Major ReviewSelf-tonometry in Glaucoma Management—Past, Present and Future
Introduction
Glaucoma is the leading cause of irreversible blindness in the world and the second leading cause of blindness in the world after cataracts.98 Numerous parameters have been studied over the last century to further the understanding and management of this disease, including the direct and indirect measurements of intraocular pressure (IOP), various forms of visual field testing, optic nerve and retinal nerve fiber layer estimation, central corneal thickness, the evaluation of the anterior chamber angle, and associated signs such as splinter hemorrhages. Intraocular pressure is the only modifiable factor and justifiably the primary target of glaucoma management.
The current approach is to measure the IOP at a routine office visit. We know, however, that the IOP varies over the course of a day and from day to day. It is also influenced by the cardiac cycle and blood pressure,87 ocular manipulation, including ocular massage and tonometry, the use of topical pressure-lowering medications and local anesthetics, previous ocular surgery, posture, stress (which may be quantified by allostatic load) and other unquantifiable factors such as measurement technique. Many other factors may affect the IOP, including exercise, diet, sleep patterns, viral illness, sinus congestion, and playing a musical instrument. With self-tonometry the patient can take regular measurements through the day and overnight, if required, in a familiar environment without stress. It is possible then to chart the diurnal pattern of the patient's IOP, discover any fluctuations, as well as monitor the effect of medications and patient compliance.
This information can be used to direct therapy and investigate glaucoma suspects. Indeed, Hughes et al in 2003 reported that 24-hour IOP monitoring changed the clinical management of 79.3% of the 29 patients in their study.60 The enthusiastic and reliable patient could also be taught to self-medicate according to their measured IOP. This may increase patient compliance by giving power and control back to the patient, similar to self-monitoring of blood glucose levels for the diabetes or spirometry for asthma. It may reduce the number of routine visits, but also expedite emergency evaluation of an acute angle closure attack. Remote centers where ophthalmic expertise is limited could also benefit from the telemedicine application of self-tonometry. Self-tonometry may also further our understanding of glaucoma pathophysiology in ocular hypertension and normal-tension glaucoma.
Section snippets
History
The measurement of IOP has evolved over the last century from invasive manometry to various tonometric approaches. Albrecht von Graefe invented the first impression tonometer in 1862,37 and this was followed by the Schiotz tonometer in 1906. The Goldmann applanation tonometer (GAT) was introduced in 1957 and has become the gold standard.51
Current Technology
As electronics and manufacturing technology progressed rapidly, new ideas and technical modifications spurred the development of a variety of self-tonometers.
Intraocular lens tonometer
The intraocular lens tonometer was first suggested by Collins in 1967.18 In this landmark paper Collins introduced the idea of a wireless passive intraocular sensor embedded into an artificial intraocular lens. The sensor consists of a capacitor whose two plates are pushed together when IOP is exerted on them. This alters the capacitance of the sensor and therefore its resonance frequency. The resonance frequency is then captured using the grid-dip technique with an external oscillator sweeping
The future of self-tonometry?
We can foresee the self-tonometer becoming an important part of the delivery of care to glaucoma patients. Potentially, it will be able to send readings to a secure central database that automatically flags fluctuating IOPs and alerts the treating ophthalmologist electronically. This will provide great benefit to patients who live remote to their treating ophthalmologist and may be useful for population screening programs.72, 83, 120
Ideal device?
The ideal device needs to be safe, reproducible, reliable and
Method of Literature Search
The literature review for this article was performed using Medline and the IEEE database using the search terms self-tonometry, Proview, pressure phosphene, Ocuton S, ICare, and combinations of self, intraocular pressure, glaucoma, tonometer and monitor. All years were covered. Additional sources include articles cited in the reference lists of other articles and Google search of the above terms. All articles were judged to be of clinical significance. All non-English articles were considered
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EYEMATE-SC Trial: Twelve-Month Safety, Performance, and Accuracy of a Suprachoroidal Sensor for Telemetric Measurement of Intraocular Pressure
2023, OphthalmologyCitation Excerpt :Briefly, it consists of a cushion-shaped sensor device for permanent implantation into the suprachoroidal space and an external handheld reader device (Mesograph). The EYEMATE-SC sensor bears the same microelectromechanical system as the EYEMATE-IO implant,7,8,11,13 although the implant is miniaturized in its final dimensions (7.5 × 3.5 mm and an outwardly decreasing thickness of 1.3 mm at the center and 0.9 mm in the periphery). The surface shape of the implant is rounded lenticularly to adapt to the curved scleral shape smoothly (Fig 1).
Safety and performance of a suprachoroidal sensor for telemetric measurement of intraocular pressure in the EYEMATE-SC trial
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2020, BMJ Open OphthalmologyPotential therapeutic usage of nanomedicine for glaucoma treatment
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2019, Microsystems and Nanoengineering
The authors reported no proprietary or commercial interest in any product mentioned or concept discussed in this article. The authors would like to thank Professor Nigel Lovell, School of Biomedical Engineering, University of New South Wales, Prof. Dr. Dieter Baumgarten, and Marcel van Brakel for their expert advice in the authorship of this review.