A system and a method for measuring pressure of an eye

Abstract

A system for measuring pressure of an eye comprises an excitation source (101) configured to produce an excitation and to direct the excitation via air towards the eye, a detector (102) for detecting an interaction between the excitation and a surface of the eye, and a processing system (103) for determining an estimate of the pressure of the eye based on the detected interaction between the excitation and the surface of the eye The excitation source comprises an ultrasonic source system emitting ultrasonic radiation and focusing the ultrasound radiation to the surface of the eye so that an area on the surface of the eye affected by an ultrasound radiation force is smaller than an area through which the ultrasonic radiation is emitted from the ultrasonic source system. Thus, ultrasound radiation force that is a nonlinear acoustic phenomenon is utilized.

Description

[0001] A system and a method for measuring pressure of an eye

[0002] Technical field

[0003] The invention relates to a system for measuring pressure of an eye of a human or an animal. Furthermore, the invention relates to a method for measuring pressure of an eye.

[0004] Background

[0005] Intraocular pressure “IOP” plays a major role in the pathogenesis of the open angle glaucoma, one of the leading causes of blindness. There are globally millions of people with the open angle glaucoma, about half of which are unknowingly affected and without diagnosis. The prevalence of open angle glaucoma increases with the aging of the human population, and it is expected that this will increase by 30% the number of open angle glaucoma cases during the next decade. A way to treat the open angle glaucoma is by lowering the intraocular pressure. An eye pressure measurement is a practical way of screening the open angle glaucoma. However, screening large parts of the population is needed to find undiagnosed cases. The other type of glaucoma is narrow angle glaucoma that causes a sudden eye pressure increase that may cause blindness in a few days. Since one permille of the population is affected with the acute narrow angle glaucoma, it would be advantageous to screen acute narrow angle glaucoma by measuring the eye pressure at health centers and other sites of the general health care as well as in the private health care sector. Therefore, it would be beneficial if every practitioner office had a system for measuring the eye pressure quickly and easily.

[0006] Contact methods such as e.g. Goldmann tonometry and Mackay-Marg tonometry for measuring eye pressure mostly require a local anesthetic to carry out the measurement and are thus impractical e.g. for screening large human populations. Non-contacting air impulse tonometers have been on the market for decades. A drawback of these tonometers is discomfort experienced by a human or animal whose eye pressure is being measured due to an air impulse directed towards andstriking the eye. The publication US6030343 describes a method that is based on an airborne ultrasonic beam that is reflected from a cornea. Excitation is done by a narrow band ultrasonic tone burst that deforms the cornea, and the phase shift of an ultrasonic tone burst reflected off the deformed cornea is measured to obtain an estimate of the eye pressure. Publications US2004193033 and US5251627 describe non-contact measurement methods based on acoustic and ultrasonic excitations. It is also possible to use a shock wave, i.e. a disturbance moving faster than the speed of sound, for excitation and to estimate eye pressure based on a response caused by the shock wave on a surface of an eye.

[0007] An inconvenience related to many of the above-described non-contact eye pressure measurement methods is that in practice it can be challenging to control with a sufficient accuracy a location on a surface of an eye to which the excitation is directed, and thus it may be challenging to carry out eye pressure measurements based on e.g. travelling speed of a surface wave caused by the excitation on the surface of the eye.

[0008] Summary

[0009] The following presents a simplified summary to provide basic understanding of some aspects of different invention embodiments. The summary is not an extensive overview of the invention. It is neither intended to identify key or critical elements of the invention nor to delineate the scope of the invention. The following summary merely presents some concepts of the invention in a simplified form as a prelude to a more detailed description of exemplifying and non-limiting embodiments of the invention.

[0010] In this document, the word “geometric” when used as a prefix means a geometric concept that is not necessarily a part of any physical object. The geometric concept can be for example a geometric point, a straight or curved geometric line, a geometric plane, a non-planar geometric surface, a geometric space, or any other geometric entity that is zero, one, two, or three dimensional, or four dimensional if the geometric concept changes with time and time is deemed to be the fourth dimension.In accordance with the invention, there is provided a new system for measuring the pressure of an eye. The measured pressure is typically the intraocular pressure “IOP” of the eye. A system according to the invention comprises:

[0011] - an excitation source configured to produce an excitation and to direct the excitation via air towards the eye,

[0012] - a detector for detecting an interaction between the excitation and the surface of the eye, and

[0013] - a processing system for determining an estimate of the pressure of the eye based on the detected interaction between the excitation and the surface of the eye.

[0014] The above-mentioned excitation source comprises an ultrasonic source system configured to emit ultrasonic radiation and to focus the ultrasound radiation to the surface of the eye so that an area on the surface of the eye affected by an ultrasound radiation force is smaller than an area through which the ultrasonic radiation is emitted from the ultrasonic source system.

[0015] The ultrasonic source system may comprise for example an array of ultrasonic sources configured to produce ultrasonic waves so that phase-differences between the ultrasonic waves are controllable, and the processing system can be configured to control the phase-differences to control an area on the surface of the eye affected by an ultrasound radiation force. The control of the area on the surface of the eye affected by the ultrasound radiation force may also comprise controlling the shape of the area. Thus, the location and / or the shape of the area on the surface of the eye affected by the ultrasound radiation force can be varied according to needs of an eye-pressure measurement process. For example, the ultrasound radiation force can be directed successively to two or more excitation areas distances apart from each other on the surface of the eye, and an estimate of e.g. travelling speed of a surface wave can be based on i) propagation times of the surface waves from the excitation areas to a detection area on the surface of the eye from which the surface waves are detected and ii) distances from the excitation areas to the detection area. The estimate of the travelling speed can be obtained e.g. by fitting a line to valuepairs each consisting of one of the propagation times and a respective one of the distances, wherein the slope of the line is indicative of the travelling speed.

[0016] For another example, the ultrasonic source system may comprise an array of ultrasonic sources such that the ultrasonic sources are mechanically directed to a same geometric point so that the ultrasound emitting surfaces of the ultrasonic sources coincide with a concave spherical geometric surface. In this exemplifying case, the focusing effect can be achieved also when the ultrasonic sources are driven by a common input signal and thus have a same phase, i.e. it not necessary to have ultrasound source -specific drive arrangements.

[0017] For a third example, the ultrasonic source system may comprise an ultrasonic source configured to generate an ultrasonic wave and an acoustic hologram plate on a route of the ultrasonic wave and having a two-dimensional pattern configured to focus the ultrasound radiation penetrating the acoustic hologram plate to the surface of the eye. More information about acoustic holograms can be found in e.g. Kai Melde et al., Holograms for acoustics, Nature, volume 537, pages 518-522, 2016.

[0018] The above-mentioned ultrasound radiation force is a nonlinear acoustic phenomenon that manifests itself as a nonzero force exerted by ultrasonic fields on the surface of the eye. More information about the acoustic force can be found in e.g. Palmeri, M. L. et al.: A Finite-Element Method Model of Soft Tissue Response to Impulsive Acoustic Radiation Force, IEEE Trans Ultrason Ferroelectr Freq Control. 2005 October; 52(10): 1699.

[0019] In accordance with the invention, there is also provided a new method for measuring the pressure of an eye. A method according to the invention comprises:

[0020] - producing an excitation and directing the excitation via air towards the eye,

[0021] - detecting an interaction between the excitation and the surface of the eye, and

[0022] determining an estimate of the pressure of the eye based on the detected interaction between the excitation and the surface of the eye.The excitation is produced with an ultrasonic source system emitting ultrasonic radiation and focusing the ultrasound radiation to the surface of the eye so that an area on the surface of the eye affected by an ultrasound radiation force is smaller than an area through which the ultrasonic radiation is emitted from the ultrasonic source system.

[0023] Various exemplifying and non-limiting embodiments are described in accompanied dependent claims.

[0024] Exemplifying and non-limiting embodiments both as to constructions and to methods of operation, together with additional objects and advantages thereof, are best understood from the following description of specific exemplifying embodiments when read in conjunction with the accompanying drawings.

[0025] The verbs “to comprise” and “to include” are used in this document as open limitations that neither exclude nor require the existence of un-recited features.

[0026] The features recited in dependent claims are mutually freely combinable unless otherwise explicitly stated.

[0027] Furthermore, it is to be understood that the use of “a” or “an”, i.e. a singular form, throughout this document does not exclude a plurality.

[0028] Brief description of figures

[0029] Exemplifying and non-limiting embodiments of the invention and their advantages are explained in greater detail below with reference to the accompanying drawings, in which:

[0030] Figure 1a illustrates a system according to an exemplifying and non-limiting embodiment for measuring pressure of an eye, and figures 1b and 1c illustrate functionalities of systems according to exemplifying and non-limiting embodiments,

[0031] Figure 2 illustrates a system according to an exemplifying and non-limiting embodiment for measuring pressure of an eye,Figure 3 shows exemplifying test results obtained with an array of ultrasonic sources and a laser Doppler vibrometer, and

[0032] Figure 4 shows a flowchart of a method according to an exemplifying and nonlimiting embodiment for measuring pressure of an eye.

[0033] Description of exemplifying and non-limiting embodiments

[0034] The specific examples provided in the description below should not be construed as limiting the scope and / or the applicability of the invention. Lists and groups of examples provided in the description below are not exhaustive unless otherwise explicitly stated.

[0035] Figure 1a illustrates a system according to an exemplifying and non-limiting embodiment for measuring pressure of an eye 110. The system comprises an excitation source 101 for producing an excitation and for directing the excitation via air towards the eye 110. The system comprises a detector 102 for detecting an interaction between the excitation and a surface of the eye 110. The system comprises a processing system 103 for determining an estimate of the pressure of the eye 110 based on the detected interaction between the excitation and the surface of the eye 110. The excitation source 101 comprises an ultrasonic source system configured to emit ultrasonic radiation and to focus the ultrasound radiation to the surface of the eye 110 so that an area on the surface of the eye affected by an ultrasound radiation force is smaller than an area through which the ultrasonic radiation is emitted from the ultrasonic source system. In this exemplifying case, the ultrasonic source system comprises an array of ultrasonic sources configured to produce ultrasonic waves such that phase-differences between the ultrasonic waves are controllable by the processing system 103 to control the area on the surface of the eye 110 affected by the ultrasound radiation force. The control of the area on the surface of the eye affected by the ultrasound radiation force may also comprise controlling the shape of the area. In figure 1a, three of the ultrasonic sources are denoted with references 104a, 104b, and 104c.

[0036] As shown in figure 1a, the ultrasonic sources are mechanically arranged so that main radiation beams of the ultrasonic sources are directed obliquely towards ageometric line 108 intersecting the array of ultrasonic sources perpendicularly at a geometric center point of the array of ultrasonic sources. In figure 1a, the main radiation beams of the ultrasonic sources 104a, 104b, and 104c are depicted with dashed line arrows 105a, 105b, and 105c, respectively. This mechanical arrangement facilitates focusing the ultrasonic resultant field formed by the ultrasonic waves produced by the ultrasonic sources.

[0037] In a system according to an exemplifying and non-limiting embodiment, the ultrasonic sources are directed to a same geometric point on the geometric line 108 so that the ultrasound emitting surfaces of the ultrasonic sources coincide with a concave spherical geometric surface. In this exemplifying case, the focusing effect can be achieved also when the ultrasonic sources are driven by a common input signal and thus have a same phase, i.e. it not necessary to have controllable phasedifferences between the ultrasonic sources.

[0038] In a system according to an exemplifying and non-limiting embodiment, the detector 102 comprises means for detecting a surface wave caused by the ultrasound radiation force directed to the surface of the eye 110. The surface wave can be e.g. a manifestation of a membrane wave, or another propagating disturbance, caused by the ultrasound radiation force directed to the cornea of the eye 100. The means for detecting the surface wave can be for example an optical interferometer, an optical coherence tomography device, a laser Doppler vibrometer “LDV” or another type of optical sensor for detecting motion of a surface e.g. such as described in FI129285B, or an ultrasonic transducer. The travelling speed of the surface wave on the surface of the eye 110 depends on the pressure of the eye 112. Therefore, in this exemplifying case, the processing system 103 can be configured to estimate the pressure of the eye based on the travelling speed of the detected surface wave.

[0039] Figure 1 b illustrates functionality of a system according to an exemplifying and nonlimiting embodiment where the processing system 103 is configured to control the array of the ultrasonic sources to direct the ultrasound radiation force successively to excitation areas 106a, 106b, and 106b distances apart from each other on the surface of the eye 110. The focal point or points of the ultrasonic radiation can be shifted between the excitation areas quickly by controlling the phase differencesbetween the ultrasonic sources. Correspondingly, the shape or shapes of the focal point or points can be varied quickly by controlling the phase differences between the ultrasonic sources. The processing system 103 is configured to estimate the travelling speed of the surface wave based on i) propagation times of the surface waves from the excitation areas to a detection area 107 on the surface of the eye from which the surface waves are detected and ii) distances d1 , d2, and d3 from the excitation areas to the detection area. To estimate the travelling speed, the processing system 103 can be, for example, configured to fit a line to value pairs each consisting of one of the propagation times and a respective one of the distances, where the slope of the line is indicative of the travelling speed of the surface waves from the excitation areas to the detection area. The use of many excitation areas and the line fitting provides more accuracy and reliability in the estimation of the travelling speed compared to a case in which only one excitation area is used. The line fitting can be based on e.g. the least mean square “LMS” optimization.

[0040] In a system according to an exemplifying and non-limiting embodiment, the detector 102 comprises means for detecting a displacement of the surface of the eye 110 caused by the ultrasound radiation force directed to the surface of the eye 110. The means for detecting the displacement can be for example an optical interferometer, an optical coherence tomography device, a laser Doppler vibrometer or another type of optical sensor for detecting motion of a surface e.g. such as described in FI129285B, or an ultrasonic transducer. The oscillation rate of the displacement in the direction perpendicular to the surface of the eye 110 depends on the pressure of the eye 110. Correspondingly, the shape of the waveform of the displacement as a function of time may depend on the pressure of the eye 110. Therefore, in this exemplifying case, the processing system 103 can be configured to estimate the pressure of the eye 110 based on the oscillation rate of the detected displacement and / or on the shape of the waveform of the displacement as a function of time. For another example, the speed at which the surface of the eye indents when being pushed by the ultrasound radiation force depends on the pressure of the eye. Therefore, the processing system 103 can be configured to estimate the pressure of the eye based on the indention speed of the surface of the eye. For a thirdexample, a speed at which the indented surface of the eye returns towards its normal position depends on the pressure of the eye. Therefore, the processing system 103 can be configured to estimate the pressure of the eye based on the speed at which the indented surface of the eye returns towards its normal position after being pushed by the ultrasound radiation force. For a fourth example, a delay after which the indented surface of the eye returns towards its normal position depends on the pressure of the eye. Therefore, the processing system 103 can be configured to estimate the pressure of the eye based on the delay after which the indented surface of the eye returns towards its normal position after being pushed by the ultrasound radiation force. For a fifth example, a indentation depth of the surface of the eye when being pushed by the ultrasound radiation force depends on the pressure of the eye. Therefore, the processing system 103 can be configured to estimate the pressure of the eye based on the indentation depth.

[0041] The estimation accuracy of the above-described embodiments based on detecting the displacement of the surface of the eye 110 can be improved by directing the excitation successively to two or more excitation areas distances apart from each other on the surface of the eye 110 in the way as shown figure 1 b. Preliminary eyepressure estimate values can be obtained based on detecting the displacement of the surface of the eye 110 corresponding to the excitation areas, and the final eyepressure estimate can be formed as a mathematical function, e.g. an arithmetic average, of the preliminary eye-pressure estimate values.

[0042] Figure 1c illustrates functionality of a system according to an exemplifying and nonlimiting embodiment where the processing system 103 is configured to control the array of ultrasonic sources to direct the ultrasound radiation force to an elongated area 106 forming an arc on the surface of the eye 110, and the detector 102 is configured to detect the displacement of the surface of the eye on a detection area 107 towards which the arc opens. The arc-shaped form of the area 106 excited by the ultrasound radiation force focuses the mechanical disturbance caused by the ultrasound radiation force to the detection area 107 and thus improves the accuracy and reliability of the eye-pressure measurement.Figure 2 illustrates a system according to an exemplifying and non-limiting embodiment for measuring pressure of an eye 210. The system comprises an excitation source 201 for producing an excitation and for directing the excitation via air towards the eye 210. The system comprises a detector 202 for detecting an interaction between the excitation and a surface of the eye 210. The system comprises a processing system 203 for determining an estimate of the pressure of the eye 210 based on the detected interaction between the excitation and the surface of the eye 210. The excitation source 201 comprises an ultrasonic source system configured to emit ultrasonic radiation and to focus the ultrasound radiation to the surface of the eye 210 so that an area on the surface of the eye affected by an ultrasound radiation force is smaller than an area through which the ultrasonic radiation is emitted from the ultrasonic source system. In this exemplifying case, the ultrasonic source system comprises an ultrasonic source 214 configured to generate an ultrasonic wave and an acoustic hologram plate 215 on the route of the ultrasonic wave and having a two-dimensional pattern configured to focus the ultrasound radiation penetrating the acoustic hologram plate to the surface of the eye 210.

[0043] It is to be noted that the above-presented technical solutions are non-limiting examples only, and other technical solutions for producing an estimate of the eye pressure based on the interaction between the ultrasound radiation force and the surface of the eye are also possible. Furthermore, in exemplifying and non-limiting embodiments, two or more different technical solutions are used to produce two or more estimates of the eye pressure to improve the reliability and the accuracy of the pressure measurement. The final estimate of the eye pressure can be derived with e.g. a predetermined mathematical rule based on two or more estimates obtained with two or more different technical solutions. The final estimate can be e.g. an arithmetic average of the two or more estimates obtained with the two or more technical solutions.

[0044] The processing system 103 shown in figure 1a as well as the processing system 203 shown in figure 2 can be implemented with one or more processor circuits, each of which can be a programmable processor circuit provided with appropriate software, a dedicated hardware processor such as for example an application specific integrated circuit “ASIC”, or a configurable hardware processor such as forexample a field programmable gate array “FPGA”. The software may comprise e.g. firmware that is a specific class of computer software that provides low-level control for hardware of the processing system 103 and / or the processing system 203. The firmware can be e.g. open-source software. Furthermore, the processing system 103 and / or the processing system 203 may comprise one or more memory circuits each of which can be for example a random-access-memory “RAM” circuit.

[0045] Figure 3 shows exemplifying test results obtained with an array of 35 kHz ultrasonic sources and a laser Doppler vibrometer. An eye under test is an eye of a dead pig that is artificially arranged to have a known eye-pressure. The array of 35 kHz ultrasonic sources produces the ultrasound excitation on the time-period from zero to 0.25 ms. Thereafter, the surface of the eye oscillates freely, i.e. without excitation. The curves shown in figure 3 are measured with the laser Doppler vibrometer and they indicate the displacement of a point on the surface of the eye in a direction substantially perpendicular to the surface of the eye. Figure 3 shows the curves corresponding to eye-pressures 5, 10, 15, 20, 30, 40, 60, and 60 mmHg. For example, curve 321 corresponds to the eye-pressure 5 mmHg and curve 322 corresponds to the eye-pressure 60 mmHg. As shown by the curves in figure 3, the eye-pressure has clear effects on the oscillation amplitude and the oscillation frequency after the excitation period.

[0046] Figure 4 shows a flowchart of a method according to an exemplifying and nonlimiting embodiment for measuring pressure of an eye. The method comprises the following actions:

[0047] - action 401 : producing an excitation with an ultrasonic source system emitting ultrasonic radiation and focusing the ultrasound radiation to the surface of the eye so that an area on the surface of the eye affected by an ultrasound radiation force is smaller than an area through which the ultrasonic radiation is emitted from the ultrasonic source system,

[0048] action 402: detecting an interaction between the excitation and the surface of the eye, andaction 403: determining an estimate of the pressure of the eye based on the detected interaction between the excitation and the surface of the eye.

[0049] In a method according to an exemplifying and non-limiting embodiment, the ultrasonic source system comprises an array of ultrasonic sources configured to produce ultrasonic waves interacting with each other so that the ultrasound radiation is focused to the surface of the eye.

[0050] In a method according to an exemplifying and non-limiting embodiment, the ultrasonic sources are phase-controllable so that phase-differences between the ultrasonic waves are controllable, and the method comprises controlling the phasedifferences to control the area on the surface of the eye affected by the ultrasound radiation force.

[0051] In a method according to an exemplifying and non-limiting embodiment, the ultrasonic sources are mechanically arranged so that main radiation beams of the ultrasonic sources are directed obliquely towards a geometric line intersecting the array of ultrasonic sources perpendicularly at a geometric center point of the array of ultrasonic sources. The ultrasonic sources can be directed, for example, to a same geometric point on the geometric line so that the ultrasound emitting surfaces of the ultrasonic sources coincide with a concave spherical geometric surface.

[0052] In a method according to an exemplifying and non-limiting embodiment, the ultrasonic source system comprises an ultrasonic source configured to generate an ultrasonic wave and an acoustic hologram plate on the route of the ultrasonic wave and having a two-dimensional pattern configured to focus the ultrasound radiation penetrating the acoustic hologram plate to the surface of the eye.

[0053] In a method according to an exemplifying and non-limiting embodiment, the interaction between the excitation and the surface of the eye is detected by detecting a surface wave caused by the ultrasound radiation force directed to the surface of the eye. The surface wave can be detected with an optical interferometer, an optical coherence tomography device, a laser Doppler vibrometer or another type of optical sensor for detecting motion of a surface e.g. such as described in FI129285B, and / or an ultrasonic transducer.A method according to an exemplifying and non-limiting embodiment comprises determining the estimate of the pressure of the eye based on travelling speed of the surface wave on the surface of the eye and caused by the ultrasound radiation force directed to the surface of the eye.

[0054] In a method according to an exemplifying and non-limiting embodiment, the ultrasonic source system comprises an array of phase-controllable ultrasonic sources, and the method comprises:

[0055] - controlling the array of ultrasonic sources to direct the ultrasound radiation force successively to two or more excitation areas distances apart from each other on the surface of the eye, and

[0056] - estimating the travelling speed of the surface wave based on i) propagation times of the surface waves from the excitation areas to a detection area on the surface of the eye from which the surface waves are detected and ii) distances from the excitation areas to the detection area.

[0057] The above-mentioned travelling speed can be estimated, for example, by fitting a line to value pairs each consisting of one of the propagation times and a respective one of the distances, where the slope of the line is indicative of the travelling speed of the surface waves from the excitation areas to the detection area.

[0058] In a method according to an exemplifying and non-limiting embodiment, the interaction between the excitation and the surface of the eye is detected by detecting a displacement of the surface of the eye caused by the ultrasound radiation force directed to the surface of the eye, and the estimate of the pressure of the eye is determined based on behavior of the displacement of the surface of the eye. The displacement can be detected with an optical interferometer, an optical coherence tomography device, a laser Doppler vibrometer or another type of optical sensor for detecting motion of a surface e.g. such as described in FI129285B, and / or an ultrasonic transducer.

[0059] A method according to an exemplifying and non-limiting embodiment comprises detecting the displacement of the surface of the eye and determining the estimateof the pressure of the eye based on an oscillation rate of the displacement of the surface of the eye and / or on the shape of the waveform of the displacement as a function of time. In a method according to an exemplifying and non-limiting embodiment, the estimate of the pressure of the eye is determined based on a speed at which the surface of the eye indents when being pushed by the ultrasound radiation force. In a method according to an exemplifying and non-limiting embodiment, the estimate of the pressure of the eye is determined based on a speed at which the indented surface of the eye moves back towards its normal position after being pushed by the ultrasound radiation force. In a method according to an exemplifying and non-limiting embodiment, the estimate of the pressure of the eye is determined based on a delay after which the indented surface of the eye moves back towards its normal position after being pushed by the ultrasound radiation force. In a method according to an exemplifying and non-limiting embodiment, the estimate of the pressure of the eye is determined based on a indentation depth of the surface of the eye when being pushed by the ultrasound radiation force.

[0060] In a method according to an exemplifying and non-limiting embodiment, the ultrasonic source system comprises an array of phase-controllable ultrasonic sources, and the method comprises:

[0061] - controlling the array of ultrasonic sources to direct the ultrasound radiation force successively to two or more excitation areas distances apart from each other on the surface of the eye,

[0062] - forming preliminary estimate values of the pressure of the eye based on the displacement of the surface of the eye corresponding to situations in which the ultrasound radiation force is directed successively to the two or more excitation areas, and

[0063] forming the estimate of the of the pressure of the eye as a mathematical function, e.g. as an arithmetic average, of the preliminary estimate values of the pressure of the eye.In a method according to an exemplifying and non-limiting embodiment, the ultrasonic source system comprises an array of phase-controllable ultrasonic sources, and the method comprises controlling the array of ultrasonic sources to direct the ultrasound radiation force to an elongated excitation area forming an arc on the surface of the eye, and detecting the displacement of the surface of the eye from a detection area towards which the arc opens.

[0064] The non-limiting, specific examples provided in the description given above should not be construed as limiting the scope and / or the applicability of the invention. Furthermore, any list or group of examples presented in this document is not exhaustive unless otherwise explicitly stated.

Claims

What is claimed is:

1. A system for measuring pressure of an eye, the system comprising:- an excitation source (101, 201) configured to produce an excitation and to direct the excitation via air towards the eye,- a detector (102, 202) for detecting an interaction between the excitation and a surface of the eye, and- a processing system (103, 203) for determining an estimate of the pressure of the eye based on the detected interaction between the excitation and the surface of the eye,characterized in that the excitation source comprises an ultrasonic source system configured to emit ultrasonic radiation and to focus the ultrasound radiation to the surface of the eye so that an area on the surface of the eye affected by an ultrasound radiation force is smaller than an area through which the ultrasonic radiation is emitted from the ultrasonic source system.

2. A system according to claim 1, wherein the ultrasonic source system comprises an array of ultrasonic sources (104a-104c) configured to produce ultrasonic waves interacting with each other so that the ultrasound radiation is focused to the surface of the eye.

3. A system according to claim 2, wherein the ultrasonic sources are phase-controllable so that phase-differences between the ultrasonic waves are controllable, and the processing system is configured to control the phasedifferences to control the area on the surface of the eye affected by the ultrasound radiation force.

4. A system according to claim 2 or 3, wherein the ultrasonic sources are mechanically arranged so that main radiation beams (105a-105c) of the ultrasonic sources are directed obliquely towards a geometric line (108) intersecting the array of ultrasonic sources perpendicularly at a geometric center point of the array of ultrasonic sources.

5. A system according to claim 4, wherein the ultrasonic sources are directed to a same geometric point on the geometric line (108) so that the ultrasound emitting surfaces of the ultrasonic sources coincide with a concave spherical geometric surface.

6. A system according to claim 1, wherein the ultrasonic source system comprises an ultrasonic source (214) configured to generate an ultrasonic wave and an acoustic hologram plate (215) on a route of the ultrasonic wave and having a two-dimensional pattern configured to focus the ultrasound radiation penetrating the acoustic hologram plate to the surface of the eye.

7. A system according to any one of claims 1-6, wherein the detector (102) is configured to detect a surface wave caused by the ultrasound radiation force directed to the surface of the eye, and the processing system (103) is configured to determine the estimate of the pressure of the eye based on travelling speed of the surface wave on the surface of the eye.

8. A system according to claim 3, wherein the detector (102) is configured to detect a surface wave caused by the ultrasound radiation force directed to the surface of the eye, and the processing system is configured to:- control the array of ultrasonic sources to direct the ultrasound radiation force successively to two or more excitation areas (106a-106b) distances apart from each other on the surface of the eye,- estimate travelling speed of the surface wave based on i) propagation times of surface waves from the excitation areas to a detection area (107) on the surface of the eye from which the surface waves are detected and ii) distances (d1-d3) from the excitation areas to the detection area, and- determine the estimate of the pressure of the eye based on travelling speed of the surface wave on the surface of the eye.

9. A system according to claim 8, wherein the processing system is configured to fit a line to value pairs each consisting of i) one of the propagation times and ii) arespective one of the distances, a slope of the line being indicative of the travelling speed of the surface waves from the excitation areas to the detection area.

10. A system according to any one of claims 1-9, wherein the detector (102) is configured to detect a displacement of the surface of the eye caused by the ultrasound radiation force directed to the surface of the eye, and the processing system (103) is configured to determine the estimate of the pressure of the eye based on behavior of the displacement of the surface of the eye.

11. A system according to claim 10, wherein the processing system (103) is configured to determine the estimate of the pressure of the eye based on oscillation rate of the displacement of the surface of the eye.

12. A system according to claim 3, wherein the detector (102) is configured to detect a displacement of the surface of the eye caused by the ultrasound radiation force directed to the surface of the eye, and the processing system is configured to:- control the array of ultrasonic sources to direct the ultrasound radiation force successively to two or more excitation areas (106a-106b) distances apart from each other on the surface of the eye,- form preliminary estimate values of the pressure of the eye based on the displacement of the surface of the eye corresponding to situations in which the ultrasound radiation force is directed successively to the two or more excitation areas, and- form the estimate of the of the pressure of the eye as a mathematical function of the preliminary estimate values of the pressure of the eye.

13. A system according to any one of claims 1 -6, wherein:- the ultrasonic source system is configured to direct the ultrasound radiation force to an elongated area (106) forming an arc on the surface of the eye,- the detector is configured to detect a displacement of the surface of the eye from a detection area (107) towards which the arc opens, and- the processing system (103) is configured to determine the estimate of the pressure of the eye based on behavior of the displacement of the surface of the eye.

14. A system according to any one of claims 1-13, wherein the detector (102) comprises one of following: an optical interferometer, an optical coherence tomography device, a laser Doppler vibrometer, and an ultrasonic transducer.

15. A method for measuring pressure of an eye, the method comprising:- producing (401 ) an excitation and directing the excitation via air towards the eye,- detecting (402) an interaction between the excitation and a surface of the eye, and- determining (403) an estimate of the pressure of the eye based on the detected interaction between the excitation and the surface of the eye,characterized in that the excitation is produced (401) with an ultrasonic source system emitting ultrasonic radiation and focusing the ultrasound radiation to the surface of the eye so that an area on the surface of the eye affected by an ultrasound radiation force is smaller than an area through which the ultrasonic radiation is emitted from the ultrasonic source system.

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