WO2023152037A1 - Tonometer for measuring intraocular pressure - Google Patents

Abstract

The invention relates to a tonometer for measuring an intraocular pressure, wherein the examination is carried out without directly contacting the eye. The tonometer according to the invention for measuring intraocular pressure consists of a sound emitter, a surface deformation detector, a control unit, and means for damping noises produced during the measurement for the patient. The term "sound emitter" is to encompass all types of sound, shockwave, and air blast emitters which are suitable for contactlessly generating temporary surface deformations on the eye, said surface deformations being detectable by means of the surface deformation detector. The proposed tonometer is used to measure the intraocular pressure without contacting the eye and is provided in particular for home use. In principle, however, such tonometers are also suitable for clinical use.

Description

Tonometer for measuring intraocular pressure

The present invention relates to a tonometer for measuring the intraocular pressure, the examination being carried out without direct contact with the eye.

Glaucoma, also known as glaucoma, describes a series of eye diseases of different causes that result in irreversible damage to the nerve fibers of the optic nerve. As the disease progresses, this becomes noticeable at the exit point of the optic nerve as increasing hollowing (excavation) or pallor and atrophy of the optic nerve head (papilla). As a result, characteristic visual field defects (scotomas) develop, which in extreme cases can lead to blindness in the affected eye.

Elevated intraocular pressure (IOP) is one of the most important risk factors for glaucoma, which can also be easily measured on a regular basis. According to the prior art, different solutions are known for this. For the sake of completeness, it should be noted that the usually specified intraocular pressure (IOP) is the relative pressure of the interior of the eye, in particular of the aqueous humor, in relation to the atmospheric air pressure. If this relative pressure is significantly increased, for example, there is a noticeable hardening of the eye, which is why ophthalmologists carried out at least a qualitative assessment of the intraocular pressure by palpation before the availability of tonometers. However, absolute pressures must be distinguished from this IOP, such as are sometimes determined by intraocularly implanted pressure sensors if they are not related to the prevailing atmospheric air pressure (US Pat. No. 8,257,295 B2).

Applanation tonometry, which was developed by the Austrian-Swiss ophthalmologist Hans Goldmann, was a first, common and accurate method for determining the intraocular pressure. A small measuring body is attached to a special ophthalmological examination device, the slit lamp appropriate. During the examination, the force required to bring its planar front surface with a diameter of, for example, 3.06 mm (area=7.35 mm ² ) into contact with the cornea and flatten it is measured. The force used is generated by a spring balance coupled to a measuring drum. The pressure values can then be read directly from this because of the known contact surface. An aqueous solution of the dye fluorescein can also be dripped into the conjunctival sac beforehand for the examiner to visually check the contact between the cornea and the measuring body. There are also applanation tonometers that are hand-held to inspect, for example, people who are lying down.

Applanation tonometers have the major disadvantage that they are a contact method in which the sensitive cornea has to be touched directly. This generally requires anesthesia of the cornea. Furthermore, the measurement requires some time during which the patient is not allowed to move his eyes in order not to disturb the measurement or even cause corneal injuries. As with other corneal-based tonometry methods, the stiffness and viscoelasticity and in particular the thickness of the cornea can influence the pressure values determined. For people with a very thick cornea, the measurement result can be too high.

For a correction, it is therefore recommended, especially in the corresponding patient groups, to determine the corneal thickness before measuring the intraocular pressure. This is usually done with a so-called pachymeter. The correct value can then be determined using a conversion factor using a correction table.

An older method, also based on direct contact with the eye, is impression tonometry, for example using that developed by the Norwegian ophthalmologist Hjalmar August Schiotz tonometers. The device is placed by hand on the anesthetized cornea of the supine patient. It shows how deep a metal pin with a defined weight indents the cornea. The intraocular pressure can then be read from a calibrated table.

A problem with impression tonometry is that the instruments used are only calibrated for eyes with an average scleral distensibility and can give incorrect values for the intraocular pressure for myopic eyes.

A new procedure is the so-called Dynamic Contour Tonometry (DCT), whose dynamic measuring principle differs fundamentally from static applanation tonometry because it does not flatten the cornea, but the measuring head, which is modeled on the cornea, brings the cornea into its natural, tension-free state. The curvature of the cornea under the measuring head is only slightly reduced (flatter). The pressure between the measuring head and the cornea then corresponds to the intraocular pressure. A pressure sensor built into the head of the tonometer can record the eye pressure directly and largely independently of corneal influences. The precision achieved makes it possible to display pulse curves of the intraocular pressure, which are triggered by the heartbeat, similar to an ECG.

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

The Icare® id 00 from ICARE FINLAND OY is one of the so-called rebound tonometers. Its measuring principle is based on a moving, light probe that hits the eye and is decelerated and thrown back by it, with the deceleration and rebound behavior of the probe correlating with the intraocular pressure. This braking and rebound behavior is recorded inductively using a magnetized wire in the probe. the impact The speed of the probe is selected in such a way that the measurement can be carried out faster than the blinking reflex, i.e. it cannot be disturbed by patient reactions. Due to the light, rounded probe and the shortness of its impact, the measurement is hardly noticeable for the patient, so that a local anesthetic can usually be dispensed with. To increase the measurement accuracy, multiple measurements (e.g. 6) are usually carried out while the eyelid is open.

Furthermore, the method of tonography based on the above-mentioned tonometries still exists. In this case, the intraocular pressure is temporarily artificially increased and the change in volume and pressure reduction due to the outflow of aqueous humor are measured over a period of a few minutes and an outflow resistance is determined from this.

There are still methods of ophthalmodynamometry based on tonometry and artificial changes in intraocular pressure (DE10 2018 107622 A1), in which pulsation observations on retinal vessels depending on changes in intraocular pressure can be used to determine retinal blood pressure and the perfusion pressures derived therefrom, which are valuable for a complete glaucoma diagnosis.

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

At least direct contact with the cornea of the eye is avoided with transpalpebral scleral tonometry, since the measurement of the intraocular pressure is carried out through the eyelid. The tonometer also works according to the recoil principle, with a freely movable rod serving as a sensor by lowering it onto the eyelid in the area of the sclera. The sitting or lying patient, however, has to follow at a 45° angle look up. In this method, intraocular pressure measurement results are also dependent on the biomechanical condition of the lid and sclera, as well as the relative alignment of the eye 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 much 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). Although local anesthesia is not required when using this method, the patient still feels direct contact of the lid with the probe.

Airpuff Non-Contact Tonometry (Airpuff NCT) is a procedure in which there is no contact between the eye and the measuring instrument. The intraocular pressure is measured using an air pulse, which the cornea, depending on the intraocular pressure, does not do for a short time insignificantly, for example by 0.4 to 1 mm at time intervals of 10 to 30 ms. The measurement accuracy is usually somewhat lower compared to the contact measurement methods mentioned above. While impression and applanation tonometric examinations are exclusively ophthalmological activities, inspections and screening of the intraocular pressure using Airpuff-NCT are increasingly being used by opticians. From the patient's point of view, this measuring method is fundamentally attractive because of the freedom from contact and the fact that local anesthesia is not necessary, but in practice it is occasionally felt to be uncomfortable because of the unexpected, clearly noticeable puff of air.

The VISUPLAN® 500 from Carl Zeiss Meditec AG is a concrete example of Airpuff Non-Contact Tonometry. It is intuitive to use, with the touchscreen allowing you to choose between single and multiple measurements or a test air pulse and the measurement process then done automatically. The results are displayed directly on the monitor, but can also be transmitted or output via a serial interface. Another example of airpuff non-contact tonometry is the OCULUS CORVIS ST, in which, in addition to the tonometry, the biomechanical properties of the cornea are determined from their rebound behavior during surface deformation by the air blast, which is recorded using a high-speed camera with 4330 images/second . This is described in the literature (Koprowski and Wilczyhski, “Review Article Corneal Vibrations during Intraocular Pressure Measurement with an Air-Puff Method”, Journal of Healthcare Engineering, Volume 2018, Article ID 5705749, https://doi.org/10.1155/ 2018/5705749) that a series of surface vibrations can be detected that also have higher frequency components than the excitation air blast.

US Pat. No. 9,462,947 B2 in turn proposes a solution for contact-free measurement of the intraocular pressure using electromagnetic waves. For this purpose, laser radiation is directed onto the surface of the eye in order to generate vibrations or mechanical waves on the basis of photoacoustic phenomena. The surface vibrations thus generated are then detected using optical interferometry and/or optical coherence tomography and/or laser Doppler vibrometry in order to determine information regarding the intraocular pressure therefrom. It is also proposed to record additional measurement information, such as the curvature and/or thickness of the cornea and/or the water content of the eye, and to take this into account when determining the intraocular pressure.

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 in turn are detected contactlessly to obtain intraocular pressure information about the eye, for example also using the ultrasonic transducer mentioned in the document. The document WO 2021/160924 A1 in turn proposes an optical structure with an array of photodetectors Detection of eye surface movements for contactless intraocular pressure measurement. Emphasized advantages of exemplary embodiments in US 2016/0374554 A1 can be seen in the fact that no sensitive eye surfaces have to be touched and, in the case of a non-contact design, they can be used from one patient to another with a lower risk of contamination. In particular, spark gaps are proposed for generating non-linear sound waves for contact-free surface wave excitation.

However, the document also mentions that the use of such sound waves can have disadvantageous effects. For example, the sound waves generated by sparks can be audible, so the intensity of the emitted wave must even be controlled in such a way that there is no danger to hearing.

An associated unsolved problem of the tonometer described in US 2016/0374554 A1, but also of Airpuff tonometers, is that patients are irritated or frightened by the sound or air pressure wave generated for the measurement or even with several measurements, the time until spend the next sound emission under unpleasant tension.

The object of the present invention is therefore to develop a tonometer for measuring the intraocular pressure, in which the measurements are carried out without direct contact with the eye. In addition, the measurements should be able to be carried out by the patient himself and be as comfortable as possible for him, i. H. without the necessary use of mydriatics, anesthetics and without unacceptable mechanical or acoustic impairments.

This object is achieved with the tonometer for measuring the intraocular pressure, consisting of a sound generator, a surface deformation detector and a control unit, in that means are present to dampen the noises caused for the patient during the measurement (hereinafter also referred to as “measurement sound”). The term "sound generator" is intended to include all types of sound, shock wave and air blast generators that are suitable for generating temporary surface deformations on the eye without contact, which can be detected by the surface deformation detector.

According to the invention, the object is achieved by the features of the independent claims. Preferred developments and refinements are the subject matter of the dependent claims.

Advantageous configurations relate on the one hand to the generation of the sound waves and the detection of the surface deformations on the cornea, and in particular to means that are present to dampen the noise caused by the measurement for the patient. According to the invention, these are:

• a housing that contains the sound generator and the surface deformation detector and largely encloses the eye to be measured in a soundproof manner,

• Soundproofing devices that cover, enclose or even close the patient's ears,

• a noise generator that masks the noises caused by the measurement and

• Means for actively damping the noise caused by the measurement.

Accordingly, a first group of preferred developments relates to the housing whose contact surface on the patient's face is designed to be exchangeable or disinfectable. In addition, it is advantageous if the housing and/or its contact surfaces is/are designed to be soundproof. A second group of preferred developments relates to the noise protection devices that are worn on the head and are designed to be flexible or resilient. In particular, the soundproofing devices are designed as pure covers, as headphones or as earphones in order to passively dampen the noise caused by the measurement.

A third group of preferred developments relates to the noise generator, which is designed to generate noise or sound signals before the measurement in order to minimize the patient's perception of the noises generated during the measurement or to distract him.

A fourth group of preferred developments relates to means for active damping, in which the noise protection devices designed as headphones or earphones are connected to the control unit in order to forward the ambient noise picked up by a microphone to the control unit as far as possible, but actively transmit the noise caused during the measurement by means of to dampen anti-noise. In particular, the control unit is designed to use the sound transfer function determined for both ears to generate phase- and amplitude-adapted counter-sound curves with sufficiently broad sound spectra.

According to a fifth group of preferred developments, a combination of at least two means is used in the tonometer according to the invention in order to dampen the noise caused by the measurement for the patient.

According to a sixth preferred development, the tonometer for measuring the intraocular pressure also has a measuring device with which the patient's blood pressure can be measured promptly or simultaneously.

In particular, according to one embodiment, the housing is designed in such a way that two sound generators and two surface deformation detectors are present, so that both eyes to be measured are largely soundproof be enclosed and that additional noise protection devices are available. Particularly preferably, a microphone is additionally present for recording the noises caused during the measurement, the soundproofing devices are designed as headphones or earphones and the control unit is designed to actively dampen the noises caused by the measurements by counter-noise.

The proposed tonometer is used for measuring the intraocular pressure without eye contact and is intended in particular for home use. In principle, however, such tonometers are also suitable for clinical use.

The invention is described in more detail below using exemplary embodiments.

In addition, schematic diagrams show various configurations of the tonometer according to the invention. In particular, they show:

FIG. 1: a binocular head-mounted housing,

Figure 2: head-worn soundproofing devices that cover, enclose or close the patient's ears,

Figure 3: the functional principle of the noise generator,

Figure 4: the functional principle for active noise suppression using noise protection devices worn on the head,

Figure 5: the functional principle for active noise suppression by means of local counter-noise generation and FIG. 6: a particularly preferred embodiment of a housing worn on the head with soundproofing devices and active sound suppression.

The proposed tonometer for measuring the intraocular pressure consists of a sound generator to generate sound waves and direct them to the eye from a distance to trigger a surface wave on its ocular surface, e.g. cornea, a surface deformation detector to detect the surface wave on the ocular surface and a control unit for extracting wave information from the detected surface wave and determining the intraocular pressure of the eye. The sound waves are generated by the sound generator electromagnetically, optically, thermally or mechanically. The detector is based on optical interferometry and/or optical coherence tomography and/or laser Doppler vibrometry and/or the use of ultrasonic transducers and/or an eye surface movement detector based on an array of photodetectors.

Depending on the type of sounder, fast cameras (particularly Scheimpflug cameras >4000 Hz), laser triangulation sensors and chromatic confocal sensors are also suitable for surface deformation detection. In addition, there is also the possibility of detecting brief changes in the position of "landmarks" on or near the surface of the eye (such as blood or lymphatic vessels in the sclera or conjunctiva or nerves in the cornea) during the surface deformation of the eye induced by the transducer. For this purpose, however, the spatial resolution of the image recording must be adapted to the structure sizes of the "landmarks" (e.g. <10 pm for nerve cross-sections) and autofocusing on the structures must also be implemented.

According to the invention, the tonometer has means to dampen the noise caused by the measurement for the patient. In particular, these are: a housing that contains the sound generator and the surface deformation detector and largely encloses the eye to be measured in a soundproof manner,

• Soundproofing devices that cover, enclose or even close the patient's ears,

• a noise generator that masks the noises caused by the measurement and

• Means for actively damping the noise caused by the measurement.

The first group of preferred developments relates to the housing, which encloses the eye to be measured in a largely soundproof manner, with a contact surface between the housing and face of >5 cm ² , preferably >10 cm ² and particularly preferably >15 cm ² being selected. The contact surface should be dimensioned in such a way that the housing is as soundproof as possible and comfortable for the patient to wear. The housing is preferably designed binocularly and thus encloses both eyes to be measured in a largely soundproof manner.

This also has the advantage that, in addition to the patient, the environment (doctor, helpers, etc.) is little or not affected by the measurement sound.

In particular, the housing and/or its contact surface itself can be designed to be soundproof. In the case of the housing, this can be achieved, for example, by using a sound-absorbing material (plastic foam) and, in the case of the contact surfaces, by achieving a tight contact with the face without openings through which the sound can escape, for example with an elastic contact surface adapted to the face. For reasons of hygiene, the contact surfaces of the housing are designed to be replaceable or disinfectable. If the contact surface is designed to be interchangeable, non-woven paper or foam foil is preferably used. A contact surface that can be disinfected should be resistant to common disinfectants such as ethanol and isopropanol.

If the tonometer is attached to the face in an almost pressure-tight manner and the tonometer is pressed against the patient's face by means of a headband or air blasts are introduced to stimulate the surface deformation, there is a risk that overpressure could form in the tonometry system, which could falsify the measurement result. Therefore, either at least one sound-insulating pressure equalization opening is provided (e.g. as an open-pored plastic foam segment or slit) or an air pressure sensor inside the housing, with the help of which tonometry readings can be corrected in relation to the current air pressure surrounding the eyes. In order to detect an overpressure in the tonometer housing or, if necessary, to be able to adjust it by means of pumps (e.g. for the purpose of tonography or ophthalmodynamometry), another pressure sensor for the atmospheric air pressure outside the housing can also be used.

For this purpose, FIG. 1 shows the basic representation of a tonometer whose housing is designed binocularly and encloses both eyes to be measured in a largely soundproof manner. In principle, however, a monocular design is also possible, in which only one eye is enclosed at a time. However, if this monocular enclosure is to fit both eyes (right and left), then the enclosure must be made very adaptable and flexible, which reduces the overall stability and is therefore not preferred.

The tonometer according to the invention consists of two sound generators 1 and two surface deformation detectors 2, which are arranged in a housing 3, which is carried by means of a strap 4 on the head 5 of the patient and encloses both eyes 6 to be measured in a largely soundproof manner. The tonometer also has a control unit (not shown). The surface deformation detectors 2 must be positioned according to the necessity of the measurement principle used, for example on or near the line of sight for the use of OCT or at a sufficient angle thereto, for example for measurements using a Scheimpflug camera. The representation shown here to the side of the line of sight is therefore an example. Furthermore, the detection may require additional illumination of at least parts of the surface of the eye, for example using LEDs, SLDs or lasers (not shown).

According to an advantageous embodiment, the housing could also be designed as a patient-specific face mask according to US 2021/186319 A1.

The use of such a patient-specific face mask would have the advantage that a tight, i.e. comfortable and yet soundproof and possibly largely pressure-tight enclosure of the eye to be measured is guaranteed. In addition, a favorable alignment of the measurement system with respect to the individual patient's eye is achieved, which can minimize or even eliminate the effort involved in fine adjustment of the measurement system.

By being customized to the patient, the face mask can support self-administered ophthalmic procedures, particularly for home, portable, and/or personal use, for example.

When using a patient-specific face mask, the user can be confident that a predefined alignment is established between the ophthalmic system and a patient's eye, ensuring correct system-to-patient alignment. However, it may be necessary to take into account the patient's current viewing direction, ie, for example, changes in viewing direction due to the fixation light and/or Voice instructions are to be implemented or that the possibly varying viewing directions are to be captured by the camera and taken into account when the measurement is triggered (e.g. as in US Pat.

The face mask can be connected directly to an ophthalmic system for diagnosis. For example, perimeters, pachymeters, autorefractometers, ultrasound devices, slit lamps, tonometers or various ophthalmic imaging systems are conceivable as the ophthalmological system.

Such a patient-specific mask can be produced particularly cost-effectively using a 3D model of the patient's face as a 3D print, among other things.

Alternatively, such a face mask can also be designed in such a way that different sizes are available, the face contact surfaces of which are made soft and thick (1 ... 2 cm) in order to be able to use the face masks for various face shapes and sizes.

In particular, the sound transmitter and detector arranged in the housing can be designed to be adjustable with respect to the eye. In this case, the adjustment can be carried out by motorized displacements, preferably in several spatial directions. Camera signals from the eye (iris, pupil, limbus) and/or corneal reflections are used as adjustment feedback. Alternatively, OCT signals or laser triangulation sensors can also be used to position the measurement system in relation to the eye. As a further alternative, differently positioned, miniaturized measuring systems can be activated within the enclosures in order to achieve a positioning in relation to the eye that is sufficient for the fulfillment of the measuring task.

A second group of preferred developments relates to the soundproofing devices, which are purely covers, headphones or earphones are designed to passively dampen the noise caused by the measurement.

The noise protection devices are preferably worn on the head and are designed to be flexible or resilient. Alternatively, it can also be designed as a tabletop device, which the patient can rest their head on.

For this purpose, FIG. 2 shows three variants of noise protection devices worn on the head, which cover, enclose or close the ears of the patient.

The tonometer according to the invention consists of a sound generator 1 and a detector 2 and a control unit (not shown).

Depending on the configuration, the patient's ears 7 are covered, surrounded or closed by soundproofing devices 8 worn on the head 5 .

In particular, the soundproofing devices designed as headphones or earphones can also be used to transmit instructions to patients. For example, this may be instructed to follow the fixation light, rest your head against the device, or perform a Valsalva maneuver in which the nose is pinched to increase the pressure.

The Valsalva maneuver is a medical procedure and allows pressure peaks to be generated briefly in the eye in order to be able to carry out ophthalmodynamometric measurements to obtain additional information (https://de.wikipedia.org/wiki/Valsalva-Versuch#:~:text=3% 20See%20also-,version%C3%B,the%20respiratorymusculature%20and%20abdominalmusculature%20an). A third group of preferred developments relates to the noise generator, which is designed to generate and emit noise or sound signals, preferably before the measurement, in order to distract the patient from the noises caused by the measurement.

For example, a number of noises similar to the measurement noise can be emitted repeatedly (continuously) by the noise generator, so that a habituation effect occurs and the startle during the measurement decreases. It is further preferred that the masking noises from the noise generator, which are similar to the measurement noises, are only gradually increased in their amplitudes to the measurement noise level, in order to avoid the patient suddenly being startled during the actual measurement. A major advantage of noise masking is that there is hardly any patient reaction, such as the blinking reflex, to be expected during the actual measurement, so that several measurements can be carried out one after the other without the patient reacting specifically.

To transmit the masking noises generated by the noise generator, a loudspeaker is used, which can be located on the housing, the soundproofing devices, the noise generator or anywhere in the room.

In this embodiment variant, soundproofing devices in the form of headphones or earphones are preferably used in order to make the noise or sound signals generated by the sound generator available to the patient.

In this connection, it is particularly advantageous to couple the noise generator to the control unit of the tonometer, with the coupling being able to be wired or else wireless (by radio). This can ensure that the repeated (continuous) of the Noise or sound signals emitted by the noise generator are interrupted during the actual measurement of the intraocular pressure (and the noises thus caused by the measurement).

For this purpose, FIG. 3 shows the functional principle of the noise generator. The tonometer according to the invention consists of a sound generator 1, a surface deformation detector 2, carried on the patient's head 5 and enclosing the patient's ears 7 soundproofing devices 8 and a noise generator 9, which is connected to a control unit 11, which also controls the sound generator 1 and preferred also activates the surface deformation detector 2. The soundproofing device 8 not only insulates the ambient noise, but is also designed in such a way that the masking noise signals generated by the noise generator 9 are emitted into the patient's ear 7 by means of a loudspeaker 14 . For this purpose, the control unit 11 starts the noise generator 9, which preferably generates masking noises with increasing amplitude, until the control unit 11 then briefly deactivates the noise generator 9 and instead triggers the sound generator 1 and the measurement data acquisition via the surface deformation sensor 2. After the measurement, the noise generator 9 can be activated again to generate further masking noises before and after further measurements.

The diagram shown shows the progression over time (schematic noise intensities) of the noise signals. By gently ramping up masking noise amplitudes, startle at the first masking sound burst can be minimized. The noise signals generated by the noise generator are shown as gray bars and the noise signals caused by the measurement are shown as hatched bars.

A fourth group of preferred developments relates to means for active damping, in which the control unit is designed to actively dampen the noise caused by the measurement by means of anti-noise. Anti-noise is ideally 180° out of phase Sound signals that destructively interfere with the background noise at the location of the patient's ear.

A microphone 10 is preferably additionally present for this purpose, in order to record disturbing ambient and measurement noises and to forward them to the patient in a suitably amplified and phase-shifted manner as counter-noise.

Similar to the embodiment variant with the noise generator, soundproofing devices in the form of headphones or earphones are also preferably used here.

Alternatively, the control unit can also be designed for active damping of the noise caused by the measurement by means of counter-noise, using a microphone 10 attached in this case close to the measuring system and using test signals emitted by the headphones or earphones 14 that are acceptable for the patient, approximately the sound transfer functions determined by a sound generator 1 to the positions of the two patient ears 7. On the basis of the determined transfer functions, which are different due to the different distances between the ears 7 and the sound generator 2, the control unit can then generate optimally phase- and amplitude-matched counter-sound curves for both ears 7.

Dampening can be additionally improved in that the control unit is designed to actively dampen the sound waves emanating from the measurements with counter-noise, with a sufficiently broad sound spectrum of 20Hz to 20kHz, but at least 50Hz to 3kHz, having to be covered.

The generation of anti-noise is based on the detection of interference signals and the generation of phase-shifted, and thus destructively interfering, sound waves. Ideally, a phase shift of almost 180° is generated for all measurement sound components. This principle is known, for example, from Active Noise Cancellation (ANC) headphones. In the present case Frequency response and power output adapted to the parameters of the measurement sound and ensures that the interference signal detection takes place in a consistent and robust manner, in particular by a fixed position of the microphone 10 in relation to the main source of interference sounder 1 and the patient's ear 7.

Frequency responses can be further adapted to the reduced frequency responses of the ears of elderly patients, i.e. especially high frequencies above 15 or 10kHz or even 5kHz can probably be ignored. On the other hand, the occurrence of low frequencies can be very limited due to the shortness of the measurement sound used, i.e. it is usually sufficient if only frequencies above 50, 100, 200, 500 or even 1000Hz are processed.

For this purpose, FIG. 4 shows the basic illustration of noise protection devices worn on the head, which enclose the ears of the patient according to FIG. 3 and act on them with an opposing noise for active noise suppression.

Here, too, the tonometer according to the invention has a sound generator 1 and a surface deformation detector 2. The soundproofing devices 8 have headphones 14 and also microphones 10. The control unit 11 generates corresponding anti-sound curves from the measurement sound curves recorded by the microphones 8, to the headphones 14 transferred as part of the noise protection devices 8 and thus achieves an active measurement noise reduction.

In a preferred embodiment, the control unit is designed to determine the transfer functions to the two ears by means of a microphone 10, which is in this case attached close to a sound generator 1, and by means of test signals emitted by the headphones or earphones 14, and on the basis of these to determine the phase and amplitude-adapted counter-sound curves to create. This information can then be used to convert the measurement sound curves, which are also marked by means of the same microphone 10, into two phase- and amplitude-matched counter-sound curves on the two headphones 14.

Here, too, the surface deformation detector 2 is shown schematically (this time on the viewing axis), which can be implemented, for example, in the form of an OCT system that works collinear or almost collinear with the sound propagation direction. Transparent sound reflectors can be used for this.

In particular, the control unit of the measurement system can limit the generation of counter-noise to the direct measurement phase and thereby otherwise maintain or even enhance good perception, such as the conversation between patient and doctor. It can also be useful to retain a remainder of the measurement sound as a measurement indicator. Furthermore, it is conceivable that the measuring system limits the generation of counter-sound only to unpleasant measuring sound components, such as high frequency components.

However, active damping of the noise caused by the measurement is also possible through local counter-noise generation, for example through electronically delayed, additional noise sources in addition to the sound generator or possibly also through the emission of propagation-delayed components of the measurement noise, which themselves do not contribute to the measurement.

The anti-sound components could preferably even be generated by separate emitters at suitable distances from the measurement area and/or by appropriate shadowing using screens.

For this purpose, FIG. 5 shows the functional principle for active noise suppression by means of local counter-noise generation. The tonometer according to the invention consists of a sound generator 1 and a surface deformation detector 2. In addition, there is a further sound source 12 which transmits the measuring sound corresponding, but phase-shifted and amplitude-matched anti-sound (shown in the form of dashed sound waves) is generated.

The tonometer preferably has screens 13 which are intended to prevent the generated counter-noise from producing disruptive surface deformations on the eye, which are detected by the surface deformation detector 2 .

Based on the size of the room in which the measuring device is used, the sound and counter-noise sources would be positioned very close to each other (i.e. with only small angular distances for another person in the room), so that the sound signals emitted by the sound and counter-noise sources would be delayed with a suitable delay (ideally 180° phase shift for the main frequency components) can interfere sufficiently destructively in large parts of the room.

According to a fifth group of preferred developments, a combination of at least two means is used in the tonometer according to the invention in order to dampen the noise caused by the measurement for the patient.

In particular, the housing of a first embodiment is designed in such a way that two sound transmitters and two surface deformation detectors are present, that both eyes to be measured are largely enclosed in a soundproof manner and that further soundproofing devices are present.

According to a particularly preferred embodiment, there is also a microphone for recording the noises caused by the measurement, with the soundproofing devices being designed as headphones or earphones. Furthermore, the control unit is designed to actively dampen the noises caused by the measurements by counter-noise. For this purpose, FIG. 6 shows a particularly preferred embodiment of the tonometer according to the invention, consisting of a housing worn on the head with sound protection devices and active sound suppression.

The tonometer consists of two sound generators 1 and two surface deformation detectors 2, which are arranged in a housing 3, which is worn with the aid of a strap 4 on the patient's head 5 and encloses both eyes 6 to be measured in a largely soundproof manner.

In addition, the tonometer has soundproofing devices 8 which are arranged on the housing 3 or are worn on the patient's head 5 and enclose the patient's ears 7 . The noise protection devices 8 contain headphones 14 and also have microphones 10. The control unit 11 generates corresponding counter-sound profiles from the measurement sound profiles recorded by the microphones 8, transmits them to the headphones 14 in the noise protection devices 8 and thus actively reduces the measurement noise on the patient's ear 7 reached.

A sixth preferred development relates to a measuring device that is additionally present on the tonometer for measuring the intraocular pressure and with which the patient's blood pressure can be measured promptly or simultaneously.

As already mentioned, increased intraocular pressure (IOP) is one of the most important risk factors for glaucoma. It is also known that blood pressure values can be used in addition to IOP to estimate perfusion pressure.

Here, the IOP and blood pressure measurements should be carried out in a suitable order, for example to exclude or take into account that the blood pressure rises during the tonometry measurement as a result of the patient's excitement. In order not to disturb the blood pressure measurements by the tonometry, the measurements should be made in an appropriate order or in parallel but appropriately synchronized.

In the simplest case, the tonometer has a blood pressure measuring device in the form of an upper arm cuff with a pump, a release valve and a pressure and pulsation sensor.

In order to be able to measure the IOP for systolic and diastolic states or possibly also in between, the IOP measurement should be synchronized with the pulse/heartbeat, for example using the pulse curve determined in the blood pressure measurement.

For example, the ocular pulse amplitude (OPA) or a characteristic mean IOP can be determined, which would be more comparable with the values of a Goldmann tonometer (GAT).

With the arrangement according to the invention, a tonometer for measuring the intraocular pressure is made available, with which the measurement is carried out without direct contact with the eye.

In particular, the measurements are carried out without optical or acoustic impairments for the patient and are therefore very comfortable.

The proposed solution is based on a sound-based, ophthalmological measuring method in which a passive or active damping of disturbing measuring sound components takes place. A connection of the measurement system to the control unit of an active sound suppression is preferably used, for example to activate or control the sound suppression or to supply sound signals that are converted into counter-sound signals. The proposed tonometer is used for measuring the intraocular pressure without eye contact and is intended for clinical use. In principle, however, such tonometers are also suitable for home use.

Claims

patent claims 1 . Tonometer for measuring the intraocular pressure, consisting of a sound generator, a surface deformation detector and a control unit, characterized in that means are provided to dampen the noise caused by the measurement for the patient. 2. Arrangement according to claim 1, characterized in that the sound generator generates the sound waves electromagnetically, optically, thermally or mechanically. 3. Arrangement according to claim 1, characterized in that the surface deformation detector based on optical interferometry and / or optical coherence tomography and / or laser Doppler vibrometry and / or use of ultrasonic transducers and / or photodetector array based eye surface movement detector and / or fast laser triangulation and/or fast chromatic confocal sensors and/or fast camera-based near-surface imaging. 4. Tonometer according to claim 1, characterized in that the means is a housing which contains the sound generator and the surface deformation detector and largely encloses the eye to be measured in a soundproof manner. 5. Tonometer according to claim 1, characterized in that the means are noise protection devices that cover, enclose or also close the ears of the patient. 6. Tonometer according to claim 1, characterized in that the means is a noise generator which is designed to generate and emit noise or sound signals prior to the measurement. Tonometer according to claim 1, characterized in that the means for active damping of the noise caused by the measurement is designed. Tonometer according to Claim 4, characterized in that the housing is binocular. Tonometer according to Claim 8, characterized in that the housing is designed in such a way that its contact surface on the patient's face is > 5 cm ² , preferably > 10 cm ² and particularly preferably > 15 cm ² . Tonometer according to Claims 8 and 9, characterized in that the contact surface of the housing is designed to be exchangeable or disinfectable. Tonometer according to Claims 8 to 10, characterized in that the sound generators and surface deformation detectors arranged in the housing are designed to be adjustable in relation to the eyes. Tonometer according to Claims 8 to 11, characterized in that the housing and/or its contact surfaces is/are designed to be soundproof. Tonometer according to Claim 5, characterized in that the soundproofing devices are designed to be flexible or resilient. Tonometer according to claim 13, characterized in that the noise protection devices are worn on the head. Tonometer according to claim 13, characterized in that the soundproofing devices, as pure covers, as headphones or as Earphones are designed to passively dampen the noise caused by the measurement. Tonometer according to Claim 6, characterized in that the noise generator is designed to repeatedly emit a number of noises similar to the measurement noise. Tonometer according to Claim 7, characterized in that the control unit is designed to actively dampen the noises caused by the measurement by means of anti-noise. Tonometer according to Claim 17, characterized in that a microphone is additionally present in order to record ambient noise and transmit it to the patient. Tonometer according to Claims 17 and 18, characterized in that there are also noise protection devices in the form of headphones or earphones. Tonometer according to Claim 17, characterized in that the control unit is designed to actively dampen the sound waves emanating from the measurements by counter-sound, with a sufficiently broad sound spectrum of 20Hz to 20kHz, but at least 50Hz to 3kHz, being covered. Tonometer according to Claims 17 to 19, characterized in that the control unit is designed to determine the sound transfer function to the two ears by means of a microphone attached to the measuring system and by means of test signals emitted by the headphones or earphones. Tonometer according to claims 17 to 19, characterized in that the control unit is designed on the basis of the determined Sound transfer function to generate phase and amplitude-adapted anti-sound curves. Tonometer according to claims 4 to 7, characterized in that a combination of at least 2 agents is used. Tonometer according to Claim 21, characterized in that the housing is designed in such a way that two sound transmitters and two surface deformation detectors are present, that both eyes to be measured are largely enclosed in a soundproof manner and that sound protection devices are present. Tonometer according to Claim 22, characterized in that there is also a microphone for recording the noises caused by the measurement, that the noise protection devices are designed as headphones or earphones and that the control unit is designed to actively record the noises caused by the measurements to dampen anti-noise. Tonometer according to Claim 17, characterized in that the generation of counter-noise takes place essentially only during the measurements. Tonometer according to Claim 4, characterized in that a sensor for determining the air pressure surrounding the eyes is present in the housing. Tonometer according to claim 4, characterized in that the contact on the patient's face is designed so pressure-tight that an air pressure increase in the housing compared to the surrounding atmospheric air pressure can be achieved by means of a device for increasing the air pressure (pump). Tonometer according to Claim 28, characterized in that the tonometer has additional means in order to be able to carry out tonographic and/or ophthalmodynamometric measurements with it.