A tonometer for measuring intraocular pressure of an eye using an air pulse having a cut off edge

Abstract

Disclosed is a tonometer (100) for measuring intraocular pressure of an eye (150), the tonometer comprising: an air pulse generator (102); a corneal oscillation measurement sensor (104), and a controller (106) communicably coupled to air pulse generator and corneal oscillation measurement sensor, wherein the controller is configured to: control the air pulse generator to provide an excitation air pulse (108) towards a cornea (152) of the eye during a first time period (T1), wherein provided excitation air pulse has a first intensity (I) at an end time (T1e) of first time period, and this intensity is reduced from first intensity to a second intensity during a second time period (T2), wherein the second time period is after first time period, for producing corneal oscillations (320, 330); measure a signal related to corneal oscillations, using corneal oscillation measurement sensor; and determine intraocular pressure from measured signal.

Description

[0001] A TONOMETER. FOR MEASURING INTRAOCULAR PRESSURE OF AN EYE USING AN AIR PULSE HAVING A CUT OFF EDGE

[0002] TECHNICAL FIELD

[0003] The present disclosure relates to tonometers. Moreover, the present disclosure also relates to methods for measuring intraocular pressure of eyes with tonometers.

[0004] BACKGROUND

[0005] The accurate measurement of intraocular pressure (IOP) is essential in ophthalmic diagnostics. It serves as a fundamental parameter for assessing ocular health and detecting abnormalities, particularly in detecting conditions such as glaucoma which causes damage to optic nerve leading to progressive vision impairment. A tonometer is an instrument used for measuring IOP. The tonometer may be a rebound (or impact) tonometer, a dynamic contour tonometer, a non-contact tonometer, a Goldmann applanation tonometer (GAT), or similar.

[0006] Problem with contact tonometer is risk of infection and discomfort. One non-contact tonometer type is air puff tonometer in which a flow of air is provided towards eye surface to deform the surface to applanation point. The force of the flow of air in which the applanation point is reached is a function of intra ocular pressure of the eye. Problem with this approach is that it requires relatively large forces causing discomfort.

[0007] Therefore, in light of the foregoing discussion, there exists a need to overcome the aforementioned drawbacks.

[0008] SUMMARY

[0009] The aim of the present disclosure is to provide a tonometer and a method for measuring intraocular pressure of an eye with a tonometer, which produce high-amplitude corneal oscillations that enable accurate determination of the intraocular pressure. The aim of the present disclosure is achieved by a tonometer and method for measuring intraocular pressure of an eye with a tonometer, as defined in the appended independent claims to which reference is made to. Advantageous features are set out in the appended dependent claims.

[0010] Throughout the description and claims of this specification, the words "comprise" , "include", "have", and "contain" and variations of these words, for example "comprising" and "comprises" , mean "including but not limited to", and do not exclude other components, items, integers or steps not explicitly disclosed also to be present. Moreover, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

[0011] BRIEF DESCRIPTION OF THE DRAWINGS

[0012] FIG. 1 is an illustration of a schematic representation of a tonometer used for measuring intraocular pressure of an eye, in accordance with an embodiment of the present disclosure;

[0013] FIG. 2 is an illustration of a schematic representation of an air pulse generator of the tonometer of FIG. 1, in accordance with an embodiment of the present disclosure;

[0014] FIG. 3 is an illustration of a first graphical representation of a variation of an intensity of excitation air pulse at a cornea of an eye with respect to time, and a second graphical representation of a variation of a displacement of an apex of the cornea with respect to time, in accordance with an embodiment of the present disclosure; FIG. 4 is an illustration of a graphical representation of intraocular pressure as a function of corneal frequency, in accordance with an embodiment of the present disclosure; and

[0015] FIG. 5 is an illustration of a flowchart depicting steps of a method for measuring intraocular pressure of an eye with a tonometer, in accordance with an embodiment of the present disclosure.

[0016] DETAILED DESCRIPTION OF EMBODIMENTS

[0017] The following detailed description illustrates embodiments of the present disclosure and ways in which they can be implemented. Although some modes of carrying out the present disclosure have been disclosed, those skilled in the art would recognize that other embodiments for carrying out or practising the present disclosure are also possible.

[0018] In a first aspect, the present disclosure provides a tonometer for measuring intraocular pressure of an eye, the tonometer comprising: an air pulse generator, a corneal oscillation measurement sensor, and a controller communicably coupled to the air pulse generator and the corneal oscillation measurement sensor, wherein the controller is configured to: control, when in use, the air pulse generator to provide an excitation air pulse towards a cornea of the eye during a first time period, wherein the provided excitation air pulse has a first intensity at an end time of the first time period, and this intensity is reduced from the first intensity to a second intensity during a second time period, wherein the second time period is after the first time period, for producing corneal oscillations; measure a signal related to the corneal oscillations, using the corneal oscillation measurement sensor; and determine the intraocular pressure from the measured signal. The present disclosure provides the aforementioned tonometer, which enables production of strong corneal oscillations. The air pulse generator is effectively controlled to rapidly reduce the intensity of the provided excitation air pulse during the second time period, and as a result of such rapid intensity reduction, the cornea oscillates strongly. This rapid reduction of the intensity of the provided excitation air pulse is because the air pulse generator quickly removes the excitation air pulse during the second time period. Beneficially, the quick removal of the excitation air pulse generates high peak amplitudes of the corneal oscillations, since the cornea responds to said removal by quickly moving from its pressure- displaced position (due to the first intensity) towards its normal position. The signal related to such strong corneal oscillations is accurately measurable and allows to determine intraocular pressure (IOP). The signal related to strong corneal oscillations distinctly represents even the smallest of changes in corneal displacement, and the corneal displacement is clearly differentiable from potential noise or minor artifacts. Therefore, an accuracy of the IOP measurement using such a signal is very high. Moreover, the aforesaid tonometer is compact, easy to use, cost-efficient, accurate and reliable.

[0019] As an example, a tonometer is configures to send an air puff (air pulse, impulse or continuous constant air flow) towards an eye of the use. This air puff exerts a force on a cornea of the eye and pushes the cornea towards a retina of the eye. When the air puff is removed from the eye, the cornea bounces back towards its normal position (as the force exerted by the air puff is removed) due to its elastic properties. Thus, an oscillatory motion of the cornea begins, wherein the cornea often overshoots its normal position at a beginning of the oscillatory motion and continues to oscillate back and forth until these corneal oscillations are dampened out completely (and the cornea returns to its normal position). A frequency of the corneal oscillations is used to determine the IOP. An accuracy of the IOP determination depends on how strong the corneal oscillations are and how accurately the frequency of the corneal oscillations is determined. These corneal oscillations are referred as free corneal oscillations as there is no external forces affecting the oscillations after removing the air buff.

[0020] One problem experienced with above set up is that in many instances, the corneal oscillations that are produced are weak or almost negligible, and thus it is not possible to derive their frequency accurately. Thus, in such instances, the IOP cannot be accurately determined based on the corneal oscillations. The existing methods of IOP measurement using tonometers also lack reproducibility and accuracy. We have found out that for proper functionality it is important to control removal stage of the air buff (i.e. the ending edge). If air is removed too slowly, no oscillations (or very little) oscillations take place and thus IOP cannot be determined.

[0021] Indeed, in the tonometer described herein, the rapid removal of the air pressure (from corneal surface) during the second time period enables the cornea to oscillate freely that means that the influence of the ending air pulse to the oscillation parameters such as amplitude, frequency or damping factor is minimal. In other words, the signal captures the cornea's natural dynamic vibrational response. This way the measured signal describes mainly the properties of the eye minimizing the distortion by the ending air pulse resulting in more accurate IOP readings.

[0022] In a second aspect, the present disclosure provides a method for measuring intraocular pressure of an eye with a tonometer, the method comprising:

[0023] - aligning the tonometer with respect to the eye;

[0024] - providing an excitation air pulse towards a cornea of the eye during a first time period, wherein the provided excitation air pulse has a first intensity at an end time of the first time period, and this intensity is reduced from the first intensity to a second intensity during a second time period, wherein the second time period is after the first time period, for producing corneal oscillations;

[0025] - measuring a signal related to the corneal oscillations; and

[0026] - determining the intraocular pressure from the measured signal.

[0027] The present disclosure provides the aforementioned method, which enables production of strong corneal oscillations for accurately measuring the intraocular pressure. Proper alignment of the tonometer with respect to the eye ensures safe operation of the tonometer and better control over provision of the excitation air pulse, which in turn enables accurate measurement of the signal related to the corneal oscillations. The excitation air pulse is beneficially rapidly removed from the cornea of the eye during the second time period, for rapidly reducing the intensity of the excitation air pulse (from the first intensity to the second intensity). This rapid reduction of intensity enables strong corneal oscillations, which in turn, enable accurate measurement of the signal related to the corneal oscillations, and accurate determination of the intraocular pressure. The method described herein is simple, easily to implement, and accurately determines the intraocular pressure since the measured signal corresponds to strong oscillations which capture the smallest of changes in corneal displacement, and the corneal displacement is clearly differentiable from potential noise or minor artifacts.

[0028] Throughout the present disclosure, the term "tonometer" refers to a medical device that in use, measures the intraocular pressure of the eye. The "intraocular pressure" of the eye is a fluid pressure inside the eye. This fluid pressure is exerted by a vitreous fluid inside an eye chamber that retains a shape of the eye, provides support to a retina of the eye, and acts as a shock absorber, protecting delicate structures of the eye from external forces. Measuring the intraocular pressure (IOP) is essential in determining and assessing a health condition of the eye and such measuring is carried out by the tonometer. It will be appreciated that the tonometer described herein is easy-to-use, and enables safe, accurate, quick, and reliable IOP measurement.

[0029] Throughout the present disclosure, the term "air pulse generator" refers to a component of the tonometer that is controllable to produce the excitation air pulse which is directed towards the cornea of the eye when measuring the IOP. The "excitation air pulse" is a quick and controlled beam of pressurized air. The excitation air pulse is capable of exerting a force on a surface of the cornea (i.e., a corneal surface) of the eye upon incidence on said surface. Notably, this force depends on a pressure of the excitation air pulse, a velocity of the excitation air pulse, a width of the excitation air pulse, and the like. It will be appreciated that the air pulse generator is small-sized and compact for easily being arranged in the tonometer, and effectively produces the excitation air pulse according to requisite parameter(s). Structurally air pulse generator can comprise a pressure chamber and controllable valve and nozzle arrangement to provide air from the pressure chamber as an air impulse.

[0030] Throughout the present disclosure, the term "corneal oscillation measurement sensor" refers to a sensor that is configured to detect and measure the corneal oscillations induced at the corneal surface by the excitation air pulse. The corneal oscillation measurement sensor is configured to measure one or more characteristics of the corneal oscillations, and to transmit sensor data corresponding to said measurement to the controller. Optionally, the one or more characteristics of the corneal oscillations that are measured by the corneal oscillation measurement sensor comprise one or more of: an amplitude, a frequency, a damping factor, a duration, a phase, a value corresponding to peak-to-peak amplitude, of the corneal oscillations. The amplitude of the corneal oscillations is a displacement of an apex of the cornea from its normal position. It will be appreciated that measurement of other characteristics of the corneal oscillations is also feasible. The corneal oscillation measurement sensor is arranged in the tonometer such that it accurately measures the signal related to the corneal oscillations.

[0031] Optionally, the corneal oscillation measurement sensor is one of: a confocal chromatic sensor, a laser displacement sensor, a camera, an optical coherence tomography (OCT)-based sensor, an ultrasonic sensor. A technical effect of employing one of such sensors as the corneal oscillation measurement sensor is that such sensors are accurate, reliable, compact, cost-effective, and easy to implement. Furthermore, such sensors are capable of detecting and measuring the corneal oscillations which are of a very small magnitude (i.e., a very small amplitude). It will be appreciated that the confocal chromatic sensor, the OCT-based sensor, and the ultrasonic sensor are well-known in the art.

[0032] Throughout the present disclosure, the term "controller" refers to a computational device that is operable for controlling the overall operation of the tonometer. The controller may be implemented as an internal component of the tonometer, an external component of the tonometer, or a combination thereof. The controller may be any one of an embedded microcontroller, a microprocessor, a field-programmable gate array (FPGA), digital signal processor (DSP), an application-specific integrated circuit (ASIC), a programmable logic circuits, an on-the chip control system, and any other suitable control module. The controller may be communicably coupled to the air pulse generator and the corneal oscillation measurement sensor wirelessly, in a wired manner, or in any combination thereof. The controller is configured to control the air pulse generator by adjusting at least the first time period of providing the excitation air pulse towards the eye and the second time period of removing the excitation air pulse from the eye, to accurately measure the IOP of the eye. The controller may also control other parameter(s) of the excitation air pulse by controlling the air pulse generator. The controller is also configured to receive the signal from the corneal oscillation measurement sensor pertaining to the corneal oscillations, to process information available in the received signal, and to determine the IOP of the eye.

[0033] The controller, when in use, controls the air pulse generator to generate the excitation air pulse and to send the excitation air pulse to the cornea in a specific manner. Notably, the excitation air pulse is sent to the cornea during the first time period, so an intensity of the excitation air pulse at the cornea increases from zero (at a start time of the first time period) to the first intensity (at the end time of the first time period). Herein, the "intensity" of the excitation air pulse at the cornea refers to an intensity of pressure exerted by the excitation air pulse on the cornea. Said pressure pushes the cornea towards a retina of the eye. In other words, the intensity of the excitation air pulse displaces the corneal surface inwards into the eye. In an example, the intensity of the excitation air pulse at the cornea may increase linearly during the first time period. In another example, the intensity of the excitation air pulse at the cornea may increase linearly during a first part of the first time period, and may remain constant during a remaining part of the first time period. The increase can be also non-linear or ramp type.

[0034] Furthermore, the controller controls the air pulse generator to stop sending the excitation air pulse to the cornea, during the second time period. The second time period is after the first time period, meaning that the end time of the first time period is a start time of the second time period). The sending of the excitation air pulse is stopped during the second time period, so that the intensity of the excitation air pulse at the cornea reduces from the first intensity to the second intensity during the second time period. In other words, the excitation air pulse is removed from the cornea during the second time period, thereby reducing the pressure exerted by the excitation air pulse on the cornea. When said pressure is reduced, the cornea rebounds and moves away from the retina towards its normal position. This movement of the cornea towards the retina and then away from the retina constitutes a corneal oscillation. It will be appreciated that several corneal oscillations occur and gradually decrease in amplitude due to damping effects of biomechanical properties of a tissue of the cornea. When the oscillations dampen out completely, the cornea returns to its normal position. The second time period is selected such that the intensity of the excitation air pulse on the cornea is reduced very fast, thereby triggering strong corneal oscillations (i.e., corneal oscillation having high amplitudes). It will be appreciated that the aforesaid manner of rapidly stopping the sending of the excitation air pulse to the cornea beneficially enables in producing strong corneal oscillations, as the cornea rapidly bounces back in a strong oscillatory motion. If the sending of the excitation air pulse is stopped slowly, the cornea returns slowly to its normal position, and therefore weak or almost negligible corneal oscillations are produced. Thus, the tonometer of the present disclosure effectively overcomes the aforesaid problem of producing too small oscillations for reliable measurement, by rapidly reducing the intensity of the excitation air pulse in the second time period, for producing strong corneal oscillations.

[0035] Optionally, the first time period is within a range of 1 to 15 msec milliseconds. For example, the first time period may be from 1 msec, 2 msec, 3 msec, 4 msec, 5 msec, 6 msec, 7 msec, 8 msec, 9 msec, 10 msec, 11 msec, 12 msec, 13 msec, 14 msec, or up to 1 msec, 2 msec, 3 msec, 4 msec, 5 msec, 6 msec, 7 msec, 8 msec, 9 msec, 10 msec, 11 msec, 12 msec, 13 msec, 14 msec, or up to 15 msec. A technical effect of the first time period being within the aforesaid range is that it minimizes discomfort for a user of the tonometer (since the pressure exerted by the excitation air pulse on the cornea is not for too long), and enables quick response of the cornea for accurate and quick measurement of the IOP. According to one embodiment the first time period can be arbitrary long as the oscillations are initiated after the first time period. As an example first time period can be 10, 20, 30, 40, 50, 60, 70, 80, 90, 100 msec or longer. Optionally, the second time period is less than 3 msec. For example, the second time period may be less than 3.0 msec, 2.9 msec, 2.8 msec, 2.7 msec, 2.6 msec, 2.5 msec, 2.4 msec, 2.3 msec, 2.2 msec, 2.1 msec, 2.0 msec, 1.9 msec, 1.8 msec, 1.7 msec, 1.6 msec, 1.5 msec, 1.4 msec, 1.3 msec, 1.2 msec, 1.1 msec, 1.0 msec, 0.9 msec, 0.8 msec, 0.7 msec, 0.6 msec, 0.5 msec, 0.4 msec, 0.3 msec, 0.2 msec, 0.1 msec, or down to 0 msec. Alternatively the second time period can be between 0 msec, 0.1 msec, 0.2 msec, 0.3 msec, 0.4 msec, 0.5 msec, 0.6 msec, 0.7 msec, 0.8 msec, 0.9 msec, 1.0 msec, 1.1 msec, 1.2 msec, 1.3 msec, 1.4 msec, 1.5 msec, 1.6 msec, 1.7 msec, 1.8 msec, 1.9 msec, 2.0 msec, 2.1 msec, 2.2 msec, 2.3 msec, 2.4 msec, 2.5 msec, 2.6 msec, 2.7 msec, 2.8 msec, 2.9 msec upto 0.1 msec, 0.2 msec, 0.3 msec, 0.4 msec, 0.5 msec, 0.6 msec, 0.7 msec, 0.8 msec, 0.9 msec, 1.0 msec, 1.1 msec, 1.2 msec, 1.3 msec, 1.4 msec, 1.5 msec, 1.6 msec, 1.7 msec, 1.8 msec, 1.9 msec, 2.0 msec, 2.1 msec, 2.2 msec, 2.3 msec, 2.4 msec, 2.5 msec, 2.6 msec, 2.7 msec, 2.8 msec, 2.9 msec, 3.0 msec . This means that the second time period is very short, and thus the intensity reduction from the first intensity to the second intensity occurs very quickly. A technical effect of the second time period being within the aforesaid range is that it allows for quick removal of the excitation air pulse from the cornea, thereby producing strong corneal oscillations. Upon the quick removal of the excitation air pulse from the cornea, the pressure exerted on the cornea reduces rapidly (i.e., is released rapidly), and thus allows the cornea to return from its pressure-displaced position to its normal position via damping corneal oscillation. The quick removal of the excitation air pulse enables the cornea to oscillation freely without external disruption of the otherwise decaying air pulse.

[0036] Optionally, the second time period is less than l / 2th of a time period of a single cycle of the corneal oscillations. In this regard, the second time period is a fraction of the single cycle of the corneal oscillations, which means that the second time period is very short. A short second time period enables quick removal of the excitation air pulse from the cornea, thereby producing strong corneal oscillations. Beneficially, the short second time period allows to avoid the problem of residual airflow damping (i.e., decaying) an amplitude of the corneal oscillations. This preserves the integrity of the signal used for intraocular pressure (IOP) measurement. As a result, a more accurate IOP measurement is enabled from the cornea's natural vibrational response (which is measured as the signal related to the corneal oscillations). For example, the second time period may lie from l / 2th to l / 10th of the time period of the single cycle of the corneal oscillations. For example, a frequency of the corneal oscillations may be 200 Hertz, so the time period of the single cycle of the corneal oscillations may be 5 milliseconds. In this example, the second time period may be l / 4th of the time period of the single cycle of the corneal oscillations, so the second time period may be 1.25 milliseconds. In another example if the second time period is l / 2th then the duration of the second time period would be less than 2.5msec.

[0037] Furthermore, in the above regard, it will be appreciated that the tonometer employs an innovative measurement principle. In said principle, the IOP is calculated from a dynamic response of the cornea, specifically its natural oscillations following excitation. This approach requires precise excitation conditions (such as controlling the air pulse generator in such a way that the second time period is less than l / 2th of the time period of the single cycle of the corneal oscillations) to ensure the cornea is left free to oscillate without interference, allowing a clear and reliable signal to be captured. In this way, timing characteristics of the air pulse termination are precisely optimized for enhancing oscillation-based signal measurement. This temporal constraint of the second time period ensures that the trailing edge of the air pulse does not interfere with or attenuate the corneal oscillations, which is essential to preserve signal amplitude and measurement integrity. If the pulse is longer it might lead to interference of the oscillations, due to residual air, thus the measurement might not provide reliable results.

[0038] Optionally, the time period of the single cycle of the corneal oscillations lies in a range of 1 millisecond to 20 milliseconds. For example, the time period of the single cycle of the corneal oscillations may be from 1, 2, 3, 5, 7, 9, 12, or 16 milliseconds up to 4, 8, 12, 15, 17, 18, 19, or 20 milliseconds. For example, in this regard, the frequency of the corneal oscillations may be in a range of 50 Hertz to 1000 Hertz.

[0039] Optionally, a ratio between the second intensity to the first intensity is between 0 to 0.5. For example, the ratio between the second intensity to the first intensity may be from 0, 0.05, 0.1, 0.2, or 0.3 up to 0.25, 0.4, 0.45, or 0.5. This means that the second intensity is equal to or less than half of the first intensity. In other words, the first intensity reduces considerably (by at least 50% up to 100%) during the second time period. A technical effect of the ratio between the second intensity to the first intensity lying between the aforesaid range is that the pressure exerted by the excitation air pulse on the cornea reduces drastically within the second time period, which enables the cornea to quickly return to its normal position, thereby producing strong (i.e., high-amplitude) corneal oscillations. In other words, smaller the ratio between the second intensity to the first intensity, greater is the reduction in intensity (of the excitation air pulse on the cornea) during the second time period, and thus stronger are the corneal oscillations.

[0040] As an example, for a same second time period, the ratio between the second intensity to the first intensity may be 0 in a first case (i.e., the intensity may reduce such that the second intensity is zero) and may be 0.3 in a second case (i.e., the intensity may reduce such that the second intensity is 30 percent of the first intensity). This means that the reduction in intensity is more drastic in the first case, as compared to the second case. Thus, an amplitude of the corneal oscillations produced in the first case may be higher than an amplitude of the corneal oscillations produced in the second case.

[0041] Optionally, the second time period is function of the ratio. This means that the second time period may depend on the ratio between the second intensity to the first intensity. Optionally, in this regard, smaller the ratio between the second intensity to the first intensity, shorter is the second time period, and vice versa. When the ratio is small, it means that a high reduction in intensity (from the first intensity to the second intensity) is to be achieved, and when the second time period is correspondingly selected to be short, this high reduction in intensity is achieved very quickly. As a result, strong corneal oscillations are produced very quickly, leading to an accurate measurement of the IOP. As an example if the ratio (i.e. difference between the second and the first) is small the second period must be smaller than if the ratio is high. For example first intensity is 100 units and second is 25 units (ratio 25 / 100 = 0.25) then the second time period should not exceed as an example 3.5msec x (1-0.25) = 2.6 msec. If the first intensity is 100 units and second is 10 units then the second time period should not exceed as an example 3.6msec x (1-0.1) = 3.15msec

[0042] The controller controls the corneal oscillation measurement sensor to measure the signal related to the corneal oscillations. The measurement may be started from a start time of the first time period, for a predefined time duration. As an example, the predefined time duration may be 5- 100 times of the single cycle of the corneal oscillations. Optionally, the signal related to the corneal oscillations is a signal related to a displacement (i.e., a deformation) of the cornea. The controller receives the measured signal from the corneal oscillation measurement sensor. Indeed it is sufficient to measure in some cases only one cycle if the signal to noise ratio is sufficient to find duration of oscillation period. Optionally, a peak amplitude of the corneal oscillations lies in a range of 0.5 to 100 micrometers. As an example range from 0 pm, 5 pm, 10 pm, 15 pm, 20 pm, 25 pm, 30 pm, 35 pm, 40 pm, 45 pm, 50 pm, 55 pm, 60 pm, 65 pm, 70 pm, 75 pm, 80 pm, 85 pm, 90 pm, 95 pm, up to 5 pm, 10 pm, 15 pm, 20 pm, 25 pm, 30 pm, 35 pm, 40 pm, 45 pm, 50 pm, 55 pm, 60 pm, 65 pm, 70 pm, 75 pm, 80 pm, 85 pm, 90 pm, 95 pm, and 100 pm. When the peak amplitude of the corneal oscillations lies in the aforesaid range, the IOP can be determined accurately from the measured signal related to the corneal oscillations. The peak amplitude of the corneal oscillations beneficially lies in the aforesaid range due to the rapid reduction in the intensity of the excitation air pulse from the first intensity to the second intensity, during the second time period. Needed peak to peak amplitude depends on the used corneal oscillation measurement sensor and its accuracy. As an example, confocal chromatic sensor might be able to detect movements of sub micrometer range. On the other hand, ultrasonic sensor might require larger oscillations to provide sufficient signal.

[0043] Optionally, the peak amplitude of the corneal oscillations is less than an applanation point. The applanation point is that point at which the corneal surface is flattened. A technical effect of the peak amplitude of the corneal oscillations being less than the applanation point is that it prevents discomfort for the user, prevents damage to the eye, and improves an accuracy of the IOP measurement. If the peak amplitude is less than applanation point also a smaller diameter air impulse (at surface of cornea) than in "conventional" applanation based tonometer (should those use air buff for deformation) is sufficient.

[0044] The controller determines the IOP from the measured signal, by employing at least one of: an algorithm, a model, a formula, reference data, or similar, for processing the measured signal. The reference data could be historical usage data, simulation data, experimental data, or similar, which relates the measured signal to a value of the IOP. A technical effect of calculating the IOP in such a manner is that it is determined accurately, reliably, and quickly.

[0045] Optionally, when determining the intraocular pressure from the measured signal, the controller is configured to: determine a frequency of the corneal oscillations, from the measured signal; and calculate the intraocular pressure, based on the frequency.

[0046] In this regard, the "frequency of corneal oscillations" refers to a frequency at which the cornea oscillates after being deformed by the excitation air pulse (i.e. after the excitation air pulse is stopped). The frequency of the corneal oscillations is equal to a resonance frequency of the cornea (i.e., a natural frequency at which the cornea vibrates or oscillates in response to an external force such as the excitation air pulse). The frequency of the corneal oscillations is a function of the IOP. Optionally, the controller is configured to employ at least one signal processing algorithm to determine the frequency of corneal oscillations, from the measured signal. Thereafter, the controller optionally employs at least one of: a function, a reference data, or similar, to calculate the IOP, based on the frequency. As an example, the frequency of corneal oscillations may be 455 Hertz, and the IOP may be 30 mmHg. As another example, the frequency of corneal oscillations may be 390 Hertz, and the IOP may be 20 mmHg. A technical effect of determining the IOP in this manner is that the IOP is determined accurately, reliably, and quickly. Notably, employing the frequency of the corneal oscillations enhances an accuracy and reliability when calculating the IOP, as said frequency is directly influenced by the internal pressure of the eye.

[0047] Optionally, the air pulse generator comprises: a pressure chamber, a nozzle, and a valve arranged between the pressure chamber and the nozzle, wherein when controlling the air pulse generator, the controller is configured to: open the valve for the first time period so that pressured air stored in the pressure chamber exits the pressure chamber to enter the nozzle, and is directed by the nozzle towards the cornea of the eye, wherein the pressured air constitutes the excitation air pulse; and close the valve during the second time period, wherein the second time period starts at the end time of the first time period.

[0048] In this regard, a technical effect of closing the valve during the second time period is that the excitation air pulse is effectively removed from the cornea during the second time period, for producing strong corneal oscillations. The second time period is selected to be such that the valve is closed quickly, triggering a rapid return of the cornea from its pressure- displaced position to its normal position. The air pulse generator described above is therefore controllable to quickly remove the excitation air pulse from the cornea, for enabling production of strong corneal oscillations, which further enable accurate IOP measurement. Such an air pulse generator is inexpensive, easy to manufacture, easily arranged in the tonometer, and easy to use. Each of the components of the air pulse generator are described in more detail below.

[0049] Throughout the present disclosure, the term "pressure chamber" is an enclosed space or a reservoir within the air pulse generator where the pressured air (i.e., pressurized air) is stored. Optionally, the pressured air is stored at a predefined pressure, within the pressure chamber. The predefined pressure is main parameter affecting the intensity of the air pulse at corneal. Other parameters affecting it is for example size of exit aperture of a nozzle which is directed towards the eye when in use. Intensity can be expressed in number of air molecules per second per area which hits the cornea. In practice this can be expressed as pressure introduced by the air impulse to the corneal surface. Optionally, in this regard, the predefined pressure inside is greater than the first intensity. Optionally, the predefined intensity lies between 0.5 to 10 bars. In some embodiments, the pressured air is directly provided into the pressure chamber, by a source of high pressure air, via an inlet of the pressure chamber that is connected to said source. In some other embodiments, the air pulse generator further comprises a pressure generator that generates the predefined intensity of the pressured air inside the pressure chamber. Example of the pressure generator may include, but are not limited to, a reciprocating air compressor, a rotary screw air compressor, a centrifugal air compressor, and an air pump. Optionally, the air pulse generator further comprises a pressure regulator that maintains an intensity of the pressured air within the pressure chamber at the predefined intensity. Optionally, the air pulse generator further comprises a pressure sensor for sensing the intensity of the pressured air within the pressure chamber. When the sensed intensity of the pressured air within the pressure chamber lies out of the aforesaid range of the predefined intensity, the controller controls the pressure regulator to increase or decrease the pressure of the pressured air within the pressure chamber such that the predefined intensity of pressure is maintained.

[0050] Throughout the present disclosure, the term "nozzle" refers to a device that controls a flow direction of the excitation air pulse. The nozzle has an input aperture through which the pressured air stored in the pressure chamber enters the nozzle when the valve is open, and an exit aperture through which the excitation air pulse exits the nozzle towards the cornea. In other words, the nozzle directs the excitation air pulse towards the cornea. Optionally, the exit aperture is arranged along a principal axis of measurement of the corneal oscillation measurement sensor. This beneficially enables accurate measurement of the signal related to the corneal oscillations, and thus enables accurate IOP measurement.

[0051] Throughout the present disclosure, the term "valve" refers to a mechanical device located between the pressure chamber and the nozzle, which is capable of swift opening and closing. A primary function of the valve is to control a flow of pressured air from the pressure chamber to the nozzle. The valve is opened (during the first time period) and closed (during the second time period) in a precise manner, by the controller. It is important that the valve be closed at least partially within the second time period, so that the pressure at the cornea can be reduced within the second time period, for producing the corneal oscillations.

[0052] Optionally, the valve is one of: an electrostatic microvalve, a piezoelectric microvalve, a thermo-pneumatic microvalve, an electromagnetic microvalve, a microelectromechanical systems (MEMS) microvalve. As an example, the electromagnetic microvalve may be a solenoid microvalve. Each of the aforesaid valves has a high switching speed (for example, of the order of a few microseconds), so a technical effect of employing the one of the aforesaid valves in the air pulse generator is that such the valve can be efficiently and precisely opened and closed for the first time period and the second time period, respectively, for producing the corneal oscillations.

[0053] The present disclosure also relates to the method as described above. Various embodiments and variants disclosed above, with respect to the aforementioned tonometer, apply mutatis mutandis to the method.

[0054] The step of aligning the tonometer with respect to the eye is important as it enables safe operation of the tonometer for obtaining accurate IOP measurements. The step of aligning the tonometer may be performed manually (for example, by the user, by a medical practitioner, or similar), semi-automatically (for example, using an alignment means, an ophthalmic device, or similar), or fully-automatically (for example, using a robot). Optionally, the tonometer comprises an alignment element for enabling proper alignment of the tonometer with respect to the eye.

[0055] Optionally, in the method, the second time period is less than 3.5msec. Optionally, in the method, the step of determining the intraocular pressure from the measured signal comprises: determining a frequency of the corneal oscillations, from the measured signal; and calculating the intraocular pressure, based on the frequency.

[0056] In general after (and during) impact from air impulse the corneal surface starts to oscillate based on motion of laws. Higher the force of the impact more the cornea deforms (towards retina). When the force (pressure i.e. the intensity of the air pulse) is removed the eye starts free oscillations. The oscillation frequency is function of IOP. The function can be determined by experiments or by modelling.

[0057] DETAILED DESCRIPTION OF THE DRAWINGS

[0058] Referring to FIG. 1, illustrated is a schematic representation of a tonometer 100 used for measuring intraocular pressure of an eye 150, in accordance with an embodiment of the present disclosure. The tonometer 100 comprises an air pulse generator 102, a corneal oscillation measurement sensor 104, and a controller 106 communicably coupled to the air pulse generator 102 and the corneal oscillation measurement sensor 104. The controller 106 is configured to: control, when in use, the air pulse generator 102 to provide an excitation air pulse 108 towards a cornea 152 of the eye 150 during a first time period, wherein the provided excitation air pulse 108 has a first intensity at an end time of the first time period, and this intensity is reduced from the first intensity to a second intensity during a second time period, wherein the second time period is after the first time period, for producing corneal oscillations; measure a signal related to the corneal oscillations, using the corneal oscillation measurement sensor 104, and determine the intraocular pressure from the measured signal. It may be understood by a person skilled in the art that FIG. 1 includes a simplified illustration of the tonometer 100 and its components for sake of clarity only, which should not unduly limit the scope of the claims herein. The person skilled in the art will recognize many variations, alternatives, and modifications of embodiments of the present disclosure.

[0059] Referring to FIG. 2, illustrated is a schematic representation of the air pulse generator 102 of the tonometer 100 of FIG. 1, in accordance with an embodiment of the present disclosure. The air pulse generator 102 comprises a pressure chamber 202, a nozzle 204, and a valve 206 arranged between the pressure chamber 202 and the nozzle 204, wherein when controlling the air pulse generator 102, the controller 106 (not shown in FIG. 2) of the tonometer 100 is configured to: open the valve 206 for the first time period so that pressured air stored in the pressure chamber 202 exits the pressure chamber 202 to enter the nozzle 204, and is directed by the nozzle 204 towards the cornea 152 of the eye 150 (as shown in FIG. 1), wherein the pressured air constitutes the excitation air pulse 108 (as shown in FIG. 1); and close the valve 206 during the second time period, wherein the second time period starts at the end time of the first time period.

[0060] It may be understood by a person skilled in the art that FIG. 2 includes a simplified illustration of the air pulse generator 102 and its components for sake of clarity only, which should not unduly limit the scope of the claims herein. The person skilled in the art will recognize many variations, alternatives, and modifications of embodiments of the present disclosure. For example, the air pulse generator 102 may further comprise a pressure sensor 208 and a pressure regulator 210 arranged in the pressure chamber 202.

[0061] Referring to FIG. 3, illustrated is a first graphical representation 300A of a variation of an intensity of excitation air pulse at a cornea of an eye with respect to time, and a second graphical representation 300B of a variation of a displacement of an apex of the cornea with respect to time, in accordance with an embodiment of the present disclosure. As shown in the first graphical representation 300A, values of the intensity of the excitation air pulse at the cornea of the eye are plotted on Y-axis, whereas the time is plotted on X-axis. In the second graphical representation 300B, values of the displacement of the apex of the cornea are plotted on Y-axis, whereas the time is plotted on X-axis. The values of the displacement could be negative, positive, or zero, wherein negative values indicate that the apex of the cornea is pushed inwards towards a retina of the eye, positive values indicate that the apex of the cornea is pushed outwards away from the retina, and zero value means that the apex of the cornea is at its normal position.

[0062] In the first graphical representation 300A, it is shown (for example as solid lines 302 and 304) that during a first time period T1 when the excitation air pulse is provided towards the cornea, the intensity of the excitation air pulse increases from 0 to a first intensity I, and then remains constant at the first intensity I till an end time Tie of the first time period Tl. After the first time period Tl, a second time period T2 begins. During the second time period T2, the intensity of the excitation air pulse on the cornea is reduced from the first intensity I to a second intensity. In a first example, the first intensity I reduces to a second intensity that is equal to zero, as shown by a long-dash line 306. In a second example, the first intensity I reduces to a second intensity that is equal to 0.31, as shown by a short-dash line 308. As shown by the first and second examples, a ratio between the second intensity to the first intensity may optionally be between 0 to 0.5.

[0063] Correspondingly, in the second graphical representation 300B, there are shown corneal oscillations which are produced when the excitation air pulse is provided to the cornea in the manner described above. During the first time period Tl, as the intensity of the excitation air pulse increases from 0 to a first intensity I, a magnitude of the displacement increases from 0 to -D (shown by line 310 with a negative slope) as the cornea gets pushed inwards towards the retina of the eye by an increasing pressure exerted by the excitation air pulse on the cornea. The negative sign of the displacement value -D indicates the inward pushing of the cornea. Then, when the intensity remains constant at the first intensity I till an end time Tie of the first time period Tl, the displacement also remains constant at -D (shown by line 312). Next, as the intensity reduces from the first intensity I to the second intensity during the second time period T2, different corneal oscillations are observed. Upon such intensity reduction, the cornea rapidly moves away from the retina in an oscillatory motion, to finally return to its normal position when the oscillatory motion is fully damped. This movement is shown by a change in a direction of displacement after the end time Tie. While in the oscillatory motion, the apex often overshoots its normal position, and this is depicted by positive values of the displacement. Referring to the first example, corneal oscillations 320 (shown by a long- dash curve) are produced when the second intensity is equal to zero. Referring to the second example, corneal oscillations 330 (shown by a short-dash curve) are produced when the second intensity is equal to 0.31. For example, as shown, a peak amplitude Dip of the corneal oscillations 320 is greater than a peak amplitude D2p of the corneal oscillations 330, since the intensity reduction during the second time period T2 is greater in the first example, as compared to the second example. Strong corneal oscillations with high peak amplitudes enable accurate calculation of the intraocular pressure.

[0064] From the first and second graphical representations 300A and 300B, it is also shown that the second time period T2 may optionally lie within a range of l / 2th - l / 8th of a time period of a single cycle of the corneal oscillations 320 and 330. The second time period T2 optionally lies within a range of which is less than 3msec A short duration of the second time period T2 during which the intensity reduction occurs, enables in producing the strong corneal oscillations which are free from problems such as damping due to residual airflow. Such strong corneal oscillations result in high signal integrity and subsequently, a more accurate IOP measurement.

[0065] It may be understood by a person skilled in the art that FIG. 3 is merely an example for sake of clarity, which should not unduly limit the scope of the claims herein. The person skilled in the art will recognize many variations, alternatives, and modifications of embodiments of the present disclosure.

[0066] Referring to FIG. 4, illustrated is a graphical representation of intraocular pressure as a function of corneal frequency, in accordance with an embodiment of the present disclosure. As shown, values of the intraocular pressure are plotted on an X-axis, whereas values of the corneal frequency are plotted on a Y-axis. As shown, with an increase in the corneal frequency, values of the intraocular pressure also increase.

[0067] It may be understood by a person skilled in the art that FIG. 4 is merely an example for sake of clarity, which should not unduly limit the scope of the claims herein. The person skilled in the art will recognize many variations, alternatives, and modifications of embodiments of the present disclosure.

[0068] Referring to FIG. 5, illustrated is a flowchart depicting steps of a method for measuring intraocular pressure of an eye with a tonometer, in accordance with an embodiment of the present disclosure. At step 502, the tonometer is aligned with respect to the eye. At step 504, an excitation air pulse is provided towards a cornea of the eye during a first time period, wherein the provided excitation air pulse has a first intensity at an end time of the first time period, and this intensity is reduced from the first intensity to a second intensity during a second time period, wherein the second time period is after the first time period, for producing corneal oscillations. At step 506, a signal related to the corneal oscillations is measured. At step 508, the intraocular pressure is determined from the measured signal.

[0069] The aforementioned steps are only illustrative and other alternatives can also be provided where one or more steps are added, one or more steps are removed, or one or more steps are provided in a different sequence without departing from the scope of the claims herein.

Claims

CLAIMS1. A tonometer (100) for measuring intraocular pressure of an eye (150), the tonometer comprising: an air pulse generator (102), a corneal oscillation measurement sensor (104), and a controller (106) communicably coupled to the air pulse generator and the corneal oscillation measurement sensor, wherein the controller is configured to: control, when in use, the air pulse generator to provide an excitation air pulse (108) towards a cornea (152) of the eye during a first time period (Tl), wherein the provided excitation air pulse has a first intensity (I) at an end time (Tie) of the first time period, and this intensity is reduced from the first intensity to a second intensity during a second time period (T2), wherein the second time period is after the first time period, for producing corneal oscillations (320, 330); measure a signal related to the corneal oscillations, using the corneal oscillation measurement sensor; and determine the intraocular pressure from the measured signal.

2. A tonometer (100) according to claim 1, wherein the air pulse generator (102) comprises: a pressure chamber (202), a nozzle (204), and a valve (206) arranged between the pressure chamber and the nozzle, wherein when controlling the air pulse generator, the controller (106) is configured to: open the valve for the first time period (Tl) so that pressured air stored in the pressure chamber exits the pressure chamber to enter thenozzle, and is directed by the nozzle towards the cornea of the eye, wherein the pressured air constitutes the excitation air pulse (108); and close the valve during the second time period (T2), wherein the second time period starts at the end time (Tie) of the first time period.

3. A tonometer (100) according to claim 1 or 2, wherein the first time period (Tl) is within a range of 1-15 milliseconds.

4. A tonometer (100) according to any of the preceding claims, wherein the second time period (T2) is less than 3 milliseconds.

5. A tonometer (100) according to any of the claims 1-4, wherein the second time period (T2) is less than l / 2th of a time period of a single cycle of the corneal oscillations (320, 330).

6. A tonometer (100) according to claim 5, wherein the time period of the single cycle of the corneal oscillations (110) lies in a range of 1 millisecond to 20 milliseconds.

7. A tonometer (100) according to any of claims 2-6, wherein the valve (206) is one of: an electrostatic microvalve, a piezoelectric microvalve, a thermo-pneumatic microvalve, an electromagnetic microvalve, a microelectromechanical systems (MEMS) microvalve.

8. A tonometer (100) according to any of the preceding claims, wherein a ratio between the second intensity to the first intensity (I) is between 0 to 0.5.

9. A tonometer (100) according to claim 8, wherein the second time period (T2) is function of the ratio.

10. A tonometer (100) according to any of the preceding claims, wherein a peak amplitude (Dip, D2p) of the corneal oscillations (320, 330) lies in a range 0.5 to 100 micrometers.

11. A tonometer (100) according to any of the preceding claims, wherein the corneal oscillation measurement sensor (104) is one of: aconfocal chromatic sensor, a laser displacement sensor, a camera, an optical coherence tomography (OCT)-based sensor, an ultrasonic sensor.

12. A tonometer (100) according to any of the preceding claims, wherein when determining the intraocular pressure from the measured signal, the controller (106) is configured to: determine a frequency of the corneal oscillations (320, 330), from the measured signal; and calculate the intraocular pressure, based on the frequency.

13. A method for measuring intraocular pressure of an eye (150) with a tonometer (100), the method comprising:- aligning the tonometer with respect to the eye;- providing an excitation air pulse (108) towards a cornea (152) of the eye during a first time period (Tl), wherein the provided excitation air pulse has a first intensity at an end time of the first time period, and this intensity is reduced from the first intensity (I) to a second intensity during a second time period (T2), wherein the second time period is after the first time period, for producing corneal oscillations (320, 330);- measuring a signal related to the corneal oscillations; and- determining the intraocular pressure from the measured signal.

14. A method according to claim 13, wherein the second time period (T2) is less than 3msec.

15. A method according to claim 13 or 14, wherein the step of determining the intraocular pressure from the measured signal comprises: determining a frequency of the corneal oscillations (320, 330), from the measured signal; and calculating the intraocular pressure, based on the frequency.

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