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Editorial Glaucoma Tonometry and Intraocular Pressure – Where are we Now? Julian García-Feijoo Professor and Chairman of Ophthalmology, Department of Ophthalmology, Hospital Clínico San Carlos; Universidad Complutense de Madrid, Instituto de Investigación Sanitaria del Hospital Clínico San Carlos (IdISSC), Madrid, Spain; Cooperative Research Network on Age-Related Ocular Pathology, Visual and Life Quality, Instituto de Salud Carlos III, Madrid, Spain Abstract Goldmann applanation tonometry has been the gold standard for measuring intraocular pressure for many years. However, it has some limitations, including the effects of several ocular variables such as axial length, curvature, rigidity and corneal thickness on the measurements. These limitations have prompted the development of new tonometers. Keywords Glaucoma, intraocular pressure, tonometry, rebound tonometer, dynamic contour tonometer, ocular response analyzer Disclosure: Julian García-Feijoo has received Clinical Trials/Research Support to his institution from SENSIMED and Tiolat. No funding was received in the publication of this article. This article is a short opinion piece and has not been submitted to external peer reviewers but was reviewed by the advisory board before publication. Open Access: This article is published under the Creative Commons Attribution Noncommercial License, which permits any noncommercial use, distribution, adaptation, and reproduction provided the original author(s) and source are given appropriate credit. Received: 14 July 2016 Pulished Online: 4 August 2016 Citation: European Ophthalmic Review, 2016;10(1):22–4 Correspondence: Julian García-Feijoo, Paseo de San Francisco de Sales 23, Casa 2,10B, 28003 Madrid, Spain. E: Glaucoma is an optic neuropathy, and although considered a multifactorial disease, it is the level of intraocular pressure (IOP) that is the main known risk factor for development and progression. There are other risk factors that can modify the effect of IOP on the development of glaucoma, but currently the main objective of glaucoma management is to preserve visual function by achieving a stable and continuous IOP decrease. Therefore, even if there are other factors to consider in glaucoma besides IOP, its assessment plays a fundamental role in the evaluation of the risk of conversion and progression. Goldmann applanation tonometry (GAT) is the gold standard for measuring IOP and most probably will continue to be so into the future. However, its limitations were obvious from the start and include the substantial effects of several eye variables such as axial length, curvature, rigidity and corneal thickness. Also, in some eyes, especially those with corneal problems (such as diseases, trauma, haze, corneal opacities, leucomas, etc.) and surgery, taking measurements is not easy. These limitations have prompted the development of new tonometers to improve the measurement of IOP. However, other pending questions exist, such as, which aspects of the IOP should be considered, and how do they interact with other factors? It has been clearly established that single snapshot IOP measurements do not provide enough information on the dynamic behaviour of the IOP. In fact, glaucoma is a 24-hour disease and the IOP exerts its effect on the ocular structures (including the optic nerve head, trabecular meshwork, etc.) all day long, on a daily basis. So, not only do we need to consider IOP variables such as fluctuation, peak pressure, IOP range, but also how these variables may impact eyes with different biomechanical and structural properties and also its complex interaction with other pressures (intracranial, translaminar, blood pressure, etc.). 22 Therefore, we need to start looking at IOP in a different way. IOP is a dynamic variable that fluctuates throughout a 24-hour period, yet patient follow-up is generally based on isolated IOP readings. It is true that we can adequately assess and manage the majority of glaucoma patients with single IOP measurements using GAT. However, one could question, is this really good enough, or could we do any better? The main challenges include: obtaining IOP measurements not influenced by the corneal properties; to develop technologies to measure the circadian IOP in clinical practice; and to understand better the complex interactions between IOP, other pressures and ocular biomechanics so we can effectively use the most relevant parameters to characterise the disease and improve patient care. Rebound tonometry (Icare ® and Icare ® PRO; iCare, Oy, Helsinki, Finland), is based on the induction rebound principle, but measurements obtained with it are affected by corneal thickness. 1,2 However, a clear advantage of the Iare PRO over the other four iCare models is that measurements may be taken with the patient lying or sitting/ standing. Also the small probe size of these tonometers facilitates its use in children and in eyes with corneal abnormalities and make it easier to measure IOP after corneal grafts, corneal rings, etc., as we can select the best area to measure. Therefore, although it is not a breakthrough, it addresses some practical problems of applanation tonometry. However, we also have to consider the increased cost of having to use disposable probes. Dynamic contour tonometer (DCT), or Pascal tonometer (SMT Swiss Microtechnology AG, Port, Switzerland) has a 7 mm diameter concave- surface probe that adapts to the cornea’s contour and does not alter its shape or curvature. An electronic pressure sensor embedded in the tonometer’s concave probe surface enables the direct measurement of transcorneal pressure. Such measurements are, at least a priori, TOU C H ME D ICA L ME D IA