Muniesa and colleagues have conducted a prospective comparison of 24-hour fluctuations in intraocular pressure (IOP) in eyes with open-angle glaucoma (OAG) treated either with medical therapy (and no history of glaucoma surgery) or surgical therapy (one-third of whom were also receiving medical therapy). IOP fluctuations were measured with Sensimed Triggerfish contact lens sensor, which infers IOP changes based on changes in ocular shape at the limbus over time and reports its output in units referred to as millivolt equivalents (mv Eq). The group found significantly higher fluctuations (the outcome measure being amplitude of the mathematically-smoothed 24-hour mv Eq tracing) in the medically-treated group compared to the surgically-treated group (131 versus 100 mv Eq, respectively; p = 0.01). The implication is that surgery more effectively reduces IOP variability than medical therapy in eyes with OAG. There are, however, several important caveats to this conclusion. The true relationship between mv Eq and IOP is undefined. It may not be linear. Thus, the equivalent 24-hour IOP fluctuations may be greater or less than the mv Eq fluctuations, and the clinical significance of these findings cannot be known. More importantly, the very significance of IOP variability is incompletely characterized. The investigators reported that significantly fewer surgically-treated eyes than medically-treated eyes manifested nighttime peaks in mv Eq (14% versus 43%, p = 0.011). Unfortunately, the relevance of nighttime IOP peaks is unclear. Even healthy subjects have higher IOP at night. Until we better understand the specific characteristics of IOP variation over time that confer risk of the development and/or progression of glaucoma, studies such as these are challenging to discuss in the context of clinical implications.
Until we better understand the specific characteristics of IOP variation over time that confer risk of the development and/or progression of glaucoma, studies such as these are challenging to discuss in the context of clinical implications