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Devices for continuous IOP monitoring will address the need to better understand IOP levels and patterns in patients with glaucoma.
Take-home: Devices for continuous IOP monitoring will address the need to better understand IOP levels and patterns in patients with glaucoma.
Kaweh Mansouri, MDDenver, CO-The opportunity for practical and reliable 24-hour IOP measurements is one of the major unmet needs in glaucoma management. According to Kaweh Mansouri, MD, considerable progress has been made in recent years, and he is optimistic that the future will bring even better technology.
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Describing his “wish list” for a 24 hour IOP monitoring device, Dr. Mansouri said,” It should be inexpensive, safe, accurate, and obtain measurements with a high frequency (>40 Hz) so that ultrashort events can be detected. The jackpot, however, would be a device that could store and release IOP-lowering drugs on demand.”
“My prediction is that the next generation of ophthalmologists will see such a device, and they will take its use for granted similar to how we now do with OCT and intravitreal injections.”
The benefit of having a 24-hour IOP monitoring device lies in the fact that in-office measurements provide a mere snapshot of IOP.
“In a patient seen 3 to 4 times a year, we obtain about 12 seconds worth of IOP data. Realizing there are more than 31 million seconds in a year, we are not even looking at the tip of the iceberg when it comes to measuring IOP,” said Dr. Mansouri, consultant ophthalmologist, Glaucoma Center, Montchoisi Clinic, Lausanne, Switzerland, and adjoint associate professor of ophthalmology, University of Colorado, Denver.
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The paucity of in-office measurements means that clinicians miss fluctuations in IOP and also nocturnal values, which may be significant considering that peak IOP peak values in most people occur during the night.
“Thus, it is not surprising that axonal injury often occurs in patients whose IOPs are considered physiologically normal based on current approaches to measuring IOP,” Dr. Mansouri said.
Continuous monitoring solutions
Two devices for 24-hour IOP monitoring have been evaluated in clinical trials. One, which is not FDA-approved, has an implantable miniature sensor that is telemetrically powered (EyeMate, Implandata). The sensor, which measures 11.2 mm in diameter, is intended to be implanted in the ciliary sulcus during cataract surgery. It consists of eight pressure-sensitive capacitors and a circular microcoil antenna.
The most frequent adverse events reported so far with this device are iris chafing and pigment dispersion, raising the concern about the potential for IOP elevation secondary to increased outflow resistance, Dr. Mansouri said.
A recent clinical trial evaluating the device in six patients followed for 1 year showed that it detected changes in IOP induced by specific ocular manipulations. However, its measurements corresponded well with values obtained by tonometry only in some subjects, and there were also cases of substantial drift in accuracy over time so that device recalibration was needed.
“Nevertheless, I would say the data are encouraging, and we look forward to more studies evaluating this technology in larger populations,” Dr. Mansouri said.
The second device, which is commercially available in the United States and elsewhere (Triggerfish, Sensimed), is a contact lens-based system with a sensor that measures limbal strain. Its performance has been more widely investigated.
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“There is a plethora of data available attesting to the safety and reproducibility of this device and comparing it to tonometry,” Dr. Mansouri said.
For example, a study conducted by Dr. Mansouri and colleagues at the University of California San Diego showed that IOP measurements obtained with the contact lens-based system compared well with those obtained in the fellow eye by pneunotonometry with respect to IOP values and daily and nightly IOP patterns, including timing of peak IOP that occurred somewhere between 4 and 5 AM.
Interpreting the data
While 24-hour IOP monitoring gives insight into nighttime levels of IOP, the clinical relevance of the information remains unclear, noted Dr. Mansouri.
“We know IOP elevations during the daytime have an impact on glaucoma progression, but we do not know about the effect of rises in IOP at night. Data from a study in a rat model suggest the impact of elevated IOP at night may be worse, but we don’t know if the findings are applicable to humans,” he said.
In addition, whether mean IOP, peak IOP, short- or long-term fluctuation, or some other IOP parameter is the most important target for glaucoma management is also unknown.
“I also wonder whether there are specific IOP patterns, possibly independent of absolute levels, that are related to glaucoma development and may predict its future progression,” said Dr. Mansouri.
“With the ability to measure 24-hour IOP, we may be better equipped to answer these questions.”
Kaweh Mansouri, MD
This article is based on a presentation given by Dr. Mansouri at the 2015 Glaucoma Subspecialty Day. Dr. Mansouri is a consultant to Sensimed.