Current glaucoma management involves periodic measurement of IOP every few months which is recognized to be suboptimal. Consequently, the development of implantable IOP sensors that enable continuous measurement has been a long-standing goal.1 Szurman et al. report on the results of a clinical trial to assess the safety, performance and accuracy a novel suprachoroidal telemetric IOP sensor (EYEMATE-SC, Implandata Ophthalmic Products GmbH, Hannover, Germany).2 The basic design is similar to past devices from Implandata with a silicone rubber encapsulated custom application-specific integrated circuit (ASIC) chip that integrates pressure and temperature sensors, identification and analog-to-digital encoders, and a telemetry unit. IOP readings are obtained by using an external hand-held reader which powers the implant wirelessly and collects the pressure readings based on an average of 10 samples. The main difference with this new device is the smaller form factor (7.5 x 3.5 x 1.3 mm) designed to be placed in the suprachoroidal space instead of the ciliary sulcus.
In this trial, 24 eyes of 24 primary open-angle glaucoma patients scheduled to undergo non-penetrating glaucoma surgery (NPGS ‐ canaloplasty or deep sclerectomy) were enrolled. The suprachoroidal space was accessed underneath the scleral flap and expanded with viscoelastic. Comparisons between EYEMATE-SC IOP readings and Goldmann applanation tonometry (GAT) using a two-person technique were performed at one, three, ten, 30, 90, 180, 270, and 360 days post-operatively. Overall agreement between GAT and EYEMATE-SC was good based on Bland-Altman analysis (mean difference 0.8 mmHg; 95% limits of agreement [LoA], -5.1 to 6.7 mmHg). Interestingly, the agreement appeared to be higher in the early post-operative period with a maximum difference of 2.5 mmHg (95% LoA, -5.1 to 10.1 mmHg) at day ten, but improving to a mean difference of -0.3 mmHg (95% LoA, -4.2 to 3.6 mmHg) at day 360. The authors speculate that this may be due to early transient astigmatism that resolved after the first 30 days. Excluding the first 30 days, the mean difference was -0.2 mmHg (95% LoA, -4.6 to 4.2 mmHg). No cases of device migration, rotation, or dislocation were reported. No serious complications were reported, and the most common post-operative complication (hyphema) was attributable to the glaucoma surgeries.
This study demonstrates a number of advancements compared with previous devices placed in the sulcus. Most obvious is the different form factor and location, which enables use of the device in phakic patients, and is well-suited in combination with NPGS. However, the most important difference appears to be the improved accuracy and stability of the device compared with previous reports of the EYEMATE-IO.3,4 It is not clear if this is due to the suprachoroidal placement or improvements in the technology, but agreement with GAT appears to be very good at one year post-operatively. An important limitation is that the device does not provide continuous IOP monitoring, but instead allows intermittent measurement with a hand-held reader ad libitum. While this is certainly an improvement over current clinical practice, it does not currently capture the nocturnal period. Also, longer term follow-up will be required to ensure safety and performance of the device for an implant that is expected to function for many years. Nevertheless, this study represents an important milestone with a reliable, well-tolerated, implantable pressure sensor in the suprachoroidal space.