24-hour monitoring to revolutionize glaucoma care

By Cheryl Guttman Krader

The availability of technology for 24-hour IOP monitoring will be a transformative event in the management of glaucoma, said Robert N. Weinreb, MD, in his delivery of the first annual Drs. Henry and Frederick Sutro Memorial Lecture.

He predicted that within the next five years, the plethora of data generated from 24-hour IOP monitoring would provide deeper insight about glaucoma onset and progression and lead to a paradigm change in patient care.

“We know that a single measurement of IOP during usual office hours provides insufficient information for guiding management decisions in patients with glaucoma,” said Dr. Weinreb, chairman of ophthalmology, director of the Shiley Eye Center and Hamilton Glaucoma Center, University of California, San Diego. “Although clinicians might maximize the value of in-office IOP evaluation by obtaining multiple measurements throughout the day, such measurements rarely include nocturnal IOP measurements.

Dr. Weinreb added that 24-hour IOP monitoring holds the key to personalizing IOP control for optimal glaucoma management, and it will allow physicians to fully elucidate the importance of different IOP parameters on glaucoma progression.

The insufficiency of using a snapshot measurement of IOP to guide clinical decision-making in glaucoma is underscored by data highlighting the variability of IOP, both in terms of short-term and long-term fluctuations, along with the lack of knowledge about what IOP parameter (e.g., peak, 24-hour mean, or fluctuation during the day or a longer time period) has the greatest prognostic significance.

IOP-variation studies

Dr. Weinreb and colleagues have been leading contributors to current understanding of IOP variations through the work they began 20 years ago when they established a sleep laboratory at the University of California, San Diego. In studies that have included more than 1,500 patients, they developed insights on IOP circadian rhythm, effects of postural change, and the 24-hour IOP-lowering effects of the various classes of ocular hypotensive medications.

In the latter investigations, they found that beta-blockers and alpha-agonists were very effective in reducing IOP during the day, but had no IOP-lowering benefit at night. In contrast, prostaglandin analogues and carbonic anhydrase inhibitors were found to have good 24-hour, IOP-lowering activity, as did laser trabeculoplasty.

The findings are consistent with the mechanisms of action of the different classes of medication and the circadian rhythms of aqueous humor production and uveoscleral outflow. However, considering research indicating the importance of perfusion pressure and translaminar pressure (the difference between intracranial pressure and IOP) as risk factors for glaucoma and its progression, Dr. Weinreb said there may be issues to consider in addition to IOP for selecting optimal medical therapy.

He noted that blood pressure and perfusion pressure at night are lowered by the beta-blockers, but not by the prostaglandin analogues or carbonic anhydrase inhibitors. In animal studies, some alpha-agonists have neuroprotective effects.

“We will come to learn that drugs with 24-hour, IOP-lowering efficacy and that do not lower perfusion pressure will be preferred medications,” he said. “However, additional effects, such as neuroprotection or the ability to enhance blood flow to the optic nerve, will be important. In fact, there is some clinical data that hints that the alpha-agonist brimonidine has neuroprotective effects and was more effective than timolol for preserving the visual field (LOGTS Study).”

IOP-monitoring technology

The approaches for 24-hour IOP measurement are based on use of either temporary or permanently placed devices. A temporary modality (Triggerfish, Sensimed) is a contact lens-based system that detects changes in corneal curvature rather than IOP. The device has received the CE mark, but it is not yet approved in the United States. Implantable devices for monitoring IOP that provide the data via telemetry are being developed by Implandata, AcuMEMS, as well as others are still in clinical trials.

Although the contact lens-based sensor has the advantage of being noninvasive, Dr. Weinreb believes the permanent-monitoring approaches will be a better solution for obtaining accurate IOP measurements over long durations.

“Once that information is available, one will be able to refine our concept of target IOP and know if it is the peak, mean, fluctuation, or some other parameter that matters,” he said.

“More importantly, drug-delivery devices and surgical techniques will be integrated with these IOP-monitoring devices in ways that will optimize control of IOP.”