Devising a way for IOP to be frequently measured outside of a clinic or lab without the help of a medical professional has long been an objective in the field of glaucoma. And, with a few new options, this concept is now a reality. One device for personal monitoring of IOP is already in clinical use, and a second is FDA-approved but undergoing further evaluation. A third device is approved in Europe and headed for a U.S. pilot study. Personal, a.k.a. “self” or “home,” IOP monitoring promises to provide answers to many questions about glaucoma, and is already making a difference in patient care.

Questions in Need of Answers

Inder Paul Singh, MD, The Eye Centers of Racine and Kenosha in Wisconsin, explains why personal IOP monitoring is important.

“Right now, patients typically have their IOP measured only one time out of a 24-hour day, one day out of a few months, a few months out of a year,” he says. “We’re missing a true understanding of the actual dynamics of the pressure of the eye and the aqueous out-flow system.”

When a device can record IOP automatically or enable patients to check their own, measurements can be taken frequently throughout the day or night, providing a far more accurate picture of what’s going on. Fluctuations in IOP, which are known to occur within a 24-hour period and in different patterns over time, are thought to be associated with progression of the disease and are of the most interest.

Knowing a patient’s true IOP levels, especially if and when pressure spikes occur, can reveal the need for tighter IOP control through different or more aggressive treatment. In the longer-term, once large amounts of IOP data can be studied, answers to other questions may emerge. For example, Dr. Singh says,

“This should help explain why some patients’ glaucoma gets worse despite what seem to be ‘controlled’ pressures in the office. We may learn whether everyday activities such as wearing a necktie or doing yoga might raise episcleral venous pressure, which is a factor in the regulation of IOP, and whether some patients are more susceptible to that.”

Furthermore, as Sanjay G. Asrani, MD, of Duke University Eye Center, North Carolina, points out, “While there is consensus that fluctuation in IOP leads to glaucoma progression, we don’t know which aspect of the fluctuation is really causing the damage. Is it the peak, the delta, the difference between the trough and the peak, the number of times the peak occurs? Having multiple readings over time will help figure that out.”

In Practice and in the Pipeline

Glaucoma specialists will be hearing more about the following three devices for personal IOP monitoring.

Icare HOME tonometer (Icare USA)

Patients use the Icare HOME tonometer, cleared by the FDA in March, to take their own IOP measurements, which are stored in the device and retrieved by the doctor via Icare LINK software. No anesthesia is required. Rather than an air puff, the tonometer utilizes rebound technology, which has been shown to correlate with Goldmann applanation tonometry (GAT).^1,2

Dr. Asrani sends the device home with patients whose OCT or visual field tests suggest disease progression despite what appear to be on-target IOP measurements in the clinic. (He doesn’t use the device for patients with corneas thicker than 590 microns or those with corneal edema or transplants, all of which could interfere with accurate readings.) He asks patients to record their IOP a minimum of three times each day, five times if possible, for 3 weeks.

“We have found that indeed the pressures are not really controlled, and that’s why they’re progressing,” he says.

Using the Icare HOME recently convinced a previously reluctant patient, a working-age, monocular male, to undergo tube surgery. Over several years, his in-clinic IOP measurements had been 11 to 12 mmHg, but visual field testing was showing gradual possible progression. Multiple readings on multiple days with the home tonometer captured pressures reaching into the high teens and low 20s and as high as 23 mmHg in the late evening.

Triggerfish (Sensimed)

The Triggerfish system consists of a silicone contact lens embedded with a micro-sensor that captures spontaneous circumferential changes at the corneoscleral area. The information transmits wirelessly to an adhesive antenna that is placed around the eye and then through a thin cable to a portable recorder worn by the patient. At the end of a 24-hour recording period, the information is transferred via Bluetooth from the recorder to software on the physician’s computer.

Although not a direct measure of IOP, the ocular dimensional changes assessed by Triggerfish have been shown to be closely related to IOP curves and associated with the rate of visual field progression in treated glaucomatous eyes.³

The Triggerfish received FDA approval in 2016, but, rather than launching the product right away, Sensimed is executing a study to confirm its utility in predicting the course of glaucoma progression and to further establish ocular volume change patterns as a stand-alone biomarker for use in the management and treatment of glaucoma patients.

EYEMATE (Implandata Ophthalmic Products GmbH)

The EYEMATE is a ring-shaped, implantable, telemetrically powered IOP-sensing microchip that is read by the patient with a handheld mesograph. The measurements, which have shown similar profiles to those of GAT,⁴ are transferred wirelessly to a cloud database accessible by the doctor. A version of the EYEMATE that is implanted in the sulcus during cataract surgery received approval in Europe earlier this year. A U.S. pilot study is expected to begin in the second half of 2018. The study, which will involve approximately 12 patients and either that implant or a suprachoroidal version that could be implanted without cataract surgery,⁵ will evaluate safety and the sensor’s correlation with GAT.

According to Implandata’s Max Ostermeier, “The final decision is not made yet, but most probably we would enter the FDA process with the suprachoroidal sensor implant and wait with the intraocular design until we have integrated the sensor into an intraocular lens.”

A pivotal study for obtaining FDA approval would follow in 2019.

Another Piece of the Puzzle

Dr. Singh says doctors will be watching closely as technologies for personal monitoring of IOP mature, with particular interest in their accuracy and reliability. Education will be key, too, he says, because patients will need to understand that self-monitoring doesn’t replace doctor visits.

“That said,” he continues, “the information to be obtained from such devices will give us another important piece of the glaucoma puzzle, a better understanding of disease progression and how best to treat each patient.” Dr. Asrani agrees, adding that this group of technologies “will open a completely new era in glaucoma management.” GP

References

1. Termühlen J, Mihailovic N, Alnawaiseh M, Dietlein TS, Rosentreter A. Accuracy of measurements with the iCare HOME rebound tonometer. J Glaucoma. 2016;25(6):533-538.
2. Asrani S, Chatterjee A, Wallace DK, Santiago-Turla C, Stinnett S. Evaluation of the ICare rebound tonometer as a home intraocular pressure monitoring device. J Glaucoma. 2011;20(2):74-79.
3. De Moraes CG, Jasien JV, Simon-Zoula S, Liebmann JM, Ritch R. Visual field change and 24-hour IOP-related profile with a contact lens sensor in treated glaucoma patients. Ophthalmology. 2016;123(4):744-753.
4. Koutsonas A, Walter P, Roessler G, Plange N. Implantation of a novel telemetric intraocular pressure sensor in patients with glaucoma (ARGOS study): 1-year results. Invest Ophthalmol Vis Sci. 2015 Jan 22;56(2):1063-1069.
5. Mariacher S, Ebner M, Januschowski K, Hurst J, Schnichels S, Szurman P. Investigation of a novel implantable suprachoroidal pressure transducer for telemetric intraocular pressure monitoring. Exp Eye Res. 2016 Oct;151:54-60.