German researchers developing implantable IOP monitor

Chicago-A consortium of German researchers is making considerable progress toward development of an implantable device for 24-hour monitoring of IOP, according to Peter Walter, MD.

The Acri.Sensor mesograph system, being developed by a partnership of industry, government, and academic groups, is a foldable IOL with integrated pressure sensors for the continuous measurement of IOP and wireless data delivery in a pair of glasses.

During a presentation at the glaucoma subspecialty day program at the American Academy of Ophthalmology meeting, Dr. Walter said that the developers were "close but not there yet" with their design. The working principle of the device has been proven in animal experiments, but further improvements in the stability of the system are necessary before it could be implanted in humans, he added.

"The main problem is the encapsulation, which is crucial to ensure long-term stability and function," said Dr. Walter, professor of ophthalmology, RWTH Aachen University, Aachen, Germany. "With a simple silicone encapsulation, water vapor will enter the device and cause electrical problems."

Currently, new prototypes are being developed for animal testing, with human trials possible in late 2006 or 2007 after successful testing of the modified devices, he added.

Partners involved in the Intraocular Pressure Sensor (IOPS) research project have worked for about 10 years to develop an IOL with an integrated microsystem that measures IOP, converts the data from analog to digital format, and transmits data to a reading station integrated into a pair of spectacles. The data-receiving station also provides the energy to power the microchip by high-frequency coupling.

The foldable implant can be inserted through a relatively small corneal incision, and in a series of rabbit experiments it was demonstrated that neither the implant nor the energy transfer was harmful to the eye, Dr. Walter said.

Researchers also observed the same amount of posterior capsular opacification in rabbit eyes with the experimental device implanted as in eyes that received an inactive electrical dummy device.

The system took 40 measurements per second with a high temporal resolution that allowed correlation of the IOP curve with the heart cycle, but calibration experiments and comparisons with other methods of IOP determination suggested that stability needed improvement.

"We don't know if the fluctuations are due to technology or whether this is due to the physiologic situation," Dr. Walter said. "Some of the sensors worked very well and others did not."

Ideal monitor

According to Dr. Walter, the ideal IOP monitor:

Several approaches to IOP monitoring have been discussed, including self-tonometry and devices such as smart contact lenses that would take IOP readings from the corneal surface. The most promising approach, tested by several other research groups as well as IOPS, seems to be the fabrication of an encapsulated pressure sensor with telemetric data and energy transfer and its integration into an IOL, Dr. Walter said.