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Editors Selection IGR 15-2
Clinical Examination Methods: IOP fluctuation
Comment by Tony Realini on:
57023 Circadian intraocular pressure patterns in healthy subjects, primary open angle and normal tension glaucoma patients with a contact lens sensor, Agnifili L; Mastropasqua R; Frezzotti P et al., Acta Ophthalmologica, 2015; 93: e14-e21
Agnifili and colleagues from Italy have conducted an interesting prospective study in which healthy subjects, normal-tension glaucoma patients, and primary open-angle (high-tension) glaucoma patients (one eye from ten individuals in each group) underwent continuous 24-hour intraocular pressure (IOP) monitoring using the Triggerfish contact lens-based device. The Triggerfish device does not directly measure IOP but rather infers it based on changes in corneal curvature; the device's output is not measured in pressure units but in millivolt equivalents. The outcome of interest was the 24-hour IOP pattern of each group. Such studies have been completed previously, albeit using intermittent (every one to three hours) IOP assessments via more familiar tonometers (Goldmann, pneumotonometer, etc.); a few 24-hour studies have also been conducted with the Triggerfish, but these have not directly compared outcomes in different patient groups. This study's results support that the device's output does reflect IOP qualitatively: as is known from prior studies, the current study demonstrated nocturnal IOP peaks in all three groups. Interestingly, both the height and the breadth of the nocturnal peak was greatest in the POAG group, followed by the NTG group, and finally by the normal group.
It is important to identify the specific IOP behaviors that increase the risk of progression
Taken on their own, these data reveal potential differences in circadian IOP variability both between the glaucomatous and normal states, and smaller (and insignificant given the sample size) differences between POAG and NTG. In a broader context, this study ‒ like others before it ‒ offer a preview of the potential clinical application of this and other continuous IOP monitoring devices. Certainly there will not be a need to know the circadian behavior of every one of our glaucoma patients ‒ for instance, it would have little relevance in a patient with stable structural and functional parameters. In a progressing patient ‒ particularly one whose daytime office-based IOP seems adequately controlled ‒ characterization of nocturnal IOP could reveal uncontrolled IOP elevations that might warrant more intensive nighttime therapy to suppress. Much more work is necessary, however, to more fully characterize circadian IOP using this and other devices. For, as this study demonstrates, even normal subjects exhibit nocturnal IOP elevations. Given this, what is the clinical relevance of a nocturnal IOP rise in a progressing glaucoma patient? Continuous circadian IOP monitoring addresses the problem we face of a low sampling rate for IOP assessment. What remains, however, is to identify the specific IOP behaviors that increase the risk of progression.
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