Tonometers for measuring intraocular pressure of eye using air pulse

Abstract

Disclosed is a tonometer (100, 200, 300) for measuring intraocular pressure of an eye (108, 208, 302), the tonometer comprising an air pulse generator (102, 202) having an air exit element (104, 204); a displacement sensor (106, 310) for measuring deformations of the eye, wherein the displacement sensor has a principal axis (112, 212) of measurement, and wherein an exit interface (114, 214) of the air exit element is arranged along the principal axis of measurement; and a controller (110, 210) communicably coupled to the air pulse generator and the displacement sensor. The controller is configured to control the air pulse generator to generate an excitation air pulse (116, 236, 304) and control the air pulse generator to send the excitation air pulse towards the eye via the exit interface of air exit element, for producing deformations; measure a signal (308) related to the deformations, using displacement sensor; and determine intraocular pressure of the eye from the measured signal.

Description

[0001] TONOMETERS FOR MEASURING INTRAOCULAR PRESSURE OF EYE

[0002] USING AIR PULSE

[0003] TECHNICAL FIELD

[0004] The present disclosure relates to tonometers for measuring intraocular pressure of eyes. Moreover, the present disclosure relates to methods for measuring intraocular pressure of eyes with tonometers.

[0005] BACKGROUND

[0006] The accurate measurement of intraocular pressure (IOP) is pivotal in ophthalmic diagnostics. It serves as a fundamental parameter for assessing ocular health and detecting abnormalities, particularly in conditions such as glaucoma which causes damage to optic nerve leading to progressive vision impairment. A tonometer is an instrument that is used for measuring the IOP. Examples of the tonometer are, a rebound tonometer, a dynamic contour tonometer, a non-contact (Air-Puff) tonometer, and a Goldmann applanation tonometer (GAT). Nowadays, the non-contact (Air-Puff) tonometers are being adapted widely because such tonometers can provide quick, and contactless IOP measurement with reduced risk of infection and discomfort for a patient.

[0007] However, the existing tonometers lack accuracy due to inaccuracies in measuring the IOP. The existing tonometers are susceptible to unreliable IOP measurements in certain eye conditions or anatomical variations such as corneal irregularities, edema, variable corneal curvature, and variable corneal thickness. Further, the IOP measurements made by the existing tonometers tend to lack repeatability and consistency in measurement of the IOP.

[0008] In air puff tonometer the intensity of the air flow is slowly increased so that the cornea bends over the applanation state and then decreased so that the cornea returns to its normal state. IOP is measured at the applanation state so that optical methods define the applanation state and system registers how much force / intensity is needed to create the applanation. This has nothing to do with corneal oscillation of the invention. Conventional non-contact tonometers (air puff) are based on the Imbert-Fick principle that requires applanating the cornea from a reasonably large area (several millimeters in diameter). Therefore, in light of the foregoing discussion, there exists a need to overcome the aforementioned drawbacks.

[0009] SUMMARY

[0010] The aim of the present disclosure is to provide a tonometer for measuring intraocular pressure of an eye, and a method for measuring intraocular pressure of an eye to enable diagnosis of eye condition of the eye in a non-invasive and accurate manner. The aim of the present disclosure is achieved by a tonometer for measuring intraocular pressure of an eye, and a method for measuring intraocular pressure of an eye as defined in the appended independent claims to which reference is made to. Advantageous features are set out in the appended dependent claims.

[0011] 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.

[0012] Indeed present disclosure is not based on the Imbert-Fick principle and applanation state is not needed. Instead, we disclose using a gentle air impulse to displace the cornea from its normal position. After the impulse the cornea starts to oscillate as a damped harmonic oscillator returning to the normal state and IOP (intra ocular pressure) is defined from the oscillation signal. In this way, the IOP is determined accurately and reliably, since a mechanical response of the corneal surface is leveraged for the IOP measurement. Because present disclosure is not based on applanation, it is technically more easier to implement and is more comfortable for the patient. One benefit of the disclosed air pulse tonometer is that it causes less pain and less discomfort for the patient than traditional air puff tonometers.

[0013] BRIEF DESCRIPTION OF THE DRAWINGS

[0014] FIG. 1 illustrates a schematic illustration of a tonometer, in accordance with an embodiment of the present disclosure;

[0015] FIG. 2 illustrates an exemplary schematic illustration of a tonometer, in accordance with an embodiment of the present disclosure;

[0016] FIG. 3A illustrate an exemplary schematic diagram of an implementation of a tonometer for measuring an intraocular pressure value of an eye, in accordance with an embodiment of the present disclosure;

[0017] FIG. 3B illustrates a graphical representation of an intraocular pressure value as a function of corneal frequency, in accordance with an embodiment of the present disclosure;

[0018] FIG. 4 illustrates steps of a method for measuring intraocular pressure of an eye with a tonometer, in accordance with an embodiment of the present disclosure; and

[0019] FIG. 5 illustrates deformations associated with a frequency sweep of air pulses, in accordance with an embodiment of the present disclosure.

[0020] DETAILED DESCRIPTION OF EMBODIMENTS

[0021] 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.

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

[0023] - an air pulse generator having an air exit element;

[0024] - a displacement sensor for measuring deformations of the eye, wherein the displacement sensor has a principal axis of measurement, and wherein an exit interface of the air exit element is arranged along the principal axis of measurement; and

[0025] - a controller communicably coupled to the air pulse generator and the displacement sensor, wherein the controller is configured to: control the air pulse generator to generate an excitation air pulse and control the air pulse generator to send the excitation air pulse towards the eye via the exit interface of the air exit element, for producing the deformations; measure a signal related to the deformations, using the displacement sensor; and determine the intraocular pressure of the eye from the measured signal.

[0026] The present disclosure provides the aforementioned first aspect to measure the intraocular pressure (IOP) of the eye without making any direct contact with the eye, and from a same point where the excitation air pulse is incident on the eye. Herein, generating the excitation air pulse reduces a risk of contamination and discomfort in the eye. The tonometer is configured in such a manner that the exit interface of the air exit element is arranged in a co-centric manner with the displacement sensor, i.e., along the principal axis of measurement, such that the signals related to the deformations are measured from the same point where the excitation air pulse is sent towards the eye. Such alignment in the eccentric manner eliminates errors due to spatial misalignment, thus providing characterization of a dynamic quantifiable biomechanical corneal response. In this way, accurate IOP can be measured, which leads to better diagnosis of any eye condition. In this regard, since IOP is measured through analysis of the (dynamic) measured signal, rather than static deformation parameters (for example, such as applanation time), the tonometer also facilitates repeatable and automated non-contact IOP measurement. Notably, the tonometer enhances the precision and automation of IOP measurement itself. This configuration of the tonometer simplifies alignment of the displacement sensor with the exit interface of the air pulse generator, reduces error, ensures comfort of the user, streamlines a design of the tonometer, and provides accurate and reliable measurements of the deformations. Hence, this makes the tonometer user-friendly, and simple.

[0027] In a second aspect, the present disclosure provides a method for measuring intraocular pressure of an eye with a tonometer, the method comprising:

[0028] - aligning the tonometer with respect to the eye;

[0029] - providing an excitation air pulse towards the eye along a principal axis of measurement of the tonometer;

[0030] - measuring a signal related to deformations of the eye caused by the provided air impulse;

[0031] - determining the intraocular pressure of the eye from the measured signal.

[0032] The present disclosure provides the aforementioned second aspect to measure the (IOP) of the eye without making any direct contact with the eye, and from a same point where the excitation air pulse is incident on the eye. Herein, the tonometer is aligned correctly relative to the eye to minimize any spatial discrepancy that could prevent determining the intraocular pressure in an accurate manner. Moreover, due to a co-centric arrangement of constituents of the tonometer, measuring the signals related to the deformations are from the same point where the excitation air pulse is sent towards the eye eliminates errors due to spatial misalignment. In this regard, providing the excitation air pulse towards the eye in a co-centric manner with the tonometer, along the principal axis of measurement of the tonometer, prevents such spatial misalignment. In this way, accurate and reliable measurements of the deformations are measured, which resultantly provides accurate IOP, which leads to better diagnosis of any eye condition when compared to conventional tonometers. In particular, the measured signal is indicative of the cornea's biomechanical response, and using the measured signal to determine the IOP allows for improving measurement accuracy and reliability of the IOP. Moreover, the method provides high measurement repeatability. Thus, measuring the intraocular pressure of the eye using the method facilitates a user-friendly, simple, and effective solution for IOP measurement.

[0033] Throughout the present disclosure, the term "tonometer" refers to a device that is used to measure the intraocular pressure (IOP) of the eye. Throughout the present disclosure, the term "air pulse generator" refers to a component of the tonometer for producing the excitation air pulse which is directed onto a corneal surface of the eye when measuring the IOP. Herein, the excitation air pulse is a pulse of compressed air. The air exit element is designed to discharge the excitation air pulse from the air pulse generator via the exit interface. Herein, the exit interface of the air exit element directs a flow of the excitation air pulse.

[0034] Optionally, the air pulse generator comprises a pressure chamber, a pressure generation means configured to generate a pressure inside pressure chamber, and a controllable valve configured to release air from the exit interface. Herein, the pressure chamber is an enclosure within the air pulse generator where compressed air is stored before being released. The pressure chamber is designed to maintain a consistent level of air pressure. The pressure generation means is configured to generate the excitation air pulse at a specific pressure level within the pressure chamber, which can be controlled and adjusted based on requirement. Examples of the pressure generation means may include, but are not limited to, a reciprocating air compressor, a rotary screw air compressor, and a centrifugal air compressor. Moreover, the controllable valve is configured to open and close to release air within the air pulse generator as the excitation air pulse. The controllable valve can be controlled in a precise and a swift manner for release of the excitation air pulse. Examples of the controllable valve may include, but are not limited to, a solenoid valve, a diaphragm valve, a check valve, a pressure relief valve, and a control valve.

[0035] Throughout the present disclosure, the term "displacement sensor" refers to a device that measures a response of the corneal surface of the eye to the excitation air pulse. Herein, the response is at least one of: a change in position of the corneal surface of the eye relative to a reference point, an oscillation frequency of the corneal surface, an extent of deformations, recovery from said deformations. The displacement sensor is configured to collect sensor data when the tonometer is in use, and the excitation air pulse is applied on the corneal surface of the eye. This sensor data is sent to the controller. The controller is then configured to process the sensor data to measure the deformation of the eye. In this regard, the excitation air pulse causes the corneal surface to oscillate in resonance frequency of said excitation air pulse. Such oscillations (namely, corneal oscillations) introduce deformations (for example, such as flattening of the corneal surface) of the eye for as long as the excitation air pulse impacts the corneal surface. Such deformations are then measured using the displacement sensor. The displacement sensor is configured to determine various characteristics of the oscillations observed on the corneal surface after the excitation air pulse impacts on the corneal surface. The deformations of the eye are necessary for assessing intraocular pressure and biomechanical properties of the eye, for example, such as, elasticity, stiffness, a response of the corneal surface to pressure with which the excitation air pulse is released from the exit interface of the air exit element, and similar. Such measurements of the deformations of the eye are then used to diagnose eye conditions that the user may be suffering from. Examples of the eye conditions may include, but are not limited to, glaucoma, keratoconus, and corneal abnormality. Examples of the various characteristics of the corneal oscillations may include, but are not limited to, an amplitude, a frequency, a damping factor, a duration, a phase, and a value corresponding to peak-to-peak amplitude, of the corneal oscillations. Herein, the various characteristics of the corneal oscillations could be dependent on a force of the excitation air pulse exerted on the corneal surface.

[0036] Throughout the present disclosure, the term "principal axis of measurement" refers to a primary line along which the displacement sensor is arranged to measure the deformations of the eye. Hence, the displacement sensor is configured to determine changes in position of the corneal surface of the eye along the principal axis of measurement. A technical effect of the aforementioned feature is that minute changes in position of the corneal surface is determined in a consistent and reproducible manner, thus providing reliable measurements of the deformations of the eye. For example, the principal axis of measurement may be a straight line passing centrally through the displacement sensor.

[0037] Throughout the present disclosure, the term "exit interface" refers to a point from where the excitation air pulse exits the air pulse generator. The exit interface is aligned in such a manner that the excitation air pulse exits along the principal axis of measurement of the displacement sensor. This alignment ensures that the measurement of the deformations by the displacement sensor is done from a same place where the excitation air pulse hits the corneal surface of the eye. In case the excitation air pulse is sent from a direction which is different from where the measurement of the deformations is taken, then there may be inaccuracies while determining the IOP. Such inaccuracies occur because the deformations of the eye may vary across different locations, thus providing inconsistent IOP with every measurement. Hence, aligning the exit interface along the principal axis of measurement improves accuracy and reliability of the measurement of deformations by ensuring that the deformations are along a same axis as the principal axis of measurement, thus minimizing measurement errors due to misalignment.

[0038] Optionally, the air exit element of the air pulse generator is implemented as an air pulse transfer pipe that extends between a pressure chamber of the air pulse generator and the principal axis of measurement of the displacement sensor. Herein, the "air pulse transfer pipe" refers to a conduit that carries pressurized air from the pressure chamber to the exit interface which is along the principal axis of measurement. In this regard, the air pulse transfer pipe is designed to direct the excitation air pulse from the air pulse generator to the corneal surface of the eye, along the principal axis of measurement. This is used to ensure that the excitation air pulse is provided at a same area where the deformations of the eye are measured by the displacement sensor. A technical effect of implementing the air exit element as the air pulse transfer pipe is that it facilitates consistent alignment of the excitation air pulse with the principal axis of measurement, which reduces a likelihood of any error while measuring the deformations.

[0039] Optionally, the displacement sensor has an aperture therein to accommodate the exit interface of the air exit element. Herein, the term "aperture" refers to an opening within a structure of the displacement sensor. In this regard, dimensions of the aperture are such that it ensures that the air exit element is integrated with the displacement sensor, along the principal axis of measurement. Such configuration of the tonometer ensures that the excitation air pulse is delivered along the principal axis of measurement of the displacement sensor. A technical effect of the displacement sensor having the aperture therein is that it allows for a compact and integrated design of the tonometer, which is beneficial when space is limited. Another technical effect of the displacement sensor having the aperture therein is that it reduces chances of misalignment between the excitation air pulse and the principal axis of measurement, thereby enhancing accuracy of measuring the deformations of the eye.

[0040] Optionally, the displacement sensor is one of: a high-resolution camera, a confocal chromatic sensor, an ultrasonic sensor, a laser interferometer. When the displacement sensor is implemented as the high-resolution camera, the sensor data is in a form of images of the user's eyes. When the displacement sensor is implemented as the confocal chromatic sensor, the sensor data is in form of depth measurements corresponding to different wavelengths of reflected light at different points on the corneal surface of the eye. When the displacement sensor is implemented as the ultrasonic sensor, the sensor data is in a form of Time-of-Flight measurements for reflected ultrasonic waves. When the displacement sensor is implemented as the laser interferometer, the sensor data is in a form of phase shift data corresponding to the deformation of the eye. A technical effect of the aforementioned feature is that the displacement sensor is selected from sensors that are cost effective and easy to implement, as per requirement. Another technical effect of the aforementioned feature is that it facilitates precise and reliable measurement of the deformations, as such sensors provide high- resolution, real time (or near-real time) sensor data. Such sensor data enables determination of the IOP accurately.

[0041] Optionally, the confocal chromatic sensor comprises:

[0042] - an optical arrangement having an aperture therein to accommodate the exit interface of the air exit element; - a light source; and

[0043] - a light detector, wherein the light source emits light towards the optical arrangement wherefrom the light is transmitted towards the eye, and wherein reflections of the light from the eye pass through the optical arrangement and are received at the light detector.

[0044] In this regard, the term "optical arrangement" refers to an arrangement of optical components that are aligned and configured in such a manner that the light is focussed, directed, and / or manipulated for measuring the deformations of the eye. Optionally, the optical arrangement comprises at least one of: at least one lens, a beam splitter, a reflective mirror, a semi-reflective mirror, that is configured to focus the light on the corneal surface of the eye. Moreover, when the exit interface of the air exit element is accommodated in the aperture, such arrangement allows the excitation air pulse to be directed towards the eye without interfering with an optical path of the light emitted by the light source. Herein, the term "light source" refers to an element from which the light emanates, wherein this light is polychromatic light (for example, such as white light). In this regard, polychromatic light is a combination of different wavelengths of light, which is utilised when measuring the signal related to the deformations, using the displacement sensor.

[0045] Optionally, the light source comprises a visible-light emitting diode. Optionally, the light source is implemented as any one of: an active light source, a passive light source. When the light source is implemented as the active light source, it means that the light source provides the light by emitting the light itself. When the light source is implemented as the passive light source, it means that the light source provides the light by reflecting the light incident thereupon. Advantageously, implementing the light source in such a manner provides flexibility when the tonometer is used in various environmental conditions. Subsequently, the light emitted by the light source passes through the optical arrangement, wherein the light is divided into its constituent colours i.e., red colour, green colour, blue colour etc. Herein, each constituent colour of light has a particular wavelength, and such different wavelengths of light are focused at different distances along the principal axis of measurement, due to dispersion when the light passes through the optical arrangement. In this regard, only light of a particular wavelength is focussed properly on the corneal surface, while light of other wavelengths may not be focussed on the corneal surface. For example, a light of red colour may be focussed behind the corneal surface, a light of green colour may be focussed on the corneal surface, and a light of blue colour may be focussed in front of the corneal surface.

[0046] Thereafter, the light detector converts the reflected light into the signals that is measured to determine the deformations of the eye. The light detector is configured to analyse the particular wavelength that is reflected from the corneal surface, to determine a distance to the corneal surface, as each wavelength corresponds to a specific distance.

[0047] As an example, the confocal chromatic sensor may be used to determine a distance between said confocal chromatic sensor and the corneal surface of the eye. In this regard, at least one wavelength of the light reflected from the corneal surface of the eye may be analysed to determine the distance. As another example, principle of confocal chromatic sensor may be used for a confocal microscope. In this regard, the confocal microscope may use a detector to image samples of the corneal surface of the eye, to determine a distribution of light intensity across different depths of the corneal surface of the eye. This information may then be used to visualize a structure of the samples of the corneal surface of the eye.

[0048] 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 is configured to control the air pulse generator by adjusting the excitation air pulse directed towards the eye of the person, to accurately measure the IOP of the eye. In an example, 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 configured to receive input from the displacement sensor pertaining to the deformations of the eye; to process information available in the received input; and to determine the IOP of the eye. The controller may be implemented as an internal component of the tonometer, an external component of the tonometer, or a combination thereof.

[0049] The controller is configured to generate control signals to generate the excitation air pulse, wherein the control signals could comprise at least one parameter of generating the excitation air pulse. Optionally, the at least one parameter comprises at least one of: a pressure, a duration, a timing, of generating the excitation air pulse. Advantageously, utilizing the at least one parameter for generating the excitation air pulse, allows for fine-tuning the excitation air pulse according to requirements of the eye, which enhances a flexibility and precision of determining the IOP. In this regard, the pressure is adjusted to ensure that the excitation air pulse is neither too strong nor too weak, thus reducing a risk of inaccurate determination of the IOP due to inappropriate force (as pressure is directly related to force). Moreover, the duration and / or the timing of generating the excitation air pulse is adjusted to ensure that the excitation air pulse is delivered at a moment when it is required to capture a corneal response, thus improving reliability in determining the IOP.

[0050] Upon receiving the control signals from the controller, the air pulse generator adjusts its constituents (for example, the pressure generating means, the controllable valve, etc.) to generate the excitation air pulse based on the at least one parameter. The excitation air pulse is then directed through the air exit element and impacts the corneal surface of the eye, via the exit interface. This excitation air pulse then introduces the deformations, i.e., physical changes on the corneal surface of the eye, wherein such deformations are specific and controllable (due to optionally generating the excitation air pulse by utilizing the at least one parameter). As discussed above, measuring the deformations of the eye are used to determine the eye condition that the user may be suffering from.

[0051] Optionally, the excitation air pulse is a short air pulse or a long air pulse. When the excitation air pulse is the short air pulse, it means that brief bursts of the excitation air pulse are released from the air exit element. Such short air pulses provide a rapid impact and / or a transient impact on the corneal surface of the eye. When the excitation air pulse is the long air pulse, it means that sustained bursts of the excitation air pulse are released from the air exit element. Such long air pulse provides a sustained effect on the corneal surface of the eye, i.e., the excitation air pulse impacts the eye for a longer time than the short air pulse. A technical effect of different types of the excitation air pulse facilitates for tailored measurements of deformations of the eye, thus enhancing the accuracy and versatility in assessing the IOP of the eye under various conditions.

[0052] In an embodiment, the displacement sensor measures the signal related to the deformations of the eye caused by the short air pulse, for a first duration of time ranging from 1 millisecond (msec)-lO msec. In this regard, the deformations that are rapid and minute are accurately captured within a short time frame. The measurement of such signal provides real-time information on immediate response of the eye to the excitation air pulse, thus facilitating immediate analysis and interpretation. Hence, there is high-speed sampling, which involves highspeed data acquisition to capture rapid changes of the eye accurately. In the first duration of time, initial response of the eye to the excitation air pulse is captured. The first duration of time may, for example, lie in a range of 1, 2, 4, or 7 msec to 3, 7, 9, or 10 msec. A technical effect of the aforementioned feature is that it limits measurement of the signal by the displacement sensor to a time period that is most relevant, thus minimizing an amount of air required to be generated by the air pulse generator while delivering effective results.

[0053] In another embodiment, the displacement sensor measures the signal related to the deformations of the eye caused by the long air pulse, for a second duration of time ranging from 10 msec-100 msec. In this regard, the displacement sensor detects and monitors deformations on the corneal surface caused by the excitation air pulse which is sustained in nature. The measurement of such signal allows capturing both the immediate response of the eye and an evolving deformation response of the eye. Hence, there is continuous sampling to accurately capture progressive changes within the second duration of time, wherein the signal represents dynamic changes of the eye. In the second duration of time, an evolution and stabilization of the deformation of the eye is captured. The second duration of time may, for example, lie in a range of, 10, 12, 15, 20, 30, 50, 65 or 95 msec to 15, 40, 60, 80, 90, 95, 98, or 100 msec. A technical effect of the aforementioned feature is that it provides information on a process of the deformation over the second duration of time, thus facilitating a deeper and detailed understanding of the response of the eye upon impact of the excitation air pulse. Such deeper and detailed understanding is due to the continuous sampling of the progressive changes when the excitation air pulse is incident on the eye.

[0054] The controller is configured to continuously or periodically collect the sensor data when the eye is being deformed upon impact from the excitation air pulse. Such sensor data is collected by the controller in real time or near-real time. When the eye deforms in response to the excitation air pulse, the displacement sensor collects sensor data related to it and generates corresponding signals that represents the deformations. Such signals are received by the controller, and are processed by the controller to determine at least one of: an extent of the deformation, a rate of change of the deformation, a timing of the deformations relative to the impact of the excitation air pulse on the corneal surface.

[0055] In an instance, when the displacement sensor is implemented as the high-resolution camera, the high-resolution camera generates corresponding signals related to the deformations of the eye. The high- resolution camera captures images of the corneal surface before, during, and after the excitation air pulse is applied, and corresponding signals are measured by configuring the controller.

[0056] In another instance, when the displacement sensor is implemented as the confocal chromatic sensor, the confocal chromatic sensor generates corresponding signals related to the deformations of the eye. The confocal chromatic sensor measures the signal by emitting a broadspectrum light beam towards the eye and analysing the reflected light to determine distances to the corneal surface.

[0057] In yet another instance, when the displacement sensor is implemented as the ultrasonic sensor, the ultrasonic sensor generates corresponding signals related to the deformations of the eye. The ultrasonic sensor measures the signal by emitting ultrasonic waves towards the eye and analysing reflected echoes to determine distances to the corneal surface.

[0058] In still yet another instance, when the displacement sensor is implemented as the laser interferometer, the laser interferometer generates corresponding signals related to the deformations of the eye. The laser interferometer measures the signal by analysing interference patterns created by laser beams reflected from the cornea and a reference manner. The laser interferometer then calculates distances to the corneal surface.

[0059] The controller is configured to calculate the IOP based on the deformations of the eye. The measured signal is pre-processed to extract features of the measured signal, which can be used to determine the IOP. Optionally, the controller is further configured to apply any one of: an algorithm, a model, to correlate the features with the IOP. Optionally, any one of: the algorithm, the model, user reference data, is used to accurately relate the measured signal to a value of the IOP. Such reference data could be historical data related to the deformations of the eye. A technical effect of calculating the IOP in such a manner is that it facilitates determination of the eye condition for different users in a customised manner based on characteristics of an individual user, accuracy while diagnosing the eye condition of the individual user, and treatment required.

[0060] Optionally, when determining the intraocular pressure of the eye, the controller is configured to:

[0061] - determine, from the measured signal, an oscillation frequency of corneal oscillations; and

[0062] - calculate, from the oscillation frequency, a value of the intraocular pressure.

[0063] Herein, the term "oscillation frequency" refers to a frequency at which the corneal surface oscillates after being deformed by the excitation air pulse. In this regard, the oscillation frequency is directly related to a response of the eye to the excitation air pulse. Optionally, the controller is configured to employ algorithms to determine the oscillation frequency. Such algorithms are frequency domain analysis methods, for example, such as Fast Fourier Transform, and are well-known in the art. By configuring the controller to determine the oscillation frequency from the measured signal, the tonometer captures a robust physical parameter that has a direct relationship with IOP based on fundamental biomechanical principles. The (stable) oscillation frequency is used as a biomechanical indicator to compute the IOP precisely, in real-time. The controller is configured to apply a predefined correlation algorithm or a predefined correlation model that correlates the oscillation frequency with the values of the intraocular pressure. The controller is configured to use the oscillation frequency, and the predefined correlation algorithm or the predefined correlation model, to calculate the value of the intraocular pressure. A technical effect of calculating the value of the intraocular pressure in such a manner is that it makes the calculations less error- prone as such calculation leverages mechanical response of the corneal surface, as the intraocular pressure directly influences said mechanical response. In other words, the IOP is determined accurately and reliably through analysis of the oscillation frequency. Herein, a high IOP leads to a low deformation when the excitation air pulse is applied, while a low IOP results in high deformation. By measuring the oscillation frequency of the corneal oscillations from the measurement signal, the controller can derive the intraocular pressure through a direct physical relationship by leveraging the aforesaid parameter rather than relying on other deformation parameters that are prone to individual variations in corneal properties (for example, such as applanation time or deformation amplitude). This approach eliminates the need for calibration against reference tonometers, reduces measurement variability caused by individual corneal biomechanical properties, and provides a reliable, more consistent correlation between the measured signal and actual intraocular pressure. Furthermore, utilizing frequency analysis (of the oscillation frequency) rather than amplitude or time-based measurements potentially increases measurement accuracy across different patient populations and corneal conditions, thereby enhancing the clinical reliability and diagnostic value of the tonometer while simplifying the overall IOP measurement process. In other words, this frequency-based approach circumvents the traditional challenges associated with corneal biomechanical variability by focusing on oscillatory behaviour that more consistently correlates with the eye's internal pressure across different patient populations.

[0064] According to an alternative embodiment the air pulse generator of the tonometer is configured to provide a frequency sweep of excitation air pulses, the deformation sensor is configured to measure a signal related to deformations associated with excitation air pulses of each frequency of the frequency sweep, the controller is configured to select a frequency value of the frequency sweep corresponding to largest deformation, wherein the selected frequency value is used to determine value of the intraocular pressure. In this regards the frequency sweep refers on providing series of excitation air pulses first, say with frequency of 200Hz and then increasing pulse frequency from 200Hz to 500Hz. As an example, the pulse frequency may be from 200, 250, 300, 350, 400, 450 or 475Hz up to 225, 275, 325, 375, 425, 475 or 500Hz. The increase can be done, as an example with steps of 1Hz, 2Hz, 5Hz, 10Hz or 20Hz. This can be done for example by controlling (oscillating) speed of piston movement if the air pulses are generated with a piston. If the air pulses are generated by opening and closing a valve the closing and opening of valve would take place with said frequency. This way different frequency air pulses (or air waves) impact corneal surface causing it to deform. When the frequency is same as resonant frequency of the eye the deformations will be largest. This resonant frequency correlates with intraocular pressure of the eye. In other words when a frequency of air pulses which cause the maximum deformation is found we can determine IOP using that. IOP vs resonant frequency can be obtained from look up table. Optionally, the controller is configured to generate this look up table by executing a calibration process.

[0065] A technical effect of leveraging the frequency value that yields the largest deformation for IOP measurement is that it enhances sensitivity and accuracy of the IOP measurement, as it is based on maximally responsive biomechanical behaviour of the cornea. Moreover, this frequency sweepbased approach is also inherently less affected by patient-specific variations, thus enabling consistently reliable IOP measurement across diverse patient populations.

[0066] The present disclosure also relates to the second aspect as described above. Various embodiments and variants disclosed above, with respect to the aforementioned first aspect, apply mutatis mutandis to the second aspect.

[0067] The step of aligning the tonometer with respect to the eye is important as it enables safe operation of the tonometer for obtaining accurate measurements of the intraocular pressure of the eye. 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.

[0068] Optionally, the measured signal is an oscillation frequency of a cornea of the eye.

[0069] A technical effect of the aforementioned feature is that is enhances an accuracy and reliability when calculating the IOP, as the oscillation frequency is directly influenced by an internal pressure of the eye.

[0070] Optionally, the method further comprises calculating, from the oscillation frequency of the cornea of the eye, a value of the intraocular pressure of the eye.

[0071] A technical effect of calculating the value of the intraocular pressure in such a manner is that it makes the calculations less error-prone as such calculation leverages mechanical response of the corneal surface, as the intraocular pressure directly influences said mechanical response. Herein, a high IOP leads to a low deformation when the excitation air pulse is applied, while a low IOP results in high deformation.

[0072] According to one embodiment the excitation air pulse is provided as a set of air pulses over frequency sweep and a frequency associated with maximum deformations is used to determine intra ocular pressure of an eye. The frequency sweep "scans" over different frequencies (of pressure change at corneal surface) to find resonant frequency of the cornea. This corresponds to largest deformation. The resonant frequency can be used to determine intra ocular pressure of the eye. The IOP thus determined is accurate and reliable. Furthermore, this frequency sweep-based approach is also enables consistently reliable IOP measurement across diverse patient populations.

[0073] DETAILED DESCRIPTION OF THE DRAWINGS

[0074] Referring to FIG. 1, illustrated is a schematic illustration of a tonometer 100, in accordance with an embodiment of the present disclosure. The tonometer 100 comprises an air pulse generator 102 having an air exit element 104, a displacement sensor 106 for measuring deformations of an eye 108, and a controller 110. The displacement sensor 106 has a principal axis 112 of measurement (as shown by dashed line), wherein an exit interface 114 of the air exit element 104 is arranged along the principal axis 112 of measurement. The controller 110 is communicably coupled to the air pulse generator 102 and the displacement sensor 106. The controller 110 is configured to control the air pulse generator 102 to generate an excitation air pulse 116 and control the air pulse generator 102 to send the excitation air pulse 116 towards the eye 108 via the exit interface 114 of the air pulse generator 102, for producing the deformations; measure a signal related to the deformations, using the displacement sensor 106; and determine the intraocular pressure of the eye 108 from the measured signal.

[0075] Optionally, the displacement sensor 106 has an aperture 118 therein to accommodate the exit interface 114 of the air exit element 104. Optionally, the air exit element 104 of the air pulse generator 102 is implemented as an air pulse transfer pipe that extends between a pressure chamber 120 of the air pulse generator 102 and the principal axis 112 of measurement of the displacement sensor 106.

[0076] FIG. 1 is merely an example, which should not unduly limit the scope of the claims herein. A person skilled in the art will recognize many variations, alternatives, and modifications of embodiments of the present disclosure.

[0077] Referring to FIG. 2, illustrated is an exemplary schematic illustration of a tonometer 200, in accordance with an embodiment of the present disclosure. Herein, the tonometer 200 comprises an air pulse generator 202 having an air exit element 204, a displacement sensor (depicted as a confocal chromatic sensor 206 that is shown by a dotted box) for measuring deformations of an eye 208, and a controller 210. The confocal chromatic sensor 206 has a principal axis 212 of measurement, wherein an exit interface 214 of the air element 204 is arranged along the principal axis 212 of measurement. The controller 210 is communicably coupled with the air pulse generator 204 and the confocal chromatic sensor 206. The confocal chromatic sensor 206 comprises an optical arrangement (depicted as a lens 216 and a beam splitter 218) having an aperture 220 therein to accommodate the exit interface 214 of the air exit element 204, a light source 222, and a light detector 224. When the tonometer 200 is in use, the light source 222 emits light 226 towards the lens 216 and beam splitter 218 wherefrom the light 226 is transmitted towards the eye 208. Herein, the beam splitter 218 may change a direction of the light 226 to be incident on the lens 216. The light 226 passes through the lens 216, wherein said light 226 disperses into its constituent colours (namely, light of red colour as shown by a long dashed line 228A, light of green colour as shown by a dashed line 230A, and light of blue colour as shown by a square dotted line 232A) of different wavelengths that are focussed at different points (as shown by points P, P’ and P") on cornea 234 of the eye 208, along the principal axis 212 of measurement of the confocal chromatic sensor 206. In this regard, the point P is formed in front of the cornea 234, the point P' is formed on the cornea 234, and the point P" is formed behind the cornea 234. Subsequently, the constituent colours are reflected, i.e., reflected light of red colour as shown by the long-dashed line 228B, reflected light of green colour as shown by the dashed line 230B, and reflected light of blue colour as shown by the square dotted line 232B. The reflected light of green colour 230B, that is reflected from point P' from the eye 208, passes through the optical arrangement and is received at the light detector 224. This reflected light of green colour 230B is determined to be a distance of the eye 208 when excitation air pulse 236 hits the eye 208, as this wavelength of light is focussed on the cornea 234 of the eye 208.

[0078] FIG. 2 is merely an example, which should not unduly limit the scope of the claims herein. A person skilled in the art will recognize many variations, alternatives, and modifications of embodiments of the present disclosure.

[0079] Referring to FIG. 3A, illustrated is an exemplary schematic diagram of an implementation of a tonometer 300 for measuring an intraocular pressure value of an eye 302, in accordance with an embodiment of the present disclosure. As shown, an excitation air pulse 304 is sent towards the eye 302 which results in corneal oscillation 306, depicted as a signal 308 related to the corneal oscillations 306. Herein, the signal 308 represents a curve of resonance frequency. A displacement sensor 310 measures the signal 308 for determining a value of the intraocular pressure value.

[0080] Referring to FIG. 3B, illustrated is a graphical representation of an intraocular pressure value as a function of corneal frequency, in accordance with an embodiment of the present disclosure. As shown, the intraocular pressure values are plotted on the X-axis against the corneal frequency on the Y-axis. As shown, with an increase in the corneal frequency, the intraocular pressure values also increase.

[0081] FIGs. 3A-3B are merely examples, which should not unduly limit the scope of the claims herein. A person skilled in the art will recognize many variations, alternatives, and modifications of embodiments of the present disclosure.

[0082] Referring to FIG. 4, illustrated are 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 402, the tonometer is aligned with respect to the eye. At step 404, an excitation air pulse is provided towards the eye along a principal axis of measurement of the tonometer. At step 406, a signal is measured that is related to deformations of the eye caused by the provided excitation air pulse. At step 408, the intraocular pressure of the eye is measured from the measured signal.

[0083] 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.

[0084] FIG. 5 is illustration of deformations associated with a frequency sweep of air pulses, in accordance with an embodiment of the present disclosure. In x-axis is frequency of air pulses (pressure changes). Y-axis is arbitrary units representing relative deformation. A clear peak of maximum deformation can be seen. Example of a deformation is how much cornea surface moves from its normal resting position inwards. The maximum deformation-related frequency is same as resonant frequency of the eye. This resonant frequency correlates with intraocular pressure of the eye.

Claims

CLAIMS1. A tonometer (100, 200, 300) for measuring intraocular pressure of an eye (108, 208, 302), the tonometer comprising- an air pulse generator (102, 202) having an air exit element (104, 204);- a displacement sensor (106, 310) for measuring deformations of the eye, wherein the displacement sensor has a principal axis of measurement, and wherein an exit interface (114, 214) of the air exit element is arranged along the principal axis (112, 212) of measurement; and- a controller (110, 210) communicably coupled to the air pulse generator and the displacement sensor, wherein the controller is configured to: control the air pulse generator to generate an excitation air pulse (116, 236, 304) and control the air pulse generator to send the excitation air pulse towards the eye via the exit interface of the air exit element, for producing the deformations; measure a signal (308) related to the deformations, using the displacement sensor; and determine the intraocular pressure of the eye from the measured signal.

2. A tonometer (100, 200, 300) according to claim 1, wherein the displacement sensor (106, 310) has an aperture (118, 220) therein to accommodate the exit interface (114, 214) of the air exit element (104, 204).

3. A tonometer (100, 200, 300) according to claim 1 or 2, wherein the displacement sensor (106, 310) is one of: a high-resolution camera, a confocal chromatic sensor (206), an ultrasonic sensor, a laser interferometer.

4. A tonometer (100, 200, 300) according to claim 3, wherein the confocal chromatic sensor (206) comprises:- an optical arrangement having an aperture (220) therein to accommodate the exit interface (214) of the air exit element (204);- a light source (222); and- a light detector (224), wherein the light source emits light (226) towards the optical arrangement wherefrom the light is transmitted towards the eye (108, 208, 302), and wherein reflections of the light from the eye pass through the optical arrangement and are received at the light detector.

5. A tonometer (100, 200, 300) according to any of the preceding claims, wherein the air exit element (104, 204) of the air pulse generator (102, 202) is implemented as an air pulse transfer pipe that extends between a pressure chamber (120) of the air pulse generator and the principal axis (112, 212) of measurement of the displacement sensor (106, 310).

6. A tonometer (100, 200, 300) according to any of the preceding claims, wherein the excitation air pulse (116, 236, 304) is short air pulse or a long air pulse.

7. A tonometer (100, 200, 300) according to claim 6, wherein the displacement sensor (106, 310) measures the signal (308) related to the deformations of the eye (108, 208, 302) caused by the short air pulse, for a first duration of time ranging from 1 millisecond (msec)-10 msec.

8. A tonometer (100, 200, 300) according to claim 6, wherein the displacement sensor (106, 310) measures the signal (308) related to the deformations of the eye (108, 208, 302) caused by the long air pulse, for a second duration of time ranging from 10 millisecond (msec)-lOO msec.

9. The tonometer (100, 200, 300) according to any of the preceding claims, wherein when determining the intraocular pressure of the eye (108, 208, 302), the controller (110, 210) is configured to:- determine, from the measured signal (308), an oscillation frequency of corneal oscillations (306); and- calculate, from the oscillation frequency, a value of the intraocular pressure.

10. The tonometer according to any of the preceding claims 1-5, wherein the air pulse generator is configured to provide a frequency sweep of excitation air pulses, the deformation sensor is configured to measure a signal related to deformations associated with excitation air pulses of each frequency of the frequency sweep, the controller is configured to select a frequency value of the frequency sweep corresponding to largest deformation, wherein the selected frequency value is used to determine value of the intraocular pressure.

11. A method for measuring intraocular pressure of an eye (108, 208, 302) with a tonometer (100, 200, 300), the method comprising:- aligning the tonometer with respect to the eye;- providing an excitation air pulse (116, 236, 304) towards the eye along a principal axis (112, 212) of measurement of the tonometer;- measuring a signal (308) related to deformations of the eye caused by the provided excitation air pulse (116, 236, 304); and- determining the intraocular pressure of the eye from the measured signal.

12. A method according to claim 11, wherein the measured signal (308) is an oscillation frequency of a cornea (234) of the eye (108, 208, 302).

13. A method according to claim 12, wherein the method further comprises calculating, from the oscillation frequency of the cornea (234) of the eye (108, 208, 302), a value of the intraocular pressure of the eye.

14. A method according to claim 11, wherein the excitation air pulse is provided as a set of air pulses over frequency sweep and a frequencyassociated with maximum deformations is used to determine intra ocular pressure of an eye.

Images