IOP is a known risk factor for glaucoma, and yet there are no treatments that reliably lower IOP in all patients over their full lifetimes with minimal side effects. While effective pharmacological and surgical treatments to lower IOP are available, other approaches are needed. Berdahl and colleagues have developed a Multi-Pressure Dial system (MPD; Equinox Ophthalmic, Inc, USA) based on an airtight goggle system that allows the user to apply a negative barometric pressure (vacuum) to the tissues in the orbit, including the eye, to purportedly lower IOP. In this study, Tanner, Berdahl and colleagues test the safety and tolerability of the MPD system in 20 eyes of ten subjects with clinically documented open-angle glaucoma. The MPD goggles in this study were also fitted with a special port sealed with a thin latex membrane (like a Tonopen cover) that allows access to the cornea through the membrane for tonometry. Goggles were assessed for safety and tolerability for night wear in all patients and the MPD was set to -10 mmHg in the right eye for seven consecutive nights; the fellow eye was set to ambient atmospheric pressure (no vacuum).
The IOP reported reduction needs to be confirmed using a method that is not affected by the measurement technique itself
There were no significant adverse events and the googles were well-tolerated by the patients. IOP, BCVA, and retinal nerve fiber layer thickness were not affected by seven days of goggle wear, and the worst reported side effects were periorbital edema that resolved spontaneously after removal. Prior to the start of the study period, -10 mmHg MPD application significantly reduced IOP measured through the latex membrane by ~4 mmHg (p < 0.01), and approximately 3.5 mmHg at the end of seven consecutive nights of MPD goggle wear. While they have published on this tonometry technique in prior studies, it is likely to suffer somewhat from the 'Observer Effect', well-known in physics, wherein the act of making the measurement affects the outcome of the measurement itself. In this case, the traction force that a latex membrane (under slight tension from the vacuum in the goggles) applies to the underlying cornea may affect the IOP measurement itself. Overall, this safety study shows that the MPD is generally safe and well tolerated, but the IOP reported reduction needs to be confirmed using a method that is not affected by the measurement technique itself. If confirmed, the MPD could add another noninvasive tool to the clinicians' toolkit for lowering IOP at night.