Diagnostic Contacts

A contact lens that tracks ocular pressure may help treat glaucoma

There is no cure for glaucoma, which affects around 65 million people worldwide and is the second-most common cause of blindness in developed countries. Even with vigilant monitoring, drugs, and surgery, some patients go on to lose their sight. For these patients, hope could come in the form of a gold-ringed contact lens.

The lens, made by Swiss medical-device company Sensimed, picks up slight changes in fluid pressure inside the eye and beams the data to a palm-size recorder. It’s been approved for use in Europe and is being tried on about 100 glaucoma patients in six research centers in Austria, Germany, and Switzerland.

Sensimed CEO Jean-Marc Wismer says the lens should make it easy to monitor eye pressure over an entire day. He adds that previous studies on glaucoma patients have shown that in about 80 percent of cases, such monitoring allows doctors to improve treatment, either by refining the patient’s drug regimen or recommending surgery earlier.

”This device has the potential to revolutionize glaucoma care,” says Kaweh Mansouri, an ophthalmologist who has used the system on 15 patients at the University Hospitals of Geneva. He adds that it could do as much for glaucoma patients as home-based 24-hour blood-sugar monitoring has done for diabetes patients.

Tracking internal eyeball pressure is critical to predicting the outcome of glaucoma. High pressure from excessive fluid buildup inside the eye is thought to be the main reason glaucoma causes vision loss. Blindness seems to result when a buildup of fluid in the eye raises the pressure enough to damage the optic nerve. Eye doctors measure intraocular pressure periodically with an instrument called a tonometer. But these occasional in-office tests can easily miss the full picture.

”There are some people that have glaucoma but don’t have high pressure, or maybe they have high pressure but not when they come in, and we do that instantaneous measure,” says Charles Leahy, an optometrist at the Massachusetts Eye & Ear Infirmary. And ”you don’t know if their pressure spikes at night.” The new contact lens monitoring system provides more meaningful data, he says.

Patients have a circular antenna taped around the eye and connected to a battery-powered portable recorder that can be carried in a pocket or worn around the neck. The antenna transmits radio frequency energy to an ultrathin gold ring—itself an antenna—that’s on the lens. The RF energy powers a tiny chip embedded in the lens. Also on the lens is a thin platinum ring that stretches, changing its resistance, as the eyeball inflates slightly from its internal pressure. The microprocessor measures this change and sends the data back to the recorder.

The setup might sound cumbersome to wear and sleep with for 24 hours, but so far the roughly hundred patients who have tried the system wore it eagerly. These are people ”who are getting blind despite treatment; they’re extremely motivated to stop losing vision,” Wismer says. And the alternative monitoring scheme is rather unpleasant—spending the night in a sleep lab and being awakened every few hours for measurement.

The lens is already being distributed in Europe, and Sensimed hopes to get regulatory approval in the United States by late 2011. For now, the lens is being used to monitor only diagnosed patients, but Wismer says it could someday be part of routine diagnostic testing of people who have a family history of the disease or show abnormal pressure readings. Drug developers could also use the system to evaluate the effectiveness of new medicines.

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