Contactless Tonometer

Abstract

The present invention relates to a tonometer for measuring intraocular pressure, wherein the examination is carried out without direct contact with the eye. The proposed non-contact tonometer consists of a device base, an excitation source movable relative to the device base, a sensor and a central control unit. According to the invention, the excitation source is connected to the device base via a positioning unit and has a distance sensor rigidly connected to it. The distance sensor and the positioning unit are interconnected and configured to maintain minimum distances between the excitation source and eye structures. The central control unit has connections to the excitation source and the sensor and is configured to determine the intraocular pressure from the sensor's measurement data. The proposed solution is specifically designed for a tonometer for non-contact measurement of intraocular pressure. However, the principle can also be applied to other ophthalmic devices, particularly handheld ones.

Description

[0001] The present invention relates to a tonometer for measuring intraocular pressure, wherein the examination is carried out without direct contact with the eye.

[0002] Glaucoma, also known as open-angle glaucoma, refers to a group of eye diseases with varying causes that, if left untreated, result in irreversible damage to the nerve fibers of the optic nerve. In advanced stages, this manifests at the optic nerve head as progressive cupping (excavation) or pallor and atrophy of the optic nerve head (optic disc). Consequently, characteristic visual field defects (scotomas) develop, which in extreme cases can lead to blindness in the affected eye.

[0003] Elevated intraocular pressure (IOP) is one of the most important risk factors for glaucoma and can be easily and regularly measured. Various methods are available for this purpose. For the sake of completeness, it should be noted that the commonly reported IOP is the relative pressure of the eye's interior, particularly the aqueous humor, relative to atmospheric pressure. If this relative pressure is significantly elevated, for example, the eye will become noticeably hardened. Therefore, before the availability of tonometers, ophthalmologists used palpation to at least make a qualitative assessment of IOP. However, this IOP should be distinguished from absolute pressures, such as those sometimes determined by intraocularly implanted pressure sensors, when these are not referenced to the prevailing atmospheric pressure (US 8,257,295 B2).

[0004] An early, common, and accurate method for determining intraocular pressure was applanation tonometry, developed by the Austrian-Swiss ophthalmologist Hans Goldmann. This method uses a small measuring device attached to a special ophthalmic examination instrument called a slit lamp. During the examination, the force required to flatten its front surface, which has a diameter of, for example, 3.06 mm (area = 7.35 mm²), is measured. 2The applanation tonometer is used to bring the cornea into contact with the cornea and flatten it. The applied force is generated by a spring scale coupled to a measuring drum. The pressure values ​​can then be read directly from the drum due to the known contact area. To visually verify the contact between the cornea and the measuring device, the examiner can first instill an aqueous solution of the dye fluorescein into the conjunctival sac. There are also handheld applanation tonometers available for examinations of patients, for example, while lying down.

[0005] Applanation tonometers have the significant disadvantage of being a contact method, requiring direct contact with the delicate cornea. This generally necessitates corneal anesthesia. Furthermore, the measurement takes some time during which the patient must remain still to avoid interfering with the measurement or even causing corneal injury. As with other cornea-based tonometry methods, the stiffness, viscoelasticity, and especially the thickness of the cornea can influence the measured pressure values. In individuals with very thick corneas, the measurement may be too high. Conversely, in cases of corneal surgery that reduces corneal thickness, intraocular pressure measurements tend to be too low.

[0006] For correction purposes, it is therefore recommended, especially in certain patient groups, to determine the corneal thickness before measuring intraocular pressure. This is usually done with a pachymeter. The correct value can then be determined using a conversion factor and a correction table.

[0007] An older method, also based on direct contact with the eye, is impression tonometry, for example, using the tonometer developed by the Norwegian ophthalmologist Hjalmar August Schiøtz. The device is placed manually on the anesthetized cornea of ​​the patient, who is lying on their back. It indicates how deeply a metal pin with a defined weight indents the cornea. The intraocular pressure can then be read from a calibrated table.

[0008] One problem with impression tonometry is that the instruments used are only calibrated for eyes with average scleral elasticity and may display incorrect values ​​for intraocular pressure in myopic eyes.

[0009] A new method is Dynamic Contour Tonometry (DCT), whose dynamic measurement principle differs fundamentally from static applanation tonometry because it does not flatten the cornea. Instead, the measuring head, which mimics the cornea's shape, returns it to its natural, tension-free state. The curvature of the cornea under the measuring head is only slightly reduced (flattened). The pressure between the measuring head and the cornea then corresponds to the intraocular pressure. A pressure sensor integrated into the tonometer head can thus measure the intraocular pressure directly and largely independently of corneal influences. The achieved precision allows for the display of intraocular pressure pulse curves, triggered by the heartbeat, similar to an electrocardiogram (ECG).

[0010] In Dynamic Contour Tonometry, corneal thickness has only a minimal influence on the measurement, which is otherwise characterized by high accuracy and reproducibility.

[0011] Among the so-called rebound tonometers is the Icare® ic100 from ICARE FINLAND OY. Its measuring principle is based on a moving, lightweight probe that is accelerated towards the eye, decelerated, and rebounded. The probe's braking and rebound behavior correlates with the intraocular pressure. This braking and rebound behavior is inductively detected by a magnetized wire within the probe. The probe's impact velocity is selected so that the measurement can be taken faster than the blink reflex, thus avoiding interference from patient reactions. Due to the lightweight, rounded probe and the brief impact time, the measurement is often barely perceptible to the patient, so that a local anesthetic is usually unnecessary. To increase measurement accuracy, multiple measurements (e.g., six) are typically performed while the eyelid is open.

[0012] Furthermore, ophthalmodynamometry methods based on tonometry and artificial changes in intraocular pressure (DE 10 2018 107622 A1) are used, in which retinal blood pressures and the resulting perfusion pressures can be determined from pulsation observations of retinal vessels in response to changes in intraocular pressure. These measurements are valuable for a complete glaucoma diagnosis. In some cases, however, ocular perfusion pressures are also approximated using an approximation formula derived from standard blood pressure measurements taken with an upper arm cuff.

[0013] All tonometric measurement principles mentioned so far have the disadvantage that direct contact with the cornea of ​​the eye is required, so either at least a local anesthetic is needed or the patient has to accept at least an unpleasant sensation of contact.

[0014] At least direct contact with the cornea is avoided in transpalpebral scleral tonometry, as the intraocular pressure is measured through the eyelid. The tonometer also works on the recoil principle, with a freely movable rod acting as a sensor when lowered onto the eyelid in the sclera. The patient, whether sitting or lying down, must look upwards at a 45° angle.

[0015] With this method, the results of intraocular pressure measurements also depend on the biomechanical condition of the eyelid and sclera, as well as on the eye's orientation relative to the tonometer. Measurements on the sclera or conjunctiva have the advantage that the sclera and conjunctiva have fewer nerve endings than the cornea and are therefore significantly less sensitive to stimuli (F. Stapelton et al., "Corneal and conjunctival sensitivity to air stimuli", Br J Ophthalmol 2004;88:1547-1551. doi: 10.1136 / bjo.2004.044024). While this method does not require local anesthesia, the patient still perceives direct contact between the eyelid and the probe.

[0016] Airpuff non-contact tonometry (Airpuff NCT) is a method that avoids contact between the eye and the measuring instrument. Intraocular pressure is measured using an air pulse that briefly indents the cornea, for example, by 0.4 to 1 mm within a period of 10 to 30 ms. The measurement accuracy is generally somewhat lower compared to the previously mentioned contact tonometry methods. While impression and applanation tonometry are exclusively performed by ophthalmologists, inspections and screenings of intraocular pressure using Airpuff NCT are increasingly being used by optometrists as well. From the patient's perspective, this measurement method is generally attractive due to its non-contact nature and the absence of local anesthesia, but in practice, the unexpected and clearly perceptible puff of air is occasionally perceived as unpleasant.

[0017] A concrete example of air puff non-contact tonometry is the VISUPLAN® 500 from Carl Zeiss Meditec AG. Its operation is intuitive, allowing the user to select between single and multiple measurements, or a test air pulse, via the touchscreen, with the measurement process then proceeding automatically. The results are displayed directly on the monitor and can also be transmitted or output via a serial interface.

[0018] Another example of air puff non-contact tonometry is the OCULUS CORVIS ST, which, in addition to tonometry, also determines biomechanical properties of the cornea from its rebound behavior during surface deformation by the air puff. This rebound behavior of the cornea is recorded using a high-speed camera at 4330 frames per second.

[0019] The literature describes (Koprowski and Wilczyński, “Re-view Article Corneal Vibrations during Intraocular Pressure Measurement with an AirPuff Method”, Journal of Healthcare Engineering, Volume 2018, Article ID 5705749, https: / / doi.org / 10.1155 / 2018 / 5705749) that a number of surface vibrations can be detected, which also exhibit higher frequency components than the excitation air puff.

[0020] Document US 9,462,947 B2 proposes a solution for non-contact measurement of intraocular pressure using electromagnetic waves. Laser radiation is directed at the ocular surface to generate vibrations or mechanical waves based on photoacoustic phenomena. These surface vibrations are then detected using optical interferometry and / or optical coherence tomography and / or laser Doppler vibrometry to determine intraocular pressure. The document further proposes acquiring additional measurement information, such as corneal curvature and / or thickness and / or the eye's water content, and incorporating this information into the intraocular pressure measurement.

[0021] Another non-contact tonometer is described in US 2016 / 0374554 A1. Using an acoustic or mechanical wave, surface waves of different frequencies are generated in a patient's eye, which are then detected non-contact to obtain intraocular pressure-dependent information about the eye, for example, also using the ultrasound transducers mentioned in the document.

[0022] Document WO 2021 / 160924 A1 proposes yet another optical setup with an array of photodetectors for detecting movements of the ocular surface during contactless measurement of intraocular pressure. Key advantages of the exemplary embodiments described in US 2016 / 0374554 A1 include the fact that no sensitive ocular surfaces need to be touched and, in the contactless design, they can be used from one patient to another with a lower risk of contamination. This also proposes multiple excitation sources near different areas of the sclera, which can excite surface waves on the sclera and cornea, which are then used for pressure-dependent time-of-flight measurements. For generating nonlinear sound waves for contactless surface wave excitation, electrical discharge via spark gaps is specifically proposed.

[0023] While all non-contact tonometry methods have the advantage that no direct contact with the eye surface is necessary, this advantage is associated with increased technical effort to ensure the correct alignment of the measuring unit and sufficient safety by actually avoiding contact.

[0024] For non-contact measurement of intraocular pressure, the excitation sources and sensors often need to be placed very close to the patient's eye, within a distance of 2 mm to 11 mm. This is because otherwise, the excitation pulse would be too widely distributed and its intensity would be significantly reduced as it travels too far to reach the eye. Due to these short distances, uncontrolled movement of the patient and / or the device being moved by the operator can lead to unintentional eye contact with some device designs. This contact can be minimal (eyelashes) or noticeable, even causing injury (sclera, cornea).

[0025] Particular care is required, especially with fresh or healed surgical incisions or wounds.

[0026] To prevent such contact with the eye, the distances between excitation sources and sensors and the eye are detected and / or controlled.

[0027] In current state-of-the-art solutions, excitation sources and sensors for determining the distance are usually positioned at a common point in front of the patient's eye and also directed at the same eye structure. The sensor signals are then used for the common alignment of excitation sources and sensors that are in a fixed spatial relationship to one another.

[0028] Optical sensors are usually used to determine distance and orientation; these sensors detect light reflected from the cornea to visually determine the correct positioning.

[0029] As an example, reference is made here to the solution of an air puff tonometer described in US 3,181,351 A.

[0030] EP 1 402 810 B1 also describes a non-contact tonometer based on the air-puff principle, in which light reflected from the eye (especially corneal reflections) is captured by the measuring system and used for manual or automatic alignment of the device to the eye.

[0031] Another non-contact tonometer based on the air-puff principle is described in US 2020 / 0300236A1. Here, a light source and an optical sensor are used, on the one hand, to determine the correct nozzle distance of an air-puff tonometer relative to the eye, and on the other hand, to detect measurement signals resulting from corneal deformation during the air puff.

[0032] However, a new type of non-contact tonometry now proposes a separation of the excitation source (for the sclera) and the sensors (optical detector for the cornea). Reference is made to WO 2021 / 160924 A1 as an example.

[0033] This means that, firstly, the positions of the excitation source and sensor in relation to the eye can change to different degrees (due to different angles of the measuring and eye axes), and secondly, individual eye shapes and sizes further complicate a common position adjustment for the excitation source and sensors.

[0034] The present invention therefore aims to develop a tonometer for measuring intraocular pressure in which the examination is performed without direct contact with the eye, wherein the excitation source and sensor for pressure measurement can also be directed towards different areas of the eye and yet, even in the case of varying eye sizes and shapes, the risk of eye contact is minimized. Furthermore, the tonometer should be suitable for detecting the excitation distance and for automatically adjusting the excitation distance.

[0035] According to the invention, the object of the non-contact tonometer, consisting of a device base, a excitation source movable relative to the device base, a sensor and a central control unit, is achieved in that the excitation source is connected to the device base via a positioning unit and has a distance sensor rigidly connected to it, that the distance sensor and the positioning unit have connections and are configured to maintain minimum distances of the excitation source to eye structures, and that the central control unit has connections to the excitation source and to the sensor and is configured to determine the intraocular pressure from the measurement data of the sensor.Although the term "sensor" is used in the singular below (which corresponds to the most likely interpretation), it should also include the possibility of using multiple sensors to acquire multiple signals from which IOP values ​​can then be determined. These signals must then be combined into a single, identifiable IOP value (essentially as the measurement result of a single sensor).

[0036] According to a first group of advantageous designs, the tonometric measuring unit is based on air puff or shock wave technology.

[0037] According to a second group of advantageous embodiments, the excitation area of ​​the excitation source is directed towards a first structure of the eye, preferably the sclera, while the measuring area of ​​the sensor is directed towards a second structure of the eye, preferably the cornea. According to a preferred embodiment, at least one further excitation source is provided, which is preferably arranged opposite the first excitation source and has an additional distance sensor and is also connected to the device base via a positioning unit.

[0038] According to a third group of advantageous designs, the distance sensors are optically, capacitively, inductively or ultrasonically based.

[0039] Optical sensors, particularly near-infrared (780–1600 nm) reflective proximity sensors, are preferred, as they can output a distance-proportional signal even at small distances. However, simpler sensors can also be used that only emit an electrical signal when a fixed minimum distance is breached. This signal can then be used to control the positioning unit in a control loop, increasing the distance between the excitation source and the eye until the minimum distance is exceeded again.

[0040] In principle, miniaturized LIDAR or RADAR sensors can also be used as examples of proximity sensors based on other electromagnetic waves, especially for initial rough positioning at large distances.

[0041] According to a preferred embodiment, more than one distance sensor is rigidly connected to an excitation source, the distance sensors preferably being based on at least two different operating principles. According to a particularly preferred embodiment, an additional distance sensor in the form of a camera is arranged at the base of the device to capture frontal images of the eye, in particular of the eyelid, iris, sclera, or eyelashes. Distances can be determined by the camera, for example, by determining the distance-dependent relative size of ocular structures, such as the white-to-white distance for typical anatomical variations, or by using a distance-sensitive camera (3D chip), a stereoscopic camera, or a camera consisting of a 2D or 3D OCT system.

[0042] According to a fourth group of advantageous embodiments, the positioning units are motorized and can be aligned manually or automatically. In particular, the positioning units operate on electromechanical, electromagnetic, piezoelectric, hydraulic, pneumatic, electrothermal, spring-mechanical, or similar principles. According to a preferred further development, the positioning units are configured and controllable in various ways to achieve different minimum distances to the eye.

[0043] According to a fifth group of advantageous embodiments, the positioning unit of the device base is designed to safely minimize the working distance of the excitation source to ocular structures in order to reduce the necessary intensity of the excitation source on the eye. Specifically, the minimum distances of the tonometer to the eye are 0.5 mm to 5 mm or up to 20 mm. The minimum distance should in any case be greater than the thickness of the tear film, which is typically 0.1 mm, and the magnitude of the ocular surface displacement resulting from excitation with the respective excitation sources used (for example, 0.4 to 1 mm in the case of conventional air-puff excitation). The minimum distances between an excitation source and ocular structures from the group "sclera," "conjunctiva," "cornea," "limbus," and "eyelid" are achieved. According to a particularly preferred embodiment, a minimum distance to the eyelashes is not always maintained.

[0044] The proposed solution is specifically intended for a tonometer for non-contact measurement of intraocular pressure to the eye.

[0045] The principle of using stimulation sources and sensors directed at different parts of the eye, which can be positioned independently, can also be applied to other ophthalmic devices where there is a potential risk of eye contact. This is particularly true for handheld ophthalmic devices that lack head rests to minimize uncontrolled patient movements towards the device.

[0046] The invention is described in more detail below with reference to exemplary embodiments. To this end, we show... Fig. 1: a first design variant of the contactless tonometer, Fig. 2: a second design variant of the contactless tonometer, Fig. 3: a third design variant of the contactless tonometer and Fig. 4: a fourth design variant of the contactless tonometer.

[0047] The contactless tonometer consists of a device base, an excitation source that is movable relative to the device base, a sensor and a central control unit.

[0048] According to the invention, the excitation source is connected to the device base via a positioning unit and has a distance sensor rigidly connected to it. The distance sensor and the positioning unit are interconnected and configured to maintain minimum distances between the excitation source and eye structures. The central control unit has connections to the excitation source and the sensor and is configured to determine the intraocular pressure from the sensor's measurement data.

[0049] It is defined that the excitation source connected to the device base via a positioning unit can be either the entire unit (from the actual excitation source to the nozzle) or just its nozzle, which, however, represents the location of the excitation source closest to the eye.

[0050] According to a first preferred embodiment, the central control unit has connections to the distance sensor and the positioning unit and is designed to maintain minimum distances to eye structures.

[0051] A first group of advantageous designs concerns the tonometric measuring unit itself. Preferably, tonometers based on air puff or shock wave technology are used.

[0052] This shows the Fig. 1. The construction of a first variant of the contactless tonometer.

[0053] The non-contact tonometer consists of an excitation source 2 and a sensor 3, both arranged on a device base 1, and a central control unit 7. The sensor 3 is rigidly connected to the device base 1, while the excitation source 2 is connected to the device base 1 via a positioning unit 8 and has a distance sensor 9 to maintain a minimum distance to the eye 6.

[0054] Here, the measuring axis 3' of the sensor 3 is approximately aligned with the corneal apex 6' of the eye 6 and the excitation axis 2' of the excitation source 2 is aligned with the sclera 6" of the eye 6.

[0055] The positioning unit 8 is designed to maintain a minimum distance from excitation source 2 and sensor 3 to eye 6 based on the signals from the distance sensor 9.

[0056] This is possible, for example, by designing the desired distance range of the sensor 3 from the corneal apex 6' to be fundamentally larger than the minimum distance of the excitation source 2 to the sclera 6" taking into account the range of variation of probable eye anatomies and the angle between 2' and 3'.

[0057] This allows the device base 1 to be manually positioned using the signals from the distance sensor 9 and, if applicable, the sensor 3 itself, so that the desired distance between sensor 3 and the corneal apex 6' is achieved. Subsequently, the excitation source 2 is positioned more precisely and automatically using the positioning unit 8 based on the signals from the distance sensor 9. In particular, the excitation source 2 is positioned at least with respect to its distance from the eye 6, but preferably also with respect to the direction of its excitation axis.

[0058] One advantage of this first variant is that the position of the stimulus source can be adjusted, for example, to avoid an anomaly of the ocular surface (scar, suture, wounds, implants, ulcers, scleral demarcation, etc.). This can be achieved through an automated comparison of the eye images captured by the camera with normative databases, possibly also with the aid of an automated evaluation using a trained rating system. During this positioning, a minimum distance can always be maintained via a distance sensor. Sensor 3, which can also be a camera, does not need to be moved and can remain further away.

[0059] A second group of advantageous embodiments relates to the arrangement of the sensors and excitation sources. In this arrangement, the excitation area of ​​the excitation source is directed towards a first structure of the eye, preferably the sclera, while the measuring area of ​​the sensor is directed towards a second structure of the eye, preferably the cornea and particularly preferably its apex.

[0060] Although the sclera is preferred as the excitation area of ​​the excitation source, it is possible that the excitation area may also be on the cornea.

[0061] A second variant of the design of the contactless tonometer shows the Fig. 2.

[0062] The contactless tonometer also consists of an excitation source 2 and a sensor 3, both of which are arranged on a device base 1, as well as a central control unit 7.

[0063] Unlike Fig. The device base 1 has a distance sensor 4 and its own positioning unit 5 to maintain a minimum distance to the eye 6. The sensor 3 is rigidly connected to the device base 1, while the excitation source 2 is connected to the device base 1 via its own positioning unit 8 and has another distance sensor 9 to maintain a minimum distance to the eye 6.

[0064] Here too, the measuring axis 3' of sensor 3 is aligned with the corneal apex 6' of eye 6 and the excitation axis 2' of excitation source 2 is aligned with the sclera 6" of eye 6.

[0065] The positioning units 5 and positioning unit 8 are designed to maintain different minimum distances from excitation source 2 and sensor 3 to eye 6 based on the signals from the two distance sensors 4 and 9.

[0066] Since both the excitation source 2 and the sensor 3 have distance sensors (9 and 4) and also their own positioning units 8 and 5 (sensor 3 via device base 1), in this case the smaller distance (in this case that of the excitation unit 2 via the positioning unit 5 of the device base 1) can first be set and then an optimization of the (larger) distance of the sensor 3 from the corneal apex 6' can be carried out, while the positioning unit 8 simultaneously keeps the optimal distance of the excitation source 2 from the sclera 6' as constant as possible, but in any case ensures the minimum distance by means of the distance sensor 9.

[0067] The positioning unit 5 of the device base offers the further advantage that camera images can also be used to reposition the sensor 3 in such a way as to avoid any anomalies in the detection area, for example on the cornea. Such corneal anomalies can be, for example, sutures, scars, wounds or opacities.

[0068] In a preferred embodiment, at least one further excitation source is provided, which is preferably arranged opposite the first excitation source and has an additional distance sensor. Particularly preferably, the at least one further excitation source is also connected to the device base via a positioning unit. This can be the same, shared positioning unit or a separate, additional positioning unit.

[0069] This shows the Fig. 3 the construction of a third variant of the contactless tonometer.

[0070] In this variant, the contactless tonometer has a sensor 3 and two excitation sources 2.1 and 2.2, which are arranged on the device base 1.

[0071] The device base 1 also has a distance sensor 4 and a positioning unit 5 to maintain the minimum distance to the eye 6 and a central control unit 7.

[0072] The excitation sources 2.1 and 2.2 are each connected to the device base 1 via a further positioning unit 8.1 and 8.2 and each have a further distance sensor 9.1 and 9.2.

[0073] Here too, the measuring axis 3' of sensor 3 is aligned with the corneal apex 6' of eye 6.

[0074] The excitation axis 2.1' of excitation source 2.1 is also aligned with the sclera 6" of eye 6. The excitation axis 2.2' of excitation source 2.2 is also aligned with the sclera 6", but with the opposite side of eye 6.

[0075] This variant also allows for different minimum distances between excitation sources 2.1 and 2.2 and sensor 3 and eye 6. Additionally, it is possible to set different minimum distances between excitation sources 2.1 and 2.2 and eye 6.

[0076] According to a preferred embodiment, the second variant of the contactless tonometer according to the invention can be simplified.

[0077] This shows the Fig. 4 the construction of a third variant of the contactless tonometer according to the invention.

[0078] In this variant, the contactless tonometer also has a sensor 3 and two excitation sources 2.1 and 2.2, which are arranged on the device base 1.

[0079] The device base 1 also has a distance sensor 4 and a positioning unit 5 to maintain the minimum distance to the eye 6 and a central control unit 7.

[0080] In contrast to the second variant, the two excitation sources 2.1 and 2.2 each have a distance sensor 9.1 and 9.2, but there is only one common positioning unit 8.3 which is connected to the device base 1.

[0081] Here too, the measuring axis 3' of sensor 3 is aligned with the corneal apex 6' of eye 6. The excitation axes 2.1' and 2.2' of the excitation sources 2.1 and 2.2 are aligned with the opposite sides of the sclera 6" of eye 6.

[0082] In this variant, too, it is possible to maintain different minimum distances between excitation sources 2.1 and 2.2 and sensor 3 and eye 6. Unlike the second variant, setting the same or different minimum distances between excitation sources 2.1 and 2.2 and eye 6 is achieved solely by rotating the positioning unit 8.3.

[0083] According to a third group of advantageous designs, the distance sensors utilize optical, capacitive, inductive, electromagnetic or ultrasonic operating principles.

[0084] Preferably, more than one distance sensor is rigidly connected to an excitation source or the device base, with the distance sensors preferably being based on at least two different operating principles.

[0085] Using more than one distance sensor can more reliably prevent unintentional contact of parts of the tonometer with the eye. This safety can be further enhanced by using distance sensors based on different operating principles, thus eliminating or compensating for potential problems associated with individual principles. For example, the generally individually varying backscatter of the eye tissue, such as that resulting from varying pigmentation or hydration, can cause errors in distance measurement using optically reflective distance sensors.

[0086] As experience shows, the distance to the eye is often very small, especially with various tonometers, so that contact with parts of the tonometer can occasionally occur, particularly in people with long eyelashes. However, unlike contact with the cornea or eyelid, this contact is generally not critical and should be treated accordingly.

[0087] The use of distance sensors based on different operating principles ensures that, for example, non-critical contact of parts of the tonometer with eyelashes is acceptable, while minimum distances to the sclera or cornea are still maintained. One possible approach is to arrange several optical distance sensors around the excitation source 2 in such a way that outlier values ​​caused by individual eyelashes only affect specific distance sensors, and these signals can be ignored when determining the minimum distance to the sclera and cornea.

[0088] It should also be mentioned that an OCT or OCDR system can be used as a sensor. This would have the advantage that, in addition to positions and distances, corneal curvatures could also be determined. Such systems, when using sufficiently high A-scan rates such as several tens of kHz, 100 kHz, or even MHz, also allow for the simultaneous detection of rapid eye movements and their correction via the positioning units.

[0089] Furthermore, OCT and OCDR can easily be designed so that the illumination and detection beams are collinear, allowing for space-saving configurations in the confined space in front of the patient's eye. In contrast, air-puff tonometers based on Scheimpflug cameras, such as the OCULUS CORVIS, always require a relatively large angle between the illumination and detection planes, which significantly increases the space required for these sensors.

[0090] According to another preferred embodiment, an additional distance sensor in the form of a camera is arranged at the base of the device to take frontal images of the eye, in particular the eyelid, iris, sclera, or eyelashes. This allows for the simple and unobtrusive detection of contact with eyelashes or eyelids.

[0091] A fourth group of advantageous embodiments relates to positioning units that are motorized and can be aligned manually or automatically. In particular, the positioning units are operated electromechanically, electromagnetically, piezoelectrically, hydraulically, pneumatically, electrothermally, or mechanically by springs.

[0092] An electrothermal operating principle includes, for example, actuators based on bi- or memory metals.

[0093] A spring-mechanical operating principle includes, for example, actuators that utilize a rapid retraction movement by means of a restoring movement through electromechanical release of a mechanical spring that was manually or motor-tensioned before the measurement.

[0094] In accordance with a preferred advanced training, the positioning units are designed to be configurable and controllable in various ways in order to achieve different minimum distances between different parts of the tonometer and eye structures.

[0095] According to further training, the positioning units can move the excitation units away from eye structures at more than 1 mm / s or, in particular, more than 10 mm / s.

[0096] According to a fifth group of advantageous designs, the positioning unit of the device base is designed to minimize the working distance of the excitation source to eye structures in a safe manner in order to reduce the necessary intensity of the excitation source on the eye.

[0097] In particular, the minimum distances between the tonometer and the eye are 0.5 mm to 5 mm or up to 20 mm. These minimum distances are determined by the distance between the stimulus source and ocular structures from the group consisting of the sclera, conjunctiva, cornea, limbus, and eyelid. According to a particularly favored advanced training method, a minimum distance to the eyelashes is not always maintained.

[0098] In accordance with a preferred advanced training, the positioning unit of the device base is designed to keep the minimum distance between the excitation source and the eye constant, even when the eye is moving.

[0099] The arrangement according to the invention provides a solution for contactless tonometric measurement of intraocular pressure.

[0100] In particular, the contactless tonometer features automated detection of distance and orientation to the eye, as well as automated positioning of the tonometer and its components. According to the invention, additional sensors are provided to prevent direct contact with the eye. Furthermore, excitation sources and sensors can be directed towards different parts of the eye and positioned independently of one another, which further minimizes the risk of eye contact.

[0101] The proposed non-contact tonometer enables consistent operation of the excitation and detection units, as the measurement signals generally depend both on the respective distance of the excitation and detection units from the eye and on each other. Furthermore, the ability to individually adjust the distance of the excitation and detection units can be used to increase measurement accuracy by, for example, varying the excitation and / or detection, thereby increasing the extracted information content. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] US 8.257.295 B2

[0003] DE 10 2018 107622 A1

[0012] US 9,462,947 B2

[0020] US 2016 / 0374554 A1 [0021, 0022] WO 2021 / 160924 A1 [0022, 0032] US 3,181,351 A

[0029] EP 1 402 810 B1

[0030] US 2020 / 0300236A1

[0031] Zitierte Nicht-Patentliteratur

[0000] F. Stapelton et al., „Corneal and conjunctival sensitivity to air stimuli“, Br J Ophthalmol 2004;88:1547-1551. doi: 10.1136 / bjo.2004.044024

[0015] Koprowski and Wilczyński, „Re-view Article Corneal Vibrations during Intraocular Pressure Measurement with an AirPuff Method“, Journal of Healthcare Engineering, Volume 2018, Article ID 5705749, https: / / doi.org / 10.1155 / 2018 / 5705749

[0019]

Claims

[1] Contactless tonometer, consisting of a device base, an excitation source movable relative to the device base, a sensor and a central control unit, characterized by that the excitation source is connected to the device base via a positioning unit and has a distance sensor rigidly connected to it, that the distance sensor and the positioning unit have connections and are designed to maintain minimum distances of the excitation source to eye structures and that the central control unit has connections to the excitation source and to the sensor and is designed to determine the intraocular pressure from the measurement data of the sensor. [2] Contactless tonometer according to claim 1, characterized by that the central control unit has connections to the distance sensor and the positioning unit and is designed to maintain minimum distances to eye structures. [3] Contactless tonometer according to claim 1, characterized bythat the tonometer is based on air-puff or shock wave technology. [4] Contactless tonometer according to claim 1, characterized by that the excitation area of ​​the excitation source is directed towards a first structure of the eye, preferably the sclera. [5] Contactless tonometer according to claim 4, characterized by that at least one further excitation source is present, which is preferably arranged opposite the first excitation source and has an additional distance sensor. [6] Contactless tonometer according to claim 5, characterized by that at least one further excitation source is also connected to the device base via a positioning unit. [7] Contactless tonometer according to claim 1, characterized by that the working distance of the excitation source to eye structures is minimized in a safe manner in order to reduce the necessary intensity of the excitation source on the eye. [8] Contactless tonometer according to claim 1, characterized by that the measuring range of the sensor is aligned to a second structure of the eye, preferably the cornea. [9] Contactless tonometer according to claim 1, characterized by that the minimum distance of the tonometer to the eye is 0.5mm, 1mm, 2mm, 5mm, 10mm or 20mm. [10] Contactless tonometer according to claim 1, characterized by that the minimum distance between an excitation source and eye structures from the group “sclera”, “conjunctiva”, “cornea”, “limbus”, “eyelid” is realized. [11] Contactless tonometer according to claim 1, characterized in that a minimum distance to eyelashes is not always maintained. [12] Contactless tonometer according to claim 6, characterized by that one, several or all positioning units are motorized and aligned manually or automatically. [13] Contactless tonometer according to claim 12, characterized bythat the positioning units operate electromotively, electromagnetically, piezoelectrically, hydraulically, pneumatically, electrothermally, spring-mechanically or similarly. [14] Contactless tonometer according to claim 13, characterized by that the positioning units can be configured and controlled in different ways in order to be able to realize different minimum distances to eye structures. [15] Contactless tonometer according to claim 1, characterized in that the positioning unit can move the excitation unit away from eye structures at more than 1 mm / s or more than 10 mm / s. [16] Contactless tonometer according to claim 9, characterized in that the positioning units are designed to realize the minimum distance by causing a withdrawal movement of the excitation source away from the eye when a threshold distance is undershot. [17] Contactless tonometer according to claim 9, characterized in that the positioning units are designed to realize a retraction movement when the threshold distance is undershot in less than 10 ms. [18] Contactless tonometer according to claims 15 and 16, characterized in that the positioning units are designed to realize a retraction movement of at least 1 mm within a maximum of 100 ms. [19] Contactless tonometer according to claims 16 to 18, characterized in that the positioning units are designed to realize a retraction movement by means of a return movement by electromechanical release of a mechanical spring tensioned manually or by motor before the measurement. [20] Contactless tonometer according to claim 1, characterized by that the distance sensors use optical, capacitive, inductive, electromagnetic or even ultrasonic-based operating principles. [21] Contactless tonometer according to claim 1, characterized in that more than one distance sensor is rigidly connected to an excitation source or the device base. [22] Contactless tonometer according to one of claims 20 or 21, characterized in that the distance sensors are based on at least two different operating principles. [23] Contactless tonometer according to claim 1, characterized by that an additional distance sensor in the form of a camera is arranged on the base of the device in order to take frontal images of the eye, in particular of the eyelid, the iris, the sclera or the eyelashes. [24] Contactless tonometer according to claim 23, characterized in that the positioning units are designed to position the excitation sources and / or the sensor using camera signals in such a way that the excitation and / or the detection does not occur on anomalies of the ocular surface.

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