Ein Prototyp einer Kontaktlinse (KL-DCT), basierend auf der dynamischen Konturtonometrie („dynamic contour tonometry“, DCT), wurde zur kontinuierlichen Augeninnendruckmessung entwickelt. Ziel dieser Pilotstudie ist es, die Anwendbarkeit dieser KL-DCT aufzuzeigen.

BackgroundA prototype of a pressure-sensitive contact lens (CL-DCT) based on dynamic contour tonometry (DCT) has been developed for continuous intraocular pressure (IOP) monitoring. The purpose of the present study was to assess the clinical applicability of this CL-DCT.Material and MethodsIn 24 healthy subjects continuous IOP recording with the CL-DCT for 100 s was accomplished including IOP monitoring during 2 consecutive Valsalva manoeuvres. The measurement procedure was repeated after 5 min on the same eye and compared with the initial measurement.ResultsContinuous pressure curves were recorded in 20 subjects. The CL-DCT revealed an individual increase in IOP from 0.74 to 8.26 mmHg during the Valsalva manoeuvres. Comparison of the 2 consecutive IOP measurements yielded a mean deviation of ±0.4 mmHg.ConclusionsCL-DCT allows non-invasive and continuous measurements of IOP. The measured values are comparable to the expected ones. Further studies are necessary to compare the measurement accuracy of CL-DCT with that of slit lamp adapted DCT (SL-DCT).

BACKGROUND:A prototype of a pressure-sensitive contact lens (CL-DCT) based on dynamic contour tonometry (DCT) has been developed for continuous intraocular pressure (IOP) monitoring. The purpose of the present study was to assess the clinical applicability of this CL-DCT.MATERIAL AND METHODS:In 24 healthy subjects continuous IOP recording with the CL-DCT for 100 s was accomplished including IOP monitoring during 2 consecutive Valsalva manoeuvres. The measurement procedure was repeated after 5 min on the same eye and compared with the initial measurement.RESULTS:Continuous pressure curves were recorded in 20 subjects. The CL-DCT revealed an individual increase in IOP from 0.74 to 8.26 mmHg during the Valsalva manoeuvres. Comparison of the 2 consecutive IOP measurements yielded a mean deviation of +/-0.4 mmHg.CONCLUSIONS:CL-DCT allows non-invasive and continuous measurements of IOP. The measured values are comparable to the expected ones. Further studies are necessary to compare the measurement accuracy of CL-DCT with that of slit lamp adapted DCT (SL-DCT).

A prototype of a pressure-sensitive contact lens (CL-DCT) based on dynamic contour tonometry (DCT) has been developed for continuous intraocular pressure (IOP) monitoring. The purpose of the present study was to assess the clinical applicability of this CL-DCT.In 24 healthy subjects continuous IOP recording with the CL-DCT for 100 s was accomplished including IOP monitoring during 2 consecutive Valsalva manoeuvres. The measurement procedure was repeated after 5 min on the same eye and compared with the initial measurement.Continuous pressure curves were recorded in 20 subjects. The CL-DCT revealed an individual increase in IOP from 0.74 to 8.26 mmHg during the Valsalva manoeuvres. Comparison of the 2 consecutive IOP measurements yielded a mean deviation of +/- 0.4 mmHg.CL-DCT allows non-invasive and continuous measurements of IOP. The measured values are comparable to the expected ones. Further studies are necessary to compare the measurement accuracy of CL-DCT with that of slit lamp adapted DCT (SL-DCT).

Das dynamische Konturtonometer ist das erste und einzige nichtinvasiv, kontinuierlich und direkt messende Tonometer. Durch Aufsetzen des drucksensiblen Tonometerköpfchens wird die Hornhaut schonend in die Form gebracht, die sie natürlicherweise annimmt, wenn der Druck auf beiden Seiten gleich ist. Zwischen Tonometerköpfchen und Hornhaut entsteht ein Kräftefeld, das genau dem Augeninnendruck entspricht. Ein in die Kontaktfläche integrierter piezoresistiver Drucksensor misst kontinuierlich und präzise den Augeninnendruck und erfasst auch dessen zeitliche Schwankungen als okuläre Pulsamplitude (OPA). Die Abhängigkeit des Tonometers von den biomechanischen Parametern der Hornhaut ist deutlich geringer als bei den herkömmlichen, auf Applanation oder Indentation beruhenden Messverfahren.

The dynamic contour tonometer (DCT) is the first and only noninvasive contact tonometer that is capable of measuring intraocular pressure (IOP) directly and continuously. The touch of the pressure-sensitive tonometer tip induces the cornea to gently assume a shape (contour) which it will naturally assume when pressure on both sides is equal. A force field establishes between tonometer tip and cornea, that corresponds exactly to IOP. A piezoresistive pressure sensor, integrated into the surface of the tonometer tip, precisely measures IOP continuously and therefore also records time-dependent modulations of IOP as "ocular pulse amplitude" (OPA). Dependence of the DCT on biomechanical properties of the cornea is substantially smaller than with traditional tonometers that applanate or indent the cornea.

We read with great interest the article by Siganos and coauthors1 about dynamic contour tonometry (DCT). Our studies also strongly suggest that contour-matching tonometry is less dependent on corneal rigidity than applanation tonometry. However, we want to clarify that in the article, our studies were cited incorrectly and we did not use noncontact air tonometry. In a comparative study of human cadaver eyes,2 we compared the recently introduced dynamic contour tonometer and manometric reference pressure. We concluded that at all intraocular pressure (IOP) levels (5 mm Hg to 58 mm Hg), DCT readings were significantly closer to the real intracameral IOP than both pneumatonometry and Goldmann applanation tonometry. Unfortunately, it was not possible to correlate IOP readings with corneal thickness since human cadaver corneas are structurally altered and extremely hydrated starting very shortly after death. However, in the study cited in the text (Kniestedt et al.), we compared tonometers at varying stages of corneal hydration.3 We performed DCT measurements on maximally hydrated and dehydrated eyes and found that DCT appears to be independent of corneal thickness changes produced by altering corneal hydration. This is clinically relevant since corneal edema is a relatively frequent occurrence and accurate IOP measurements are necessary to determine causation and management. Thus, corneal thickness as an inherited trait was not and could not be examined in any of our cadaver eye studies and citing our studies as having determined this is incorrect. The second citation in our article (Kanngiesser et al.) refers to a study in which we described the theoretical model and compared the mathematical and geometrical results with actual DCT readings in cadaver eyes. It is true that within the limited boundaries of the in vitro study, corneal thickness (chemically thinned), corneal astigmatism, and corneal radius do not seem to influence the accuracy of DCT. To draw any conclusion that in a clinical setting DCT is independent of innate corneal thickness would not be accurate. That DCT may actually be independent of corneal thickness was suggested by a recently completed clinical study using DCT and applanation tonometry, in which no correlation between corneal thickness and DCT readings was found, whereas applanation tonometry according to Goldmann was indeed correlated with central corneal thickness.4 Proof that DCT is independent of corneal thickness can only be obtained by comparing DCT to manometric readings in living, normal eyes—a study that would be difficult to perform.5–7 Christoph Kniestedt MD Hartmut Kanngiesser PhD Robert L. Stamper MD aWintherthur, Switzerland bPort, Switzerland cSan Francisco, California, USA

The dynamic contour tonometer (DCT) is the first and only noninvasive contact tonometer that is capable of measuring intraocular pressure (IOP) directly and continuously. The touch of the pressure-sensitive tonometer tip induces the cornea to gently assume a shape (contour) which it will naturally assume when pressure on both sides is equal. A force field establishes between tonometer tip and cornea, that corresponds exactly to IOP. A piezoresistive pressure sensor, integrated into the surface of the tonometer tip, precisely measures IOP continuously and therefore also records time-dependent modulations of IOP as "ocular pulse amplitude" (OPA). Dependence of the DCT on biomechanical properties of the cornea is substantially smaller than with traditional tonometers that applanate or indent the cornea.

PURPOSE To establish a standard clinical procedure for measuring intraocular pressure (Po) with the contact lens tonometer (CLT), to demonstrate possibilities for analyzing ocular pulsation and performing ophthalmodynamometry. METHODS A reliable histogram-based analyzing system for determining Po is used. First, the ocular pressure was registered with the CLT method and compared with the Goldmann applanation pressure, measured immediately beforehand. Second, ocular pulsation was studied by recording Po for 30 to 70 seconds, and the pulse amplitude was then analyzed. Third, an ophthalmodynamometry method during slit-lamp examination was tested. The central retinal artery was observed through the contact lens while the appositional force was elevated. A mark was set at the systolic and diastolic pressure while observing arterial pulsation (similar to the Korotkoff sounds). RESULTS Compared with the Goldmann method measurements, Po obtained with the CLT method yielded a linear regression of r = 0.7 (right eye) and r = 0.68 (left eye), and was therefore highly significant (P < 0.0001, two-tailed). Analysis of the pulse amplitude showed great variability (range, 1 to 9 mm Hg; means, 2.9 mm Hg [right eye] and 3.0 mm Hg [left eye]). The dependence of the pulse amplitude on Po and age was shown with a correlation coefficient of r = 0.55 and r = 0.59, respectively. The difference between the right and left eye of the person was < 0.5 mm Hg. CONCLUSION The CLT can be used during slit-lamp examination and permits tonometry during ophthalmoscopy, ocular pulsation assessment at different intraocular pressures, and ophthalmodynamometry.

This paper present a tonometer incorporated in a contact lens, which allows simultaneous measurement of intraocular pressure and performance ophthalmoscopy. The tonometer can record the pulse curve continuously, which can give us an indication of any circulatory problem. The device is therefore expected to yield additional information useful for the diagnosis of early glaucoma. Te device has three force sensors built in, which allow continuous measurement of the force exerted on the eye surface by the contact lens. The force of the contact lens on the eye can be altered and makes the adjustment of different eye pressures possible. These induced changes of the eye pressure and their influence on the fundus can be checked. We have taken some measurements on enucleated human eyes to compare our device with a Statham tansducer in the vitreous. We found a good correlation. We are currently taking measurements in volunteers. The clinical relevance of these observations and measurements will be examined in a future study.

Background This paper presents a tonometer built into a contactlens, which allows to measure the eye-pressure and to perform ophthalmoscopy at the same time. Artificially induced changes of the eye-pressure and their influence on the visible fundus can now be checked simultanously. The contactlens-tonometer (CGT) also is able to record continuously the pulse-curve, which can indicate any circulatory problem. So, the device is expected to give us additional diagnostic criteria of early glaucoma. Each ophthalmologyst in the field will be able to preform with this device a oculodynamometry in an easy way. By this it is possible to estimate the pressure-tolerance of the optic disk from glaucoma-patients.Measurements There have been taken some measurements on enucleated human eyes, comparing our device with a Stat-ham-transducer in the vitreous. We found a good correlation. In a second step, we made measurements (65) on healthy volunteers, comparing the device with Perkins-Tonometry.Results and conclusions We found a correlation (R=0.58). The error of the measurements was about +/- 3 mm Hg. Considering both, the deviation of the Perkins-Tonometer with which our results were compared, and the fact of a good correlation (R=0.999) in the study with the enucleated human eyes, we found that the contact-lens-tonometer measures the intraocular pressure exactly. In future studies, we want to analyze the dynamic component of the measurements.