December 2018


Device focus
24-hour IOP monitoring could enhance glaucoma outcomes

by Michelle Stephenson EyeWorld Contributing Writer

Triggerfish is currently the only device approved for 24-hour IOP monitoring

It is well-known that IOP variation contributes to glaucoma progression. Yet IOP is measured infrequently in stable glaucoma patients so it is difficult to tell if patients are having IOP variations with the current monitoring strategies. The desire to capture a more complete picture of a patient’s IOP over time has led to the development of 24-hour continuous IOP monitoring devices.
“The only device currently approved in the United States that allows for continuous IOP measurement is the Triggerfish contact lens from Sensimed [Lausanne, Switzerland],” said Malik Kahook, MD, University of Colorado, Denver. “However, this device utilizes a surrogate measurement based on the biomechanics of the cornea and not true IOP. It is listed on the FDA website as an ocular pattern recorder and is comprised of a hydrophilic, single-use soft contact lens with an embedded sensor and antenna that allows for continuous wireless recording of changes in ocular dimension. The system is coupled with an external adhesive antenna, placed around the eye, which is connected to a pocket-size recorder worn by the patient.”
Other companies have developed devices and are currently exploring FDA approval for continuous IOP monitoring. One example is Implandata’s (Hannover, Germany) sulcus fixated device that is implanted using an OR-based surgical procedure. “While the device is more invasive than the Triggerfish device, it is designed to allow for extended use over the lifetime of the patient rather than the single 24-hour measurement for which the Sensimed system is designed,” Dr. Kahook said. “It should be noted that neither one of these two devices is truly a continuous monitor, as they both collect a stream of data at given time intervals and are not always ‘on’ for data collection.”


From a safety standpoint, the Triggerfish device has a similar profile to soft contact lenses in general. “The main issue is with comfort due to the tight-fitting nature of the lens; however, we found this to be only of minor concern with most patients tolerating the use of the device well,” Dr. Kahook said.
The Implandata device carries with it all of the risks of an invasive ophthalmic surgical procedure, such as pain, bleeding, and possible infection. “It could theoretically have other issues, such as collateral tissue damage post-insertion; however, the device is micro-engineered to be atraumatically implanted and to remain safe for the lifetime of the patient. Neither device has long-term data in a wide range of patients for any real conclusions to be made on long-term safety,” Dr. Kahook said.

Wealth of data

According to Dr. Kahook, both devices will allow for collection of a wealth of IOP data. The Triggerfish device can collect data while the patient is sleeping, while the Implandata device, as far as is publicly disclosed, will likely first rely on patient (or caretaker) activation of the recording so that nighttime pressure checks will need to take place while the user is awake.
“Regardless, the hurdle to collecting, storing, and transmitting data to the physician is no longer an issue, and this technology is readily available in HIPAA-compliant form,” he said. “The big question is what to do with the data once they are received. I can imagine circumstances where the obtained data are within the target pressure for patients being treated for glaucoma, and this could be reassuring to both the patient and the doctor. However, there could be circumstances where obtained data reveal episodic IOP elevation while the patient is exercising or sleeping, and we are not equipped at this time to gauge the clinical relevance of episodic increases in IOP in these scenarios. Is it clinically relevant for a patient to have a few nighttime IOP spikes of 20 to 25 mm Hg when his or her goal IOP is 15 mm Hg? Do we change therapy based on these findings? With the Triggerfish device, these data are further complicated by the fact that the output data are not in mm Hg, but rather reveal changes from baseline that could be extrapolated to ‘real’ IOP. I am not sure we know enough to convert these biomechanical changes to actual IOP, and all of our therapeutic interventions are based on measurement of mm Hg at this time. One could envision that these data could be used to make therapeutic decisions when not appropriate and could lead to advancement of medical therapy, or even surgical therapy, when none would be needed. It is simply too soon to understand how these data can help drive therapeutic decisions,” he said.
Sameh Mosaed, MD, Irvine, California, agreed. “Most 24-hour IOP studies are being performed in sleep laboratories. This is currently not used for day-to-day patient care. These are research tools, and the research methodology involves admission to a sleep laboratory. These studies are controlled. The timing of the readings is controlled, and the medications the patients are taking, their fluid intake, and their blood pressure are monitored, measured, and controlled. This means that they are not necessarily representative of what would happen in daily life. Another concern with 24-hour IOP monitoring, in general, is that it provides a lot of information, including a lot of artifact, and it’s hard to know what to do with all of that information and how relevant each piece is,” she said.
Conversely, if a given patient appears to have well-controlled IOP at every clinic visit and yet is progressing despite what is perceived to be adequate therapy, 24-hour IOP data might lead to some clues that could help dramatically improve outcomes. “Perhaps the patient is not always taking his or her drops, and continuous monitoring will reveal non-adherence that is difficult to gauge from clinic visit interactions,” Dr. Kahook said. “Perhaps the patient has a large spike in IOP at night when sleeping, and changing the medical or surgical approach to care could lead to stabilizing these spikes over time. These are a couple of scenarios where I can see continuous monitoring leading to an enhancement of outcomes in a subgroup of patients.”
Dr. Mosaed agreed. “I think 24-hour IOP monitoring makes sense if a patient’s glaucoma seems to be getting worse despite what is considered controlled intraocular pressure in the office setting. This makes you wonder if he or she is having IOP spikes outside of office hours. Are patients having nocturnal IOP elevation? Do they have decreased perfusion pressure during the nocturnal period or some other explanation for why they would be getting worse? These are patients in whom it would make sense to do a sleep study,” she said.
She added that perfusion pressure is an important concept in these patients as well. “A lot of the information that we’re getting from 24-hour IOP studies relates not just to IOP but also to what happens to systemic blood pressure during the nocturnal period as it relates to IOP. Are some of these patients progressing because they have decreased perfusion pressure during the nocturnal or even diurnal periods? So, 24-hour IOP by itself as an isolated measure may not be as relevant as 24-hour perfusion pressure,” Dr. Mosaed said.
With regard to the future, Dr. Kahook thinks we are in the middle of a revolution in the surgical management of glaucoma utilizing microinvasive techniques with a favorable risk-benefit profile. “This has pushed surgical intervention into an earlier treatment modality for glaucoma patients, and obtaining more reliable data on adherence problems or lack of therapeutic efficacy from medications might help drive decision-making to earlier surgery with enhanced outcomes,” Dr. Kahook said.

Editors’ note: The physicians have no financial interests related to their comments.

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