Modalities of Tonometry and their Accuracy with Respect to Corneal Thickness and Irregularities

Abstract

Recent advances in tonometry have led to the development of a number of devices with differing clinical applications. Their role in cases of abnormal corneal thickness and surface irregularities is particularly important, as inaccurate estimation of the true intraocular pressure (IOP) in such cases may lead to suboptimal evaluation. The purpose of the present review was to evaluate the accuracy of the most widely used devices in cases of corneal thickness and surface irregularities, based on a survey of the published literature. The analysis was based on a Medline search focusing mainly on papers that have evaluated the devices' accuracy with respect to corneal thickness and irregularities. Nine device types (Goldmann tonometer, Tono-Pen, Perkins tonometer, Ocular Response Analyzer, non-contact tonometer, pneumatonometer, I-Care rebound tonometer, Pascal dynamic contour tonometer (DCT) and Phosphene tonometer) were described in detail. Moreover, the physical principles and major utility of each tonometer were compared. Each of the many different commercially available tonometers has specific advantages and disadvantages. New non-invasive technologies are getting closer to a precise estimation of the true IOP. However, among all tonometers, none is highly accurate when both corneal thickness and surface irregularities are present. Fifty years after its development, Goldmann tonometry remains the gold standard to which all other devices are compared. RESUMENAvances recientes en el campo de la tonometría han propiciado el desarrollo de diversos dispositivos con diferentes aplicaciones clíni-cas. Resulta de particular importancia el papel que juegan en el caso de espesores corneales anormales o en presencia de irregularidades en la superficie de la córnea, puesto que, en esos casos, una medida imprecisa de la presión intraocular (PIO) real puede traer como consecuencia una valoración incorrecta del caso. El objetivo de esta revisión es evaluar el grado de precisión de los dispositivos más utilizados hoy en día en casos en los que existen irregularidades en la superficie de la córnea o en el espesor corneal. Para ello, se llevó a cabo una búsqueda de datos entre los artículos publicados. El análisis estuvo basado en una búsqueda bibliográfica realizada dentro de Medline, centrándose principalmente en aquellos artícu-los científicos que habían estudiado el grado de precisión del dispositivo en función del espesor corneal del paciente y de la presencia o no de irregularidades corneales. Se describen en detalle nueve tipos de dispositivos: tonómetro de Goldmann, Tono-Pen, tonómetro de Perkins, Ocular Response Analyzer, tonómetro sin contacto, neumotonómetro, tonómetro de rebote I-Care, tonómetro de contorno dinámico Pascal y tonómetro de fosfeno. Además, se presentan de forma comparada los principios físicos en los que está basado cada tonómetro y las situaciones en las que cada uno resulta de mayor utilidad. Cada uno de los distintos tonómetros disponibles en el mercado presenta ventajas y desventajas respecto...

Glaucoma: the retina and beyond

“…The gold standard is Goldman applanation tonometry (GAT), but other devices exist and are used in optometric practice and in research settings, such as non-contact tonometry (e.g. Pulsair), rebound tonometry, and ocular pulse analyser [127]. An increasingly recognised limitation of IOP measurement by tonometry is that a thicker central cornea, as measured by ultrasound pachymetry, leads to a higher measured IOP than is present, whereas a thinner central cornea underestimates the true IOP [107].…”

Review of the measurement and management of 24-hour intraocular pressure in patients with glaucoma

“…Conversely, in a review of the different modalities of tonometry and their accuracy with respect to corneal thickness and irregularities, the Tono-Pen was reported to underestimate IOP compared to measurements obtained with GAT, as well as overestimate or underestimate IOP depending on variables such as baseline IOP and central corneal thickness. 95 Owing to the potential differences between techniques, it may be preferable to use a single tonometric technique over the entire 24-hour period, although this was a less common approach within the studies identified. One study conducted PAT in the habitual position throughout the 24-hour period 131 ; 3 studies used the Tono-Pen XL (BioRad, Glendale, CA) to measure 24-hour habitual IOP in addition to 24-hour supine IOP (i.e., supine and sitting measurements during the daytime; supine measurements only during the nighttime) 101e103 ; and 8 studies used noncontact tonometry to measure IOP in the habitual position.…”

Correlation of Tono-Pen and Pneumatonometer Measurements from Four Scleral Quadrants with Intraocular Pressure Measurements from the Cornea

“…Goldmann applanation tonometry (GAT) remains the gold standard for IOP assessment; however, its accuracy is greatly affected by corneal irregularities [1]. Tono-Pen and pneumatonometer, which have a smaller contact area, may be more useful in such patients; however, even these tools have limited use when extensive corneal pathology is present.…”

“…Despite the numerous modalities of applanation currently available, intraocular pressure (IOP) estimation remains a challenge when corneal thickness and surface irregularities are present [1]. Goldmann applanation tonometry (GAT) remains the gold standard for IOP assessment; however, its accuracy is greatly affected by corneal irregularities [1].…”