Development of contact lens based 24-hour intraocular pressure (IOP) monitoring device (Triggerfish: Sensimed AG) may provide a new tool to evaluate glaucoma risk factors. This contact lens sensor does not measure IOP itself, but the sensor collects electronic output signals associated with tissue volumetric changes in the corneoscleral region. Therefore, data are related to IOP change as well as tissue biomechanical properties reflecting how they are altered by the IOP change. The present multicenter, retrospective cohort study using a relatively large sample of 445 treated open-angle glaucoma patients aimed to isolate principal components of 24-hour IOP-related pattern correlated with the rate of visual field progression within a time frame of about five years. Results indicated, in addition to the mean peak ratio (related to the output signal height and time to reach the height) during the wake period, a few components during the sleep period (number of long peaks, variation of bursts ocular pulse frequency, and variation of bursts ocular pulse amplitude) were also correlated.
Most critically, the newly identified sensor signal variables from a single 24-hour time period showed overall a better statistical correlation with the rate of glaucoma progression than the current clinical standard, the mean of multiple office-hour Goldmann IOP readings taken over years. It should be noted that both the newly discovered principal components from the contact lens sensor output signals and the traditional Goldmann IOP readings can only explain 20-30% of the visual field progression in statistical terms as articulated by the authors. Confirmed in the present study, an important advantage of using the contact lens sensor to study glaucoma progression is the short period time of 24 hours. Clinical research involving a single or multiple 24-hour time period are likely easier to manage than a clinical research involving several years' data collection. For this reason, major confounding factors discussed by the authors in the article can be evaluated by repeated contact lens sensor recordings; for example the confounding factors related to IOP-lowering treatments during the follow-up years. Applying similar statistical analyses in a study that collects contact lens sensor output signals from a group of patients prior to and after IOP-lowering glaucoma medications may identify those components related to tissue biomechanical properties independent from the reduction of IOP. Components associated with a specific IOP-lowering medication in the 24-hour signal outputs from the sensor may also be evaluated. These potential studies are straightforward, and the requirement of study time is relatively short compared to the collection of Goldmann IOP readings over years. It is reasonable to expect from these studies additional independent components in the 24-hour signal pattern generated by the contact lens sensor that are associated with glaucoma progression. These independent components or a combination of these independent components plus the traditional Goldmann IOP readings may show us more insights for the unexplained 70-80% of disease progression in open-angle glaucoma patients.