WO2025026807A1 - Pressure-adjustable test eye for tonometers - Google Patents

Abstract

The present solution relates to a pressure-adjustable test eye for tonometers, in particular for contactless tonometers. The proposed pressure-adjustable test eye for tonometers consists of a base element with a pressure source, at the edge of which base element a film, simulating the cornea, is fastened, the resulting cavity being filled with liquid or gas. According to the invention, the film simulating the cornea has, starting from a central, mechanically excitable region, gradually varying conducting properties for mechanical waves. For simulation of the cornea, a film is used which is self-supporting and has a certain residual stiffness. The pressure-adjustable test eye is intended for tonometers, in particular contactless tonometers, in order to generate the most realistic measurement signals possible, in order to be able to carry out regular function tests and/or calibrations. However, the pressure-adjustable test eye can also be used in elastography or elastometry in order, for example, to enable a pre- and postoperative evaluation of corneas to be carried out.

Description

Pressure-adjustable test eye for tonometer

The present invention relates to a pressure-adjustable test eye for tonometers, in particular for contact-free tonometers. Test eyes are essentially used to regularly check and/or calibrate medical devices for their correct function.

A tonometer is used to measure the intraocular pressure (IOP). An increase above the normal value is usually one of the most important, but not the only, risk factor for glaucoma. Lowering the IOP, for example through medication (eye drops or drug depot implants) or surgical interventions, is the most important therapeutic measure for treating glaucoma, which is why tonometric monitoring of the IOP is an important tool for managing therapy. However, glaucoma can also be present when the intraocular pressure is within the normal range mentioned above (normal pressure glaucoma), and increased intraocular pressure outside the normal range (hypertension) only gives rise to suspicion of a disease.

Glaucoma, also known as glaucoma, is a group of eye diseases of various causes that result in irreversible damage to the nerve fibers of the optic nerve. As the disease progresses, this becomes noticeable at the point where the optic nerve exits as increasing hollowing (excavation) or fading and atrophy of the optic nerve head (papilla). This results in characteristic visual field defects (scotomas), which in extreme cases can lead to blindness in the affected eye.

Increased intraocular pressure can be measured regularly in a simple manner, for which various solutions are known according to the state of the art. For the sake of completeness, it should be noted that the usual The stated intraocular pressure (IOP) is the relative pressure of the inside of the eye, particularly the aqueous humor, in relation to the atmospheric air pressure. If this relative pressure is significantly increased, for example, the eye becomes noticeably hard, which is why ophthalmologists used palpation to at least qualitatively assess the intraocular pressure before tonometers were available. However, absolute pressures, such as those determined by intraocularly implanted pressure sensors, must be distinguished from this IOP if they are not related to the prevailing atmospheric air pressure.

Tonometers for determining intraocular pressure are important diagnostic devices in ophthalmology, especially for the detection of ocular hypertension as a major risk factor for glaucoma and for therapy monitoring, but also in emergency medicine for the detection of high intracranial pressures that are transmitted to the eye.

Tonometers, as medical devices, should be regularly checked for correct functioning and/or must be calibrated. Unfortunately, this is a difficult task, as the pressure-dependent interaction of an eye with the respective tonometer is complex and different pressure levels must be tested. This is a largely unsolved problem, especially for dynamic measuring, contact-free tonometers, such as airpuff or rebound tonometers or the shock wave tonometer described in [1].

In the state of the art, solutions are known in which substitutes are used that simulate, for example, the reaction of an eye to be measured without contact by tonometry.

US 2014/0323843 A1 describes a tool for calibrating a non-contact tonometer (NCT). The tonometer calibration tool consists of a non-contact tonometer, which is placed in front of an air outlet channel of a non-contact tonometer. Tonometer's positionable "electronic eye" with a pressure sensor to receive the air pulse and a transmitter to provide a pseudo-applanation event.

In particular, the electronic eye is used to simulate the reaction of an eye that is to be measured tonometrically without contact by imitating a pressure-dependent deflection of a light reflex on a "cornea" that is dynamically deformed by an air puff. However, the light beam is not actually deflected, but a similar light signal is generated depending on the air puff, which is detected by the air-puff tonometer instead of the deflected light beam.

It is obvious that this tool cannot be used to test the full functionality of the tonometer, since the measuring beam of the tonometer is not actually deflected.

From the state of the art, no calibration check is known for rebound tonometers.

This applies to both the Tono-Vera rebound tonometer from Reichert and the I-Care from Revenio. As a result, there are no known calibration or test eyes that can simulate realistic, intraocular pressure-dependent behavior, which can be used to check measurements that are dependent on intraocular pressure.

In [1], experiments were reported for shock wave and rebound tonometry using a phantom eye consisting of a film stretched over a cylinder. It is stated that different film materials and thicknesses were tested and that ultimately a 50 pm thick TPU film provided the most useful results. This phantom eye was also subjected to a pressure in the range of 10 ... 70 mmHg, which was adjustable via a manometer. However, a comparison of the signal curves shown in this publication for this eye phantom and a pig eye model shows that the signals at the phantom eye have a significantly different structure from the signals in the biological sample (many oscillations and lower damping behavior

In this regard, reference is made to the article [1], which compares, among other things, the signal curves of shock wave tonometric measurements on a cylindrical phantom eye with a screw-on ring and on a pig's eye.

The state of the art also describes solutions for “test eyes” for non-tonometric applications.

According to [2], artificial anterior chambers are known that can be used for surgical manipulation of corneas or for training purposes.

The chamber is a special device that allows a donor's corneoscleral tissue cap to be positioned anatomically with the epithelial side up. The chamber is used to support the donor tissue and maintain adequate pressure while lamellar dissection or full-thickness trephination is performed on the donor tissue.

However, our own experiments with such an artificial anterior chamber using corneal replacement materials have shown that the tonometric signals obtained were not sufficiently usable. This led to the suspicion that the unnatural way in which the corneal replacement material is held in place (local pressing in) and the associated abrupt transition to the hard chamber material are the cause of the problem. For further experiments, a test eye (artificial eye) that was anatomically correct in certain aspects and is used in particular for surgical training was used. Although this test eye had a particularly realistic corneal thickness of 0.5 mm (central) to 0.8 mm (peripheral) and an 8 mm "dilated" pupil, even after modification for pressure application, the results were still unsatisfactory.

Literature:

[1] https://doi.Org/10.1371 /journal, pone.0227488

[2] https://bpic.com/products/barron-artificial-anterior-chamber/

[3] https://d0i.0rg/l 0.1371 /journal, pone.0227488

[4] https://www.innoform-coaching.de/blog/2021/06/07/was-sind-eigentlich- pe-ld-pe-hd-pe-lld-und-ldpe-qenau/)

The present invention is based on the object of providing a test eye to enable intraocular pressure-dependent measurements, in particular for dynamically measuring, contact-free tonometry methods. In particular, the test eye should be used to generate measurement signals that are as close to reality as possible in order to be able to carry out regular functional tests and/or calibrations.

This object is achieved with the proposed pressure-adjustable test eye for tonometers, in particular for contact-free tonometers, consisting of a base element with a pressure source, to the edge of which a film simulating the cornea is attached, the resulting cavity being filled with liquid or gas, in that the film simulating the cornea has gradually varying conduction properties for mechanical waves, starting from a central, mechanically excitable region. Preferred further developments and advantageous embodiments are the subject of the dependent claims and essentially relate to the film which simulates the cornea and is attached to the edge of the base element.

According to a first embodiment, the film simulating the cornea has a flat or curved surface, the central, mechanically excitable region of which has an area between 500 and 8000 mm ² .

According to a second advantageous embodiment, the film simulating the cornea has a homogeneous, isotropic structure and is transparent and elastic.

According to a third advantageous embodiment, the inner and outer sides of the film are smooth and contain no mechanical disturbances, so that a low optical and acoustic scattering effect is achieved.

According to a fourth advantageous embodiment, the film simulating the cornea consists of PVC, TPU or PE, in particular PE-LD.

Further preferred developments relate to the design of the gradually varying conduction properties of the film for mechanical waves by property modification. In particular, the property modification includes a variation of the curvature and/or a variation of the thickness and/or a variation of the elasticity of the film simulating the cornea.

According to a last preferred development, a damping element is present directly under the film simulating the cornea, which is designed and arranged in such a way that the central, mechanically excitable area has a minimum distance from the damping element of 10 to 2000pm, in particular 500 to 800pm. Particularly preferably, the film and the damping element located directly underneath gradually approach each other, whereby the approach decreases particularly preferably from the inside to the outside.

In order to avoid asymmetric deformations caused by gravity for all the above-mentioned designs, the test eye is arranged for measurements so that the base element is aligned horizontally and the film simulating the cornea points upwards or downwards. However, it is also possible to carry out the property modification of the film simulating the cornea in such a way that the test eye is not unacceptably deformed by gravity under measurement conditions.

The proposed pressure-adjustable test eye is intended for tonometers, in particular for non-contact tonometers, in order to generate measurement signals that are as close to reality as possible in order to perform regular functional tests and/or calibrations.

However, the proposed pressure-adjustable test eye is not only applicable for tonometry, but also for elastography or elastometry, for example to enable the pre- and postoperative evaluation of corneas.

The invention is described in more detail below using exemplary embodiments. In this regard:

Figure 1 : a pressure-adjustable test eye with a flat foil,

Figure 2: a pressure-adjustable test eye with a curved foil,

Figure 3: a pressure-adjustable test eye with a foil with varied

Curvature, Figure 4: a pressure-adjustable test eye with a foil of varying thickness,

Figure 5: a pressure-adjustable test eye with a damping element arranged under the foil and

Figure 6: a pressure-adjustable test eye with a foil with varying curvature, varying thickness and a damping element.

The proposed pressure-adjustable test eye for tonometers, in particular for contact-free tonometers, consists of a base element with a pressure source, to the edge of which a film simulating the cornea is attached, the resulting cavity being filled with liquid or gas.

Since it is in principle possible for the base element and the film simulating the cornea to be manufactured in one piece, this variant will also be included in the following description.

According to the invention, the film simulating the cornea has gradually varying conduction properties for mechanical waves, starting from a central, mechanically excitable area. According to the invention, a film is used to simulate the cornea which is self-supporting and has a certain residual rigidity.

The central, mechanically excitable area is the area of the foil that is to be stimulated by a tonometer to be tested, for example by an air blast, in order to generate measurement signals that are as realistic as possible.

Water, silicone oil or similar can be used as a liquid for the cavity. It is also possible to fill the test eye partially or completely with gas, for example to test the measuring conditions in a partially gas-filled patient eye. Gas fillings, for example with the very dense but non-toxic sulphur hexafluoride, are used in the treatment of retinal detachments, among other things. Since sulphur hexafluoride is chemically inert, it can also be used in a test eye.

For the sake of simplicity, the film that simulates the cornea is referred to below as just the film.

According to the invention, the base element holding the film is plate-shaped or cylindrical, with its diameter being larger than its height. Preferably, the base element also has at least one pressure sensor to detect the pressure setting of the test eye. The pressure sensor is advantageously designed in such a way that it can carry out a relative pressure measurement to the atmospheric ambient pressure, for example by means of a can or membrane barometer that is measurably deformed by the pressure difference between the test eye fluid and the ambient pressure. Alternatively, an absolute measuring pressure sensor (for example as a temperature-compensated, miniaturized MEMS or piezoresistive sensor) can be used in the test eye, although a second pressure sensor is then required to determine the atmospheric ambient pressure as a reference value. Another variant is to pair these two sensors in a pressure sensor module that emits a differential electrical measurement signal for the relative pressure in the test eye.

Figure 1 shows a first pressure-adjustable test eye consisting of a cylindrical base element 1.1 with a pressure source 2, to the edge of which a flat film 3.1 is attached. The resulting cavity 4 is filled with liquid or gas, which is indicated by the hatching. Pressure sensors are not shown for the sake of clarity. In contrast, Figure 2 shows a second pressure-adjustable test eye consisting of a flat base element 1.2 with a pressure source 2, to the edge of which a curved film 3.2 is attached. The resulting cavity 4 is filled with liquid or gas, which is expressed by the hatching.

Preferred further developments and advantageous embodiments essentially concern the film attached to the edge of the base element.

According to a first embodiment, the film simulating the cornea has a flat or curved surface. This can, for example, have the shape of a sphere or an ellipsoid. The central, mechanically excitable region of the film particularly preferably has an area of between 500 and 8000mm ² .

According to a second advantageous embodiment, the film simulating the cornea has a homogeneous, isotropic structure that is preferably transparent and elastic. It is particularly advantageous if the film is also optically reflective, with a degree of reflection between 0.1 and 10%. This average reflectivity should be related to vertically incident, non-polarized light. Changes in reflectivity can be achieved by suitable surface coatings. Alternatively, reductions in film rear-side reflections can also be reduced by introducing dyes that absorb the measuring radiation on the way to the rear of the film and back.

According to a third advantageous embodiment, the inner and outer sides of the film are smooth and contain no mechanical disturbances, so that a low optical and acoustic scattering effect is achieved.

According to a fourth advantageous embodiment, the film simulating the cornea consists of PVC, TPU or PE, in particular PE-LD. This Materials have proven to be particularly suitable for generating measurement signals that are as realistic as possible.

In principle, other variants of PE films can also be used, such as PE-VLD, PE-LD, PE-MD, PE-HD (from “very low density”, “low density”, “medium density”, “linear low density” to “high density”). Regarding the variants of PE films, please refer to article [4].

The further preferred developments relate to the design of the gradually varying conduction properties of the film for mechanical waves by property modification. In particular, the property modification includes a variation in the curvature and/or a variation in the thickness and/or a variation in the elasticity of the film simulating the cornea. Property modification of the film is understood here to mean, for example, deep-drawing the film during the manufacturing process, whereby the curvature is flattened somewhat in the center.

Figure 3 shows a third pressure-adjustable test eye consisting of a flat base element 1.2 with a pressure source 2, to the edge of which a curved foil 3.3 is attached. The resulting cavity 4 is also filled with liquid or gas, which is expressed by the hatching. In particular, the gradually varying conduction properties for mechanical waves were generated by varying the curvature of the curved foil 3.3.

Figure 4 shows a fourth pressure-adjustable test eye consisting of a flat base element 1.2 with a pressure source 2, to the edge of which a curved foil 3.4 is attached. The resulting cavity 4 is also filled with liquid or gas, which is again expressed by the hatching. In particular, the gradually varying conduction properties for mechanical waves in this variant were generated by varying the thickness of the curved foil 3.4. Preferably, the film has a thickness in the range between 10 and 1000 pm.

Another possibility for producing gradually varying conduction properties for mechanical waves is to vary the elasticity of the film, for example by local stretching, thermal or chemical treatment or coating. According to the invention, the film has a modulus of elasticity in the range from 0.2 to 1000 MPa, in particular in the range below 10 MPa.

According to a last preferred development, a damping element is present directly under the film simulating the cornea, which is designed and arranged such that the central, mechanically excitable area has a minimum distance from the damping element of 10 to 2000pm, in particular 500 to 800pm. In addition, a possibility for pressure equalization can be provided in the damping element.

Figure 5 shows a fifth pressure-adjustable test eye consisting of a flat base element 1.2 with a pressure source 2, to the edge of which a curved film 3.5 is attached. The resulting cavity 4 is also filled with liquid or gas, which is expressed by the hatching. In particular, a damping element 5 with a pressure compensation element in the form of an opening 5.1 is arranged under the curved film 3.5.

Particularly preferably, the film and the damping element located immediately underneath it gradually approach each other, with the approach particularly preferably decreasing from the inside to the outside.

Figure 6 shows a sixth pressure-adjustable test eye consisting of a planar base element 1.2 with a pressure source 2, a curved foil 3.6 is attached to the edge. The resulting cavity 4 is again filled with liquid or gas, which is indicated by the hatching. A damping element 5 is also arranged under the curved foil 3.6. In particular, the gradually varying conduction properties for mechanical waves in this variant were generated by varying the thickness and curvature of the curved foil 3.6 and the varying distance of the damping element.

According to the invention, a sufficiently slow, gradual approach between the film and the damping element in the peripheral direction is required, whereby a defined distance must be maintained in order to avoid signal interference.

The damping element can also be designed in such a way that the film and the damping element touch or are connected outside the central, mechanically excitable area.

According to the invention, the film and the damping element preferably have different mechanical properties.

According to a further embodiment, the damping element arranged directly beneath the film simulating the cornea can be integrated into the base element.

The foil is located at a defined distance from the damping element or gradually approaches it in a peripheral direction until contact occurs. This creates a gradual coupling between the foil and the damping element, which results in a more realistic signal attenuation of the signals generated during contact-free tonometry.

In order to take into account the gravity-induced forces in all the above-mentioned configurations,

To avoid deformations, the test eye for measurements is arranged so that that the base element is aligned horizontally and the film simulating the cornea points upwards or downwards. It is also possible to modify the properties of the film simulating the cornea in such a way that the test eye is not unacceptably deformed by gravity under measurement conditions.

For this purpose, the film could be locally stiffened or pre-formed in such a way that the desired shape of the test eye is still ensured in the end, despite the additional deformation caused by gravity that occurs under measurement conditions.

The present invention provides a test eye that enables measurements dependent on the intraocular pressure, in particular for dynamically measuring, contact-free tonometry methods. In particular, the test eye generates realistic measurement signals in order to be able to carry out regular functional tests and/or calibrations.

The test eye described comes very close to the behavior of the human eye, particularly in the area of the anterior chamber (cornea, iris and limbus) in terms of mechanical excitation and vibration behavior. The interaction of the foil and the damping element makes it possible to simulate the slight reflection of surface waves at the edge of the cornea of the real eye.

The proposed pressure-adjustable test eye is intended for tonometers, especially for non-contact tonometers, but can also be used for elastography or elastometry.

Claims

patent claims 1. Pressure-adjustable test eye for tonometers, in particular for contact-free tonometers, consisting of a base element with a pressure source, to the edge of which a film simulating the cornea is attached, the resulting cavity being filled with liquid or gas, characterized in that the film simulating the cornea, starting from a central, mechanically excitable region, has gradually varying conduction properties for mechanical waves and that a damping element is present directly below the film simulating the cornea. 2. Pressure-adjustable test eye according to claim 1, characterized in that the base element is plate-shaped or cylindrical, wherein its diameter is greater than its height. 3. Pressure-adjustable test eye according to claim 1, characterized in that the central, mechanically excitable region of the film simulating the cornea has an area between 500 and 8000mm ² . 4. Pressure-adjustable test eye according to claim 1, characterized in that the film simulating the cornea has a homogeneous, isotropic structure. 5. Pressure-adjustable test eye according to claim 1, characterized in that the film simulating the cornea is transparent and elastic. 6. Pressure-adjustable test eye according to claim 1, characterized in that the film simulating the cornea has an optically reflective effect, with a reflection factor between 0.1 and 10%. 7. Pressure-adjustable test eye according to claim 1, characterized in that the film simulating the cornea consists of PVC, TPU or PE, in particular PE-LD. 8. Pressure-adjustable test eye according to claim 1, characterized in that the gradually varying conduction properties for mechanical waves were achieved by modifying the properties of the film simulating the cornea. 9. Pressure-adjustable test eye according to claim 8, characterized in that the property modification of the film simulating the cornea includes a variation of its curvature and/or a variation of its thickness and/or a variation of its elasticity. 10. Pressure-adjustable test eye according to claim 8, characterized in that the film simulating the cornea has a thickness in the range between 10 and 1000 pm. 11. Pressure-adjustable test eye according to claim 8, characterized in that the elasticity of the film simulating the cornea has a modulus of elasticity in the range of 0.2 to 1000 MPa, in particular in the range below 10 MPa. 12. Pressure-adjustable test eye according to claim 1, characterized in that the damping element is designed and arranged such that the central, mechanically excitable region has a minimum distance from the damping element of 10 to 2000pm, in particular 500 to 800pm. 13. Pressure-adjustable test eye according to claim 12, characterized in that the film simulating the cornea and the damping element located immediately underneath gradually approach each other. 14. Pressure-adjustable test eye according to claim 12, characterized in that the minimum distance between the central, mechanically excitable region of the film simulating the cornea and the damping element decreases from the inside to the outside. 15. Pressure-adjustable test eye according to claim 12, characterized in that the film simulating the cornea and the damping element can touch or be connected outside the central, mechanically excitable region. 16. Pressure-adjustable test eye according to claim 12, characterized in that a possibility for pressure equalization is provided in the damping element located immediately beneath the film simulating the cornea. 17. Pressure-adjustable test eye according to claim 12, characterized in that the film simulating the cornea and the damping element arranged underneath have different mechanical properties. 18. Pressure-adjustable test eye according to claim 12, characterized in that the damping element arranged directly under the film simulating the cornea is integrated into the base element. 19. Pressure-adjustable test eye according to claim 1, characterized in that the test eye is arranged for measurements so that the base element is aligned horizontally and the membrane simulating the cornea points upwards or downwards, so that asymmetric deformations caused by gravity are avoided. 0. Pressure-adjustable test eye according to claim 8, characterized in that the property modification of the film simulating the cornea was carried out in such a way that the test eye is not unacceptably deformed by gravity under measurement conditions.