August 16, 2012 — A study testing the safety and tolerability of a contact lens sensor designed to assist in the diagnosis and management of glaucoma suggests that the device is safe and relatively well tolerated.
The sensor, discussed in a study published online August 13 in the Archives of Ophthalmology, was designed to measure intraocular pressure during a 24-hour period.
"The results are of importance since the availability of a practical device for ambulatory monitoring of 24-[hour intraocular pressure] is an unmet need in glaucoma," the study's lead author, Kaweh Mansouri, MD, MPH, from the Hamilton Glaucoma Center and Shiley Eye Center, Department of Ophthalmology, University of California, San Diego, in La Jolla, said in an email to Medscape Medical News.
The trial was conducted in hopes that the US Food and Drug Administration will ultimately approve the contact lens sensor, Dr. Mansouri said.
The aim of the study was to test the safety, reproducibility, and tolerability of day-long monitoring with the contact lens sensor.
Forty people who either had glaucoma (n = 19) or were suspected of having glaucoma (n = 21) made up the subject pool. The patients took part in two 24-hour intraocular monitoring sessions 1 week apart.
The researchers monitored for adverse events, assessed the tolerability of the contact lens via visual analogue scales, and determined the reproducibility of the signal patterns between the intraocular monitoring sessions, using Pearson correlations.
The mean age of the participants was 55.5 ± 15.7 years, and 60% were male. "The mean (SD) visual analog scale score was 27.2 (18.5) mm in [the first session] and 23.8 (18.7) mm in [the second session] (P = .22)," write the authors. The results indicated that the correlation between the 2 sessions for all patients was 0.59, and when stratified for use of antihypertensive glaucoma eyedrops vs no glaucoma medication, the Pearson correlations were 0.63 vs 0.51, respectively (P = .12 for the difference). The most prominent adverse events were blurred vision (82%), conjunctival hyperemia (80%), and superficial punctate keratitis (15%).
To study the change in signal of the contact lens sensor from "the wake/sitting to the sleep/supine state, linear regressions were fitted to the transition from the wake to the sleep period," the authors explain. From wake to 2 hours into sleep, mean positive linear slopes of the sensor signal were detected in both sessions for the group that received no glaucoma medication (first session: 0.40 [P < .001]; second session: 0.33 [P < .01]), but not for the group that received glaucoma medication (first session: 0.24 [P = .06]; second session: 0.40 [P <.001]).
"To our knowledge, the current study is the first to assess the short-term reproducibility of [intraocular pressure] patterns throughout the full 24-hour cycle," the authors write, "including undisturbed sleep made possible through the availability of the [contact lens sensor] for clinical use."
Limitations include that the current technology does not display output signals in millimeters of mercury but, rather, in "arbitrary units...proportional to the electric signal generated by the contact lens–embedded strain gauge." This is why the authors used Pearson correlations, an indirect representation of reproducibility, instead of intraclass correlation coefficients. In addition, potential confounders such as sleep times, physical activity, and environmental factors were not controlled; also, it is unclear whether the contact lens sensor will be safe and well-tolerated in an older population.
Nonetheless, "[t]his study reveals that [the contact lens sensor] provides a safe and well-tolerated approach to 24-hour [intraocular pressure] monitoring in glaucoma patients," the authors conclude. "The 24-hour [intraocular pressure] patterns seem to be fairly reproducible when repeated in the short term. The availability of continuous 24-hour [intraocular pressure] monitoring holds the promise to improve glaucoma care." Outside experts agree with the researchers.
First Steps Toward Continuous Intraocular Pressure Measurement
"[I]t's first steps towards what I would describe as the Holy Grail of being able to measure intraocular pressure more or less continually in a tolerable way," noted James Brandt, MD, a professor of ophthalmology and director of the Glaucoma Service at the University of California, Davis.
It is important to be able to measure intraocular pressure continuously for a few hours, a few days, "or ideally for weeks at a time to get a better understanding of how the patient's pressure is managing," he explained in an interview with Medscape Medical News.
At this time, the standard way to measure intraocular pressure is to check it "only for a few milliseconds a year," Dr. Brandt said. The problem, however, is that intraocular pressure is dynamic and changes at different points throughout the day, he explained. In fact, the authors cite research from controlled sleep laboratories showing that intraocular pressures are highest "during the nocturnal/sleep period with the patient in the supine position."
This new sensor is not terribly relevant to primary care physicians, Dr. Brandt said, "other than the fact that they may not realize that intraocular pressure is not a static thing."
He points to an analogy using diabetes management: "Nobody would manage diabetes based on a single blood sugar taken randomly once in a while, with no thought of the underlying physiology...and yet that's what we're doing [for] glaucoma."
For the general ophthalmologists, the message is more to "stay tuned," Dr. Brandt said. The technology will probably come about at a practical level in the next 5 to 10 years, he predicted, but added that, "[i]t remains to be seen whether or not" it will be useful for all types of patients, including those who have never before worn contact lenses.
The device will help ophthalmologists assess changes in 24-hour intraocular pressure both before and after interventions for pressure control in glaucoma, Dr. Mansouri said in an email.
"The availability of this technology is a milestone in glaucoma," he said, "and has the potential to significantly improve the management of glaucoma by providing better ways to assess treatment efficacy and possibly risk assessment for progression."
Laboratories across the country are working on similar technologies such as an implantable device that can measure intraocular pressure in the eye around the clock or some other type of disposable and inexpensive lens that functions similarly to the one described in this article, Dr. Brandt noted.
There will be challenges, however. Because of the generation of an "enormous" amount of data from the 24-hour and longer monitoring periods, "we're going to have to develop software algorithms and other approaches to management of massive data sets to pull out what the important signal is," Dr. Brandt warned.
This study was supported by Sensimed AG, by an unrestricted grant from Research to Prevent Blindness, and by the Velux Foundation. Sensimed AG participated in the design of the study. Dr. Mansouri is a consultant for Sensimed AG, the manufacturer of the device. One coauthor has reported working as a consultant and receiving research and material support from Alcon Laboratories Inc, working as a consultant and receiving research support from Allergan Inc, receiving research and material support from Carl Zeiss Meditec Inc, working as a consultant and receiving research and material support from Pfizer Inc, and receiving research support from Reichert Inc and Sensimed AG. One coauthor has reported working as a consultant and receiving material support from Carl Zeiss Meditec, receiving material support from Heidelberg Engineering GmbH and Nidek, working as a consultant and receiving research material support from Optovue, receiving material support from Topcon Medical Systems, and working as a consultant for Sensimed AG. Dr. Brandt has disclosed no relevant financial relationships.
Arch Ophthalmol. Published online August 13, 2012. Abstract
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