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Editors Selection IGR 12-2
Clinical Examination Methods: Telemetric tonomtery
Comment by John Liu on:
60318 Implantation of a novel telemetric intraocular pressure sensor in patients with glaucoma (ARGOS study): 1-year results, Koutsonas A; Walter P; Roessler G et al., Investigative Ophthalmology and Visual Science, 2015; 56: 1063-1069
Recent advances in wireless technology have provided opportunities for developing sophisticated medical devices for monitoring intraocular pressure (IOP), the most significant risk factor for glaucoma. Koutsonas et al. reported their early experience in a clinical trial of an implantable wireless IOP sensor. The trial enrolled six patients (aged 70-76 years) with cataract and primary open-angle glaucoma. Toward the end of cataract surgery, a ring-shaped telemetric IOP sensor was implanted in the ciliary sulcus. The authors reported the tolerability of this sensor in detail as well as IOP data selected throughout the first postsurgical year. As anticipated, temporary adverse events occurred due to the implanted sensor.
Comparison of IOP readings obtained between the external IOP reader and the standard Goldmann tonometer showed that the correlation of these two sets of IOP readings was short of what we hoped for
However, there was no adverse impact on vision at the one-year checkup except some narrowing of the anterior chamber angle. Measurements of IOP were performed during office visits and also by the patients at home using an external IOP reader. Comparison of IOP readings obtained between the external IOP reader and the standard Goldmann tonometer during the office checkups was shown. By visual inspection of IOP data, the correlation of these two sets of IOP readings was short of what we hoped for. A side-by-side evaluation indicated that the IOP difference was larger than the clinically acceptable IOP accuracy when using the Goldmann tonometer (two to three mmHg). Also, there was a critical lack of consistency in the IOP difference between the two measuring devices.
The report brings us good news that this implantable IOP sensor seems to be well-tolerated up to one year. The associated medical risk is not high. While a longer follow-up is certainly warranted for these six patients, recruitment of more subjects for similar clinical trial will not be inappropriate. Unfortunately, this device does not have the accuracy as hoped. One may argue that inaccuracy can be overcome if IOP consistency exists and in vivo calibration can be done. Unlike a contact lens based IOP sensor, a permanent implanted IOP sensor should have a high consistency of determining IOP in practice. What causes the inconsistency of this IOP sensor is uncertain and should be investigated. Patients who have the implanted IOP sensor can easily collect data at home for a study of IOP consistency, for example the well-defined postural IOP difference and the diurnal IOP curve. It is possible the authors are already proceeding with this research project. There will be plenty of IOP data to study, which is part of the goal for developing this IOP monitoring device in the first place.
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