperson for the American Academy of Ophthalmology. The problem, experts say, is that increased intraocular pressure is the only symptom of glaucoma that is treatable and can slow or stop disease progression.
However, both Iwach and Stanford ophthalmology professor Kuldev Singh believe that continuous monitoring of intraocular pressure is something the field desperately needs, and note that there are multiple groups working toward such a goal. But while the new device will likely have a major benefit in understanding individual patients’ treatments, Singh says, it also provides an important opportunity to better understand the disease. “The idea of a continuous measurement device for eye pressure is a very, very good one,” he says. “I think the most important use for it is to better study the relationship between eye pressure and glaucoma progression.”
“From a scientific standpoint, this type of technology will be groundbreaking in letting us understand the relationship between eye pressure and glaucoma, and how treatments work over a 24-hour period,” says Singh, who is also chair of the Glaucoma Research Foundation’s board of directors.
To date, the device has only been used clinically in about 80 patients–the holdup, says Mansouri, is price: It’s not yet reimbursed by the Swiss health care system. Prices should drop, however, as reimbursement increases and production scales up.
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