Choritz and colleagues have reported the 12-month outcomes of the ARGOS study, evaluating the safety and preliminary performance of an implantable continuous IOP monitor into the ciliary sulcus at the time of cataract extraction and IOL implantation. The system is in two parts: an implantable microelectro-mechanical sensor that detects and converts IOP to electrical signals, and an external detector that, when held in close proximity to the eye, activates and downloads IOP data. In this study, 22 eyes with POAG received the device. Surgical complications associated with the device included 5 cases each of iris prolapse (likely related to the requirement to enlarge the phacoemulsification incision to 6mm to accommodate device insertion) and pigment dispersion (also likely related to insertion). Four serious postoperative adverse events were reported, including two cases of severe fibrin reaction in the anterior chamber (both of which resolved with anti-inflammatory therapy), one case of corneal decompensation, and one case of intractable IOP elevation requiring filtering surgery. Mean endothelial cell loss was 9.4% at 12 months (largely related to the single case of corneal decompensation). Performance-wise, mean IOP measured with the device averaged 3.2 mmHg higher than Goldmann tonometry, while the agreement was high (intraclass correlation coefficient 0.783). Importantly, the device can be recalibrated post-implantation, minimizing consequences of long-term drift. This device and study represent an important step toward the holy grail of accurate and continuous IOP monitoring in eyes with glaucoma.
This device and study represent an important step toward the holy grail of accurate and continuous IOP monitoring in eyes with glaucoma
While the relationship between IOP and glaucoma has been known for more than a century, we still know remarkably little about the nature of the relationship. That is to say, we do not fully understand which aspects of IOP behavior (mean, peak, variability, extent of time above a certain level, etc.) that increases the risk of progression over time. This gap in our knowledge is attributable in large part to a very low sampling rate-absent reliable and safe self-tonometry or continuous tonometry, we simply cannot collect enough IOP data at three to four office visits per year to characterize IOP behavior robustly enough to elucidate the IOP-progression relationship. This device - or one like it - may help to narrow or close that gap. In the short term, such a device would likely provide an adequate quantity of IOP data to better assess the adequacy of IOP control in a given eye and to assess the efficacy of newly initiated treatments. In the long term, with a better understanding of the IOP-progression relationship, we may be able to risk-stratify patients at diagnosis based on IOP behavior, which may guide our therapeutic choices.