Dynamic Contour Tonometry eliminates most of the systematic errors arising from individual changes of corneal properties that adversely influence all types of applanation tonometers. The advantage of measuring the true pressure in combination with the capability of registering dynamic pressure fluctuations discloses new tonometric opportunities to diagnose and classify different types of glaucoma.

Dynamic contour tonometry (DCT) is a new technology for noninvasive and direct measurement of intraocular pressure (IOP); its results are thought to be influenced less than those of other methods by structural characteristics of the eye. The curvature of the pressure sensing device is concave and only slightly flatter than that of the human cornea. The cornea adapts to the curvature of the transducer head, and the sensor in the centre of the adapted area measures the pressure on the other side of the cornea in the force-free range. Studies published so far suggest that DCT is less heavily dependent than applanation tonometry on the biomechanical properties of the cornea . A further advantage of DCT over other forms of tonometry is the capability of dynamic measurements over time. It is also possible to measure both the diastolic and the systolic IOD and determine the difference between the two, i.e. the ocular pulse amplitude (OPA). OPA is an indirect indicator of choroidal perfusion and reflects the condition of the arterial vascular system and the action of the heart. It could be important in the diagnosis and treatment of glaucoma.

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ABSTRACT.Purpose: We present a prototype of the hand-held dynamic contour tonometer (HH-DCT) and prospectively compare this HH-DCT with the well-established Perkins applanation tonometer (PAT) and the TonoPenXL (TPXL). Methods: In a prospective, single-centre, randomized study, intraocular pressure (IOP) readings were taken in random order using HH-DCT, PAT and TPXL tonometers. Intra-observer variability was calculated for each observer and compared between three experienced ophthalmologists and an inexperienced medical student. Results: Ninety-two corneas of 92 healthy participants were enrolled. IOP [mean mmHg ± standard deviation (SD)] as measured by HH-DCT was 16.97 ± 2.71, by PAT 13.98 ± 2.52 and by TPXL 13.34 ± 2.68. The range of three consecutive IOP readings differed significantly between the devices [p < 0.001; mean range: 1.45 ± 1.07 (HH-DCT), 1.87 ± 0.97 (PAT) and 2.08 ± 1.77 (TPXL)]. There was no difference of the range in all devices between the ophthalmologists and the medical student (HH-DCT p = 0.68, PAT p = 0.54, TPXL p = 0.48). Conclusion: IOP readings measured by HH-DCT are significantly higher than by PAT and TPXL. The differences of IOP measurements are in good accordance with previous studies using the slit-lamp-mounted DCT (SL-DCT) and Goldmann Applanation Tonometry, where SL-DCT readings were 1-3.2 mmHg higher. HH-DCT seems to give more constant results, which can be seen in the lower intra-observer variability compared to PAT and TPXL.

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).

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 constructed a contact lens with an integrated pressure-sensing device. It is housed in a container with three force-sensing elements, each 120 degrees apart, enabling measurement of the appositional force, i.e., the force with which the instrument is held against the eye. In part 1 of the study, the lens' precision was tested against a manometric transducer in five eye bank eyes. The second part examined pressure as a factor dependent on the appositional force, and the third part of the study investigated the correct procedure for measuring baseline eye pressure, p0. The instrument described here allows investigation of three examination parameters: (a) the measurement of p0, the pressure independent of the appositional force; (b) the continuous measurement of the intraocular pressure (IOP); (c) the measurement of the IOP dependent on the appositional force, including artificial IOP elevation.

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.