Medical Device Daily Contributing Writer

Glaucoma, a leading cause of blindness, is estimated by the World Health Organization (Geneva, Switzerland) to affect 70 million people worldwide. Although increased intraocular pressure has long been recognized as its leading cause, this pressure has proven elusive to measure accurately. Indeed, it can vary widely over the course of the day, and may escape detection.

There is growing consensus among students of the phenomenon that intraocular pressure rises at night, where it could wreak maximum havoc. A body of evidence from circadian studies on animal models supports this belief; pressures measured in the light phase were significantly lower than those in the dark phase. However, the situation in humans is complex, and both higher and lower nocturnal pressures have been observed.

A Swiss start-up company, Sensimed (Lausanne), has developed a novel technology for addressing this problem, according to Dr. Matteo Leonardi, founder/chief technical officer. The device consists of a soft disposable contact lens with a micro electromechanical sensor embedded in it, which allows the measurement of corneal deformation due to intraocular pressure. The placement is non-invasive, the lens is simply inserted over the eye as would be a standard contact lens. A telemetry microprocessor and an antenna are also embedded into the contact lens sensor for wireless power and data transfer.

The other innovative component of the system is the means of collecting and storing data. This is handled by the contact lens sensor system, which consists of a pair of glasses and a pocket reader. Signals from the sensor are detected by the glasses and data are retrieved wirelessly and stored in the pocket unit. The system allows 24-hour continuous intraocular pressure monitoring, during which time the patient's movements are unrestricted.

Screening for glaucoma is currently performed by measurements of the intraocular pressure via tonometry, a procedure by which the amount of pressure required to flatten a certain portion of the eye is measured, using a tonometer. This standard procedure may be augmented with a pachymetry to measure the cornea thickness, as this can influence the accuracy of the pressure measurements.

Another feature of the pathogenesis of glaucoma is the role of ocular blood flow. There is increasing evidence that ocular blood flow is involved in glaucomatous optic neuropathy and that unstable blood pressure and dips are linked to optic nerve head damage. These facts further support the utility of the Sensimed technology.

While the device was developed with its clinical applications the foremost goal, there is a wealth of anecdotal information as well as examples from the literature that indicate strong interest on the part of the research community. Eye researchers interviewed for this story waxed euphoric concerning its possibilities for studies on both clinical and animal models.

According to ophthalmologist Dr. Douglas Gregory, "I would also guess that researchers would drool over the prospect of getting hold of these devices." Frank Liang, MD, PhD, an ophthalmologist and associate director for in vivo studies at Advanced Vision Therapies, said, "Given the fact of circadian changes in intraocular pressure, continuous monitoring by this noninvasive device would greatly facilitate the diagnosis and treatment of glaucoma disease by providing a comprehensive data set throughout day and night."

A number of published studies demonstrate the potential applications of the Sensimed technology. These include investigations of the effects of the drugs brinzolamide and timolol during the diurnal period. Clearly a convenient method of measuring intraocular pressure during this time frame would be of great value, allowing a range of the different conditions and combinations to be evaluated.

A related study investigated the performance of currently available ocular hypotensive medicines over a 24 hour time frame in patients with primary open-angle glaucoma. Because these studies are usually performed during the daytime for reasons of convenience and economy, the information gathered may be inadequate for making optimal clinical decisions.

Separate studies revealed that pressure measurements taken outside the normal office hours change the peak pressure assessment in 69% to 75% of cases. Finally, it has been shown that mean peak pressure rose when measured when measured outside normal office hours.

The combination of its promise as a research tool combined with applications in the clinic make the Sensimed technology doubly appealing. The contact lens could be easily modified to fit a rabbit, a common candidate for these experimental designs. This would open the possibility of the sort of studies that Liang suggests, without the necessity of 3 a.m. visits to the laboratory on the part of exhausted researchers (or more likely their technicians).

The only drawback to the development of a research application of the monitoring system is the availability of funding. According to Sensimed CEO Jean-Marc Wismer, "making a lens for rabbits will require a change in the lens (smaller diameter) together with some minor electronic adaptations. In principle it can be done fairly easily, but the budget associated for the necessary R&D would be in the range of $200,000, so we have not pursued this route."

Finally the device appears somewhat cumbersome, but with the operation of "Moore's Law" (the observation that every 18 months the size of computers is cut in half and their capacity doubles) there can be little doubt that the device will become increasingly miniaturized and user-friendly.