An air pulse based tonometer

Abstract

Disclosed is a tonometer (100, 200) for measuring an intraocular pressure value of an eye (104, 204). The tonometer comprising a a sensor setup an air pulse generator (110); a controller (112) communicatively coupled to the first sensor, the second sensor and the air pulse generator. The controller is configured to: measure a distance between the eye and the tonometer with the sensor setup; determine a first set of operational parameters of the air pulse generator based on the distance; control the air pulse generator to send a first excitation air pulse (114, 202) towards the eye; measure a first signal (206) related to corneal oscillations caused by the sent first excitation air pulse, with the sensor setup; and determine the intraocular pressure value from the measured first signal. Disclosed is a method for measuring the intraocular pressure value of the eye using the tonometer.

Description

AN AIR. PULSE BASED TONOMETER

[0002] TECHNICAL FIELD

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

[0006] BACKGROUND

[0008] The accurate measurement of intraocular pressure (IOP) is pivotal in ophthalmic diagnostics. A tonometer, such as air pulse tonometer, etc., may be used for measuring IOP of an eye of the examinee.

[0010] The air pulse tonometer is configured to impose an air pulse on the eye of the examinee to exert a certain force on corneal surface of the eye causing an oscillation thereof, and subsequently IOP value is determined, based on such corneal oscillations. Notably, a distance between the air pulse tonometer and the eye influences the force that is delivered to the cornea by the air pulse. Moreover, the force further influences an amplitude and a shape of the corneal oscillation signal which are essential for IOP measurement. Thus, adjustment of force of the air pulse with respect to the distance between the air pulse tonometer and the eye is an essential factor for accuracy in IOP measurement. However, the adjustment of force of the air pulse requires iterative calibration of the air pulse tonometer for: (1) proper alignment thereof with the eye of the examinee, (2) adjusting operational parameters thereof to exert a required force at the eye.

[0012] Therefore, in light of the foregoing discussion, there exists a need to overcome the aforementioned drawbacks. SUMMARY

[0014] The aim of the present disclosure is to provide a tonometer and a method to minimize iterative calibration of the tonometer to measure intraocular pressure (IOP) by adjusting various operational and functional parameters as a function of distance between the tonometer and an eye of the examinee. The aim of the present disclosure is achieved by a tonometer and a method for measuring an intraocular pressure value 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.

[0016] 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.

[0018] BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an illustration of a schematic diagram of a tonometer for measuring an intraocular pressure value of an eye, when in use, in accordance with an embodiment of the present disclosure;

[0020] FIG. 2A is an illustration of a 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;

[0022] FIG. 2B is an illustration of a graphical representation of an intraocular pressure value as a function of corneal frequency, in accordance with an embodiment of the present disclosure; and FIG. 3 is an illustration of a flowchart depicting steps of a method for measuring an intraocular pressure value of an eye, using the tonometer of FIG. 1, in accordance with an embodiment of the present disclosure. DETAILED DESCRIPTION OF EMBODIMENTS

[0024] 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.

[0026] In a first aspect, the present disclosure provides a tonometer for measuring an intraocular pressure value of an eye, the tonometer comprising

[0028] a sensor setup;

[0030] an air pulse generator; and

[0032] a controller communicatively coupled to the sensor setup and the air pulse generator, the controller configured to:

[0034] measure a distance between the eye and the tonometer with the sensor setup;

[0036] determine a first set of operational parameters of the air pulse generator based on the distance;

[0038] control the air pulse generator to send a first excitation air pulse towards the eye;

[0040] measure a first signal related to corneal oscillations caused by the sent first excitation air pulse, with the sensor setup; and determine the intraocular pressure value from the measured first signal. The disclosed tonometer provides an accurate calibration of various operational parameters of the air pulse generator to ensure that a desired force is exerted on the cornea of the eye, based on the automatic distance measurement between the tonometer and the eye. Beneficially, the calibration or adjustment reduces manual intervention during intraocular pressure (IOP) measurement and minimizes discomfort of a patient / examinee. Moreover, the aforementioned tonometer reduces the number of steps and time taken for IOP measurement, and enhances accuracy of IOP measurement.

[0042] In a second aspect, the present disclosure provides a method for measuring an intraocular pressure value of an eye, using a tonometer, the method comprising

[0044] measuring a distance between the eye and the tonometer; determining a first set of operational parameters of an air pulse generator based on the distance;

[0046] controlling the air pulse generator to send a first excitation air pulse towards the eye;

[0048] measuring a first signal related to corneal oscillations caused by the sent first excitation air pulse; and

[0050] determining the intraocular pressure value from the measured first signal.

[0052] The disclosed method allows effective measurement of IOP as a function of distance between the tonometer and the eye, and utilizing the measured distance to adjust various operational parameters of the tonometer, thereby reducing time consumption in iterative calibration of the tonometer for accurate IOP measurement.

[0054] Throughout the description, the term "tonometer" refers to a medical device used to measure the intralocular pressure (IOP) value of the eye. The term "IOP value" of the eye refers to a value of a fluid pressure inside the eye, exerted by the aqueous humor filling the anterior chamber of the eye as well as vitreous humour filling the posterior chamber of the eye. In an implementation, the tonometer is an air pulse tonometer. The tonometer comprises the sensor setup. The sensor setup can comprise a one physical sensor type which can measure both the distance and corneal oscillations in response to the air pulse. Alternatively, the sensor setup can comprise a first sensor for measuring the distance and a second sensor for measuring the corneal oscillations. In general the sensor setup is configured, independently on physical setup, to detect and determine various IOP value measuring parameters, such as the distance between the eye and the tonometer, a frequency and / or amplitude of the corneal oscillation, a force exerted on the cornea, and so on. Beneficially, the sensor setup enables precise and reliable detection of both the distance between the tonometer and the eye, and the corneal response to the air pulse, essential for accurate, repeatable IOP readings and reduced risk of user error.

[0056] According to an embodiment the sensor setup comprises at least one of:

[0058] a first confocal chromatic sensor for measuring the distance and the corneal oscillations, or

[0060] a first confocal chromatic sensor for measuring the distance and a second confocal chromatic sensor for measuring the corneal oscillations. Benefit of using one physical sensor (the first confocal chromatic sensor) for measuring both the distance and the corneal oscillations is that one sensor is sufficient. This reduces the number of components, leading to a more compact, lightweight, and cost-effective device or tonometer. Moreover, with only one physical sensor, there is no risk of misalignment between separate distance and oscillation sensors, improving measurement reliability. Furthermore, only one physical sensor requires simpler calibration procedures and lower maintenance requirements, reducing setup as well as maintenance time and potential for user error. Additionally, only one physical sensor typically consumes less power, which is advantageous for portable or battery-operated devices.

[0062] Benefit of using a first confocal chromatic sensor for measuring the distance and a second confocal chromatic sensor for measuring the corneal oscillations is that sensor placements in the tonometer can be arranged in a way that the first confocal chromatic sensor is dedicatedly directed in an optimum way for distance measurement and the second dedicated for measuring the oscillations. This way each sensor can be optimized (e.g., in terms of wavelength range, sensitivity, orientation) for its specific measurement task, enhancing overall accuracy and performance, by reducing risk of cross-talk or interference between distance and oscillation signals.

[0064] According to alternative embodiment, the sensor setup comprises a distance sensor and a displacement sensor, in which the sensors are separate sensors.

[0066] In this regard, the distance sensor is a sensor that is configured to measure the distance between the eye and the tonometer. Specifically, the distance sensor measures the distance between the cornea of the eye and the tonometer. The distance sensor is configured to determine the distance by sending out a stimulus towards the cornea and analysing a response to the stimulus. The term stimulus used herein pertains to at least one of an ultrasonic stimulus, an infrared stimulus, a light pulse, a LASER, pulse, an electromagnetic stimulus. The response corresponding to the stimulus is analysed and the distance between the cornea and the tonometer is measured. A confocal chromatic sensor can be used to measure distance. In that regards, the first confocal chromatic sensor can be considered to be a distance sensor. Additionally, a camera can be used to measure distance i.e. camera is one example of a distance sensor. Moreover, the displacement sensor is configured to detect and measure a signal, namely the first signal, related to the change in cornea, namely corneal oscillations, during IOP value measurement. The term "first signal" as used herein refers to a signal containing information related to the various characteristics of the corneal oscillations caused by the impact from the first excitation air pulse. The displacement sensor is configured to utilize at least one of a plurality of detection techniques, such as confocal chromatic sensor, confocal microscopy, chromatic aberration, optical coherence tomography (OCT), camera or ultrasound, to capture and analyse the change in corneal surface. Since the displacement sensor measures displacements of the cornea as function of time it is a corneal oscillation sensor.

[0068] Beneficially, the dedicated distance sensor and the dedicated displacement sensor provide a modular and potentially more accurate approach, enhancing the tonometer's adaptability and performance in diverse clinical scenarios. Specifically, separating distance and displacement measurement allows each sensor to be optimized for its specific function, improving overall measurement fidelity. Moreover, the dedicated sensors minimize interference between distance and oscillation measurements, leading to clearer, more reliable signals.

[0070] Optionally, the sensor setup comprises a first sensor which is a distance sensor and a second sensor which is a displacement sensor. An example of the displacement sensor is a confocal chromatic sensor. An example of distance sensor is a confocal chromatic sensor or an ultrasound sensor. In this regard, optionally, the tonometer utilizes the first sensor to measure the distance of the tonometer from the cornea of the eye for proper alignment of the tonometer with the eye prior to IOP value measurement. Moreover, proper alignment of the tonometer with the eye allows suitable modification of the first set of operational parameters, i.e., various physical and functional attributes, of the tonometer based on the distance between the tonometer and the eye. Thereby, achieving the technical effect of accurate IOP value measurement. Additionally, the distance sensor allows minimizing the time taken for manual alignment and calibration of the tonometer, based on the measured distance between the eye and the tonometer. Moreover, the displacement sensor is used to detect the change in the cornea relative to an initial (or starting) position of the cornea, by measuring the first signal related to the corneal oscillations, as result of the first excitation air pulse incident thereon. The initial position of the cornea refers to a position of the cornea when the tonometer is aligned suitably with respect to an axis of the eye, prior to the measurement of the first signal. A technical effect achieved by utilization of the distance sensor and the displacement sensor is that iterative alignment and calibration of tonometer for accurate IOP measurement is reduced.

[0072] Optionally, the distance sensor is a camera or a first confocal chromatic sensor, and the displacement sensor is the first confocal chromatic sensor or a second confocal chromatic sensor. In this regard, the tonometer utilizes the camera or the first confocal chromatic sensor, to send the stimulus such as a light pulse which is reflected from the cornea of the eye. In an example, in a confocal chromatic sensor broad wavelengths of light are sent towards the cornea. Reflected light has peaks on wavelengths which represent distance (and displacement) of cornea. In another example, the camera can be utilized for measuring the distance between the tonometer and the eye by utilizing a stereoscopic effect to capture multiple images of the eye. In this regard, the distance between the eye and the tonometer is calculated based on any disparity in position between the corresponding points in the multiple images.

[0074] Moreover, the tonometer utilizes the first confocal chromatic sensor or the second confocal chromatic sensor to measure the first signal corresponding to the corneal oscillation for IOP value measurement. Optionally, the first sensor and the second sensor may be a single sensor, namely, the first confocal chromatic sensor, which can be used to determine both the distance of the tonometer from the cornea / eye as well as the displacement of the cornea, namely, corneal oscillation, thereby, beneficially, reducing constructional complexity.

[0076] Alternatively, optionally, the first sensor (distance sensor) and the second sensor (displacement sensor for measuring corneal oscillations) are different. For example, the first sensor is the camera and the second sensor is the second confocal chromatic sensor. In another example, the first sensor is the first confocal chromatic sensor and the second sensor is the second confocal chromatic sensor. It may be appreciated that when the first sensor and the second sensor are different, the said sensors may be arranged adjacent to each other along a common axis, parallel (opposite) or angularly along different axes thereof. A technical advantage of using the different first and second sensors is a higher degree of calibration for each type of IOP value measuring parameters. The first confocal chromatic sensor and the second confocal chromatic sensor typically emit a light pulse, such as a white light pulse. Said white light pulse when passes through an optical arrangement undergoes a chromatic aberration. The chromatic aberration of the white light pulse causes different wavelengths of light to focus at different distances on the cornea of the eye, along an optical axis aligned with the eye such that each wavelength corresponds to a specific focal plane on the cornea of the eye. Thereby, covering a large area of the cornea for accurate measurement of the change in cornea, namely corneal oscillation, by using the corresponding first signal, during IOP value measurement. Moreover, the tonometer comprises the air pulse generator which is configured to generate the first excitation air pulse that is directed towards the cornea for measurement of IOP value. Herein, the term "first excitation air pulse" refers to a controlled burst of air directed towards the eye at a first time instant, which can exert certain force on the corneal surface of the eye. The force exerted by the first excitation air pulse causes deformation or displacement in the cornea which is measured in the form of the first signal by the second sensor for measuring IOP value. Beneficially, the air pulse generator provides a non-contact, hygienic, and patient-friendly means of deforming the cornea for IOP measurement. The air pulse generator can be precisely controlled to deliver consistent force, improving measurement accuracy and patient comfort compared to contact-based methods.

[0078] Optionally, the air pulse generator comprises a pressure chamber, a control valve and a nozzle having an exit aperture. The pressure chamber comprises an air compressor configured to generate the first excitation air pulse. The air compressor may be at least one of: a reciprocating air compressor, a rotary screw air compressor, a centrifugal air compressor, and any suitable pressure generation means. The control valve is configured to regulate release of the first excitation air pulse generated in the pressure chamber. The control valve is at least one of: a solenoid valve, a diaphragm valve, a check valve, a pressure relief valve, and any such suitable valves which are capable of swift opening and closing. The nozzle comprises a first end coupled with the pressure chamber and a second end having the exit aperture. Optionally, the nozzle is designed in a manner where the first end has a wider diameter than the second end. Optionally, the diameter of the second end having the exit aperture is adjustable. The nozzle is configured to send the first excitation air pulse generated in the pressure chamber in a controlled manner via the exit aperture. In this regard, when the tonometer is aligned with the cornea, the first excitation air pulse is directed from the exit aperture towards the cornea to exert an optimum force thereon. A technical effect of the air pulse generator is to effectively generate the first excitation air pulse which interacts with the eye in a non-contact, hygienic manner.

[0080] Optionally, the first excitation air pulse is sent from the air pulse generator when operated at the first set of operational parameters. It may be appreciated that the first excitation air pulse is generated by modulating the first set of operational parameters determined based on the distance between the eye and the tonometer. The term "first set of operational parameters" as used herein refers to the characteristics of the air pulse generator which determine the force of the first excitation air pulse on the cornea. Specifically, the first set of operational parameters is determined based on the measured distance and a desired or optimum force of the first excitation air pulse required to cause a consistent and predictable deformation or displacement in the cornea. The force of the first excitation air pulse is relative to the distance between the eye and the tonometer. For example, when the distance is of a first value then the force of the first excitation air pulse is kept at a first value, and when the distance is increased (or decreased) to a second value, then relatively the force of the first excitation air pulse is also increased (or decreased) to a second value which is higher (or lower) than the first value of the force. In other words, with increasing distance between the eye and the tonometer, a higher force of the first excitation air pulse is required to cause a desired deformation or displacement in the cornea, and vice-versa.

[0082] Optionally, the first set of operational parameters comprises at least one of:

[0084] - a pressure of air in a pressure chamber of the air pulse generator;

[0086] - an opening speed of a control valve;

[0088] - a closing speed of the control valve;

[0090] - a velocity of the first excitation air pulse;

[0092] - a duration between a start of opening to an end of closing of the control valve,

[0094] wherein the control valve controls release of the first excitation air pulse from the pressure chamber towards the eye.

[0096] In this regard, the first set of operational parameters may include, but do not limit to, characteristics of the pressure chamber, the nozzle and the control valve. For example, the first set of operational parameters is an inner diameter of the exit aperture. In this regard, the first set of operational parameters is adjusted by adjusting a size of exit aperture of the nozzle. Similarly, the first set of operational parameters may be adjusted by either regulating a timing of sending the first excitation air pulse from the air pulse generator, or by regulating pressure of air in the pressure chamber. The pressure of air in the pressure chamber is based on the structural and operational characteristics of the air compressor in the pressure chamber. For example, the pressure of air in the pressure chamber ranges from 0.5 to 5 bars. As an example, the pressure can be from 0.5, 1, 1.5, 2, 2.5, 3, 3.5 or 4 bars up to 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5 or 5 bars. However, the pressure of air exiting the exit aperture of the nozzle may be same or different based on the exit aperture crosssection and length of the nozzle, the velocity of the first excitation air pulse, and a mass flow rate of the first excitation air pulse.

[0098] It may be appreciated that the opening and closing speeds of the control valve and the duration between thereof may influence the first excitation air pulse. The "opening speed" of the control valve refers to the speed at which the control valve opens, the "closing speed" of the control valve refers to the speed at which the control valve closes, and the "duration" refers to the time period for which the control valve remains open. Notably, the opening and closing speeds and the duration therebetween determine an amount of first excitation air, consistency of the first excitation air pulse, and shape, size and volume of the first excitation air pulse which exits the pressure chamber. Optionally, the opening speed and the closing speed may be of same or different. By regulating the opening speed and closing speed of the control valve, a duration of application of the first excitation air pulse on the cornea may be varied. For example, the first excitation air pulse may be a short pulse or may be a long pulse depending on properties of the cornea of the eye as determined by the user / operator of the tonometer. Notably, the properties of the cornea of each eye are different, thus, by controlling the opening and closing speed of the control valve, the user / operator manipulates the tonometer to send the short or long pulse of the first excitation air pulse for an effective and personalized IOP value measurement. Optionally, the opening time and closing time of the control valve ranges from l-15msec and less than 3msec (for closing). As an example opening time can be from 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13 or 14 milliseconds up to 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 or 15 milliseconds. Closing time should be selected to be "as fast as feasible" such as less than 3, 2.9, 2.8, 2.7, 2.6, 2.5, 2.4, 2.3, 2.2, 2.1, 2, 1.9, 1.8, 1.7, 1.6, 1.5, 1.4, 1.3, 1.2, 1.1, 1, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3 or 0.25 milliseconds.

[0100] Notably, by adjusting the duration for which the control valve remains open, the shape, size and volume of the first excitation air pulse may be regulated, to regulate a distribution of the force of the first excitation air pulse on the cornea. It may be appreciated that for IOP value measurement, the shape and volume of the first excitation air pulse needs to be uniform and well-focused so as to distribute the force of the first excitation air pulse evenly at the cornea for obtaining the consistent and predictable deformation or displacement thereof. Optionally, the duration between the opening and the closing of the control valve ranges from l-15msec. For example, a short duration between the opening and closing of the control valve produces a short first excitation air pulse, and vice-versa.

[0102] It may also be appreciated that one or more operational parameters from amongst the first set of operational parameters may be changed alone or in any suitable combination to produce the desired force of the first excitation air pulse at the cornea. For example, if the pressure of air is to be maintained, then the opening and closing speed of the control valve and / or velocity of the first excitation air pulse may be changed to produce the desired force at the cornea. Beneficially, adjustment of the first set of operational parameters based on the distance between the tonometer and the eye allows adjusting the force exerted by the first excitation air pulse to be optimized to cause readable deformation or displacement in the cornea for accurate IOP value measurement.

[0104] Beneficially, the fine-tuning of one or more operational parameters from amongst the first set of operational parameters allows for precise shaping of the air pulse, optimizing force delivery for different patients and conditions. This adapts the tonometer for the real-time adjustment of air pulse characteristics based on measured distance, improving measurement repeatability and patient comfort.

[0106] Optionally, the pressure of the air is set to a first pressure when the distance is a first distance, and the pressure of the air is set to a second pressure when the distance is a second distance, wherein the first pressure is higher than the second pressure and the first distance is longer than the second distance. As mentioned above, the air compressor generates the first excitation air pulse of a specific pressure determined based on the measured distance. Herein, the terms "first distance" and "second distance" refer to distances measured by the first sensor at 2 distinct time instances when the tonometer is aligned with the eye such that the first distance and the second distance are different from each other. Optionally, the first distance is longer than the second distance. Moreover, the terms "first pressure" and "second pressure" refer to pressures of air in the pressure chamber adjusted based on the measured first distance and second distance, respectively. It may be appreciated that the first pressure and the second pressure are different from each other. Moreover, when the first distance is longer than the second distance, then the first pressure is higher than the second pressure. Thus, with increasing distance between the eye and the tonometer, a higher pressure of the first excitation air pulse is required to cause a desired deformation or displacement in the cornea, and vice-versa. It may be appreciated that the disclosed tonometer automatically adjusts air pulse force to compensate for varying distances, ensuring the cornea receives a consistent stimulus regardless of patient positioning. This reduces the impact of user error or patient movement, leading to more reliable and repeatable IOP measurements. Moreover, such automatic adjustment of air pulse force based on the varying distances adapts the tonometer for applications including individual anatomical differences. This supports more accurate and patient-specific diagnostics essential for achieving consistent measurement outcomes.

[0108] Moreover, the velocity at which the first excitation air pulse is sent towards the eye may be determined by the pressure of air in the pressure chamber, a pressure outside the pressure chamber (atmospheric air pressure) and a density of air in the pressure chamber. The velocity of the first excitation air pulse is computed by the following equation:

[0111] <IMG file= he=50 id=imgf000017_0001 img-content=drawing img-format= inline=yes orientation=portrait wi=117>

[0112] wherein

[0114] v is the velocity of the first excitation air pulse,

[0116] is the pressure in the pressure chamber,

[0118] P2is the pressure outside the pressure chamber, and

[0120] p is the density of the air in the pressure chamber.

[0122] Alternatively, optionally, the air pulse generator comprises a piston to send the first excitation air pulse towards the cornea. It may be appreciated that the piston is an alternative to the control valve of the air pulse generator. The piston is configured to move in a manner that allows the first excitation air pulse to be sent towards the eye to exert the optimum force on the cornea. The piston-based air pulse generator allows for real-time, distance-dependent adjustment of both speed and length of piston movement. This enables precise control of the air pulse force, resulting in a more consistent and predictable corneal response, directly improving the accuracy and reliability of IOP measurements, as compared to the conventional tonometers (such as piezoelectric or valve-based tonometers). Moreover, it results in a reduction in calibration time and operator dependency.

[0124] Optionally, the first set of operational parameters comprises at least one of:

[0126] - a speed of a piston movement of the air pulse generator;

[0128] - a length of the piston movement,

[0130] wherein the piston movement towards a first direction generates the first excitation air pulse to be sent from the air pulse generator towards the eye.

[0132] In this regard, the first set of operational parameters is adjusted by adjusting the speed and length of the piston movement. Herein, the term "piston movement" refers to a back-and-forth movement of a piston in the air pulse generator. Herein, the term "first direction" refers to the direction towards the eye. It may be appreciated that the piston is at an initial position in a second direction, opposite to the first direction, when the pressure chamber has an initial amount of air of a given pressure therein. When the piston is moved from the initial position thereof in the first direction, by a given length and / or speed, a given volume of air exits the exit aperture of the nozzle as the first excitation air pulse. For example, a smaller length of the piston movement may produce a short air pulse as compared to a longer length of the piston movement that can produce a long air pulse. Moreover, by adjusting the length of the piston movement, the pressure of air and velocity of the first excitation air pulse is modified. For example, by increasing the length of the piston movement, the pressure of air and the velocity of the first excitation air pulse may be increased as a displacement volume of the air through the exit aperture of the nozzle is increased. The "displacement volume" refers to the amount of air in the first excitation air pulse that is sent out for each piston movement. Moreover, by adjusting the speed of piston movement, the pressure and velocity of the first excitation air pulse is modified. For example, by increasing the speed of the piston movement, the pressure and velocity of the first excitation air pulse may be increased.

[0134] Moreover, by adjusting the first set of operational parameters based on the distance between the eye and the tonometer, a desired optimum force exerted on the cornea is attained. Thereby resulting a technical effect of obtaining accurate IOP value measurement irrespective of the distance between the eye and the tonometer.

[0136] Furthermore, by adjusting the first set of operational parameters, a mass flow rate and the force of the first excitation air pulse can be adjusted. The mass flow rate may be determined as per the following equation:

[0138] m = pAv

[0140] wherein

[0142] m is the mass flow rate,

[0144] p is the density of the air in the pressure chamber,

[0146] A is the area of cross-section of the nozzle via which the first excitation air is sent towards the eye, and

[0148] v is the velocity of the first excitation air pulse.

[0150] Notably, the force of the first excitation air pulse may be determined as a function of mass flow rate and velocity. The force of the first excitation air pulse may be computed by following equation:

[0153] wherein

[0155] m is the mass flow rate,

[0157] p is the density of the air in the pressure chamber, A is the area of cross-section of the nozzle via which the first excitation air is sent towards the eye, and

[0159] v is the velocity of the first excitation air pulse.

[0161] It may be appreciated that the adjustment of the speed and / or length of the piston movement is performed dynamically based on the measured distance between the tonometer and the eye, such that the force and profile of the air pulse are precisely controlled to achieve consistent corneal deformation, thereby improving the accuracy and repeatability of intraocular pressure measurement, and reducing the need for iterative calibration.

[0163] In contrast to conventional air pulse tonometers, that rely on piezoelectric actuators or simple pressure / valve control, the present disclosure introduces a piston-based air pulse generator, wherein both the speed and length of piston movement are dynamically adjustable. Beneficially, this configuration enables the generation of air pulses with highly controlled force profiles, tailored to the specific distance between the tonometer and the patient's eye. The technical benefit of this approach is that by adjusting the piston speed and stroke length, the tonometer can compensate for variations in distance and patient anatomy, ensuring that the corneal deformation induced by the air pulse is consistent across different measurement conditions. Moreover, said approach reduces the need for manual or iterative calibration, as the tonometer can automatically adapt to each measurement scenario.

[0165] Furthermore, the use of a piston-based air pulse generator allows for a more linear and predictable relationship between control input (piston movement) and output (air pulse force), compared to the non-linearities often encountered in the conventional piezoelectric or valve-based air pulse tonometers. Thus, the piston-based air pulse generator results in improved repeatability and reliability of intraocular pressure measurements, essential for clinical diagnostics. It may be appreciated that since the conventional tonometers are fundamentally different in mechanical and control characteristics from a piston-based tonometer, therefore using a piston-based air pulse generator as used in the disclosed tonometer is non-obvious to a person skilled in the art, and that the dynamically-controlled piston mechanism of the disclosed tonometer enhances both the technical efficacy and user experience of air pulse tonometry.

[0167] Furthermore, the tonometer comprises the controller communicatively coupled to the first sensor, the second sensor and the air pulse generator. The term "controller" as used herein refers to a computational device that is operable for controlling the overall operation of the tonometer for IOP value measurement. 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. The controller is configured to: receive inputs from the first sensor and the second sensor pertaining to IOP value measuring parameters; to process sensor data; to determine the first set of operational parameters of the air pulse generator, based on the measured distance; to control the components of the air pulse generator such as the pressure chamber, the diameter of the exit aperture of the nozzle, the control valve or the piston movement, to send a first excitation air pulse towards the eye; to measure a first signal related to corneal oscillations caused by the sent first excitation air pulse; and to determine the IOP value from the measured first signal. The controller may be implemented as an internal component of the tonometer, an external component of the tonometer, or a combination thereof.

[0169] In this regard, the controller is configured to receive a value of the measured distance between the cornea and the tonometer, when the tonometer is aligned with the eye. The controller ensures proper alignment and optimal positioning of the tonometer relative to the eye, which is critical for consistent force delivery and accurate IOP measurement. Automatic distance measurement also streamlines the workflow and reduces setup time. Based on the measured distance, the first set of operational parameters of the air pulse generator is determined. The controller is configured to adjust the first set of operational parameters of the air pulse generator. Thus, the controller is configured to adjust the pressure in the pressure chamber, the opening speed and closing speed of the control valve or the length and the speed of the piston movement, the duration for which the control valve remains open, and the velocity of the first excitation air pulse.

[0171] Optionally, the controller may be configured to adjust the exit aperture of the nozzle to adjust the shape and size of the first excitation air pulse. Optionally, the controller may be coupled with an adjustment mechanism to adjust the first set of operational parameters and a closed loop feedback mechanism to ensure that movable components, such as the control valve or the piston, are operating properly. Optionally, the controller may be configured to monitor performance of the air compressor to ensure that the first excitation air pulse is sent towards the cornea with a desired pressure.

[0173] Moreover, after adjusting the first set of operational parameters, the controller is configured to trigger the air pulse generator to send the first excitation air pulse towards the eye. The first excitation air pulse impacts the cornea and deforms the cornea, causing the cornea to deform towards retina and then (after the air pulse is terminated) to oscillate. The interaction between the first excitation air pulse and the cornea results in corneal oscillations. The term "corneal oscillations" refers to deformation or displacement in the cornea caused due to the impact from the first excitation pulse. Beneficially, the controller enables precise timing and delivery of the air pulse at the cornea of the eye, ensuring that the corneal deformation is induced under controlled and repeatable conditions, for obtaining high-quality measurement signals. The second sensor measures the first signal related to the corneal oscillations caused by the first excitation air pulse and provides said sensor data to the controller for further processing thereof. In this regard, the controller captures the biomechanical response of the cornea to the air pulse, providing the raw data needed for accurate IOP calculation. Beneficially, high-fidelity signal acquisition by the controller improves the reliability and diagnostic value of the measurement. Moreover, by automating the analysis and calculation of IOP, the controller reduces the risk of human error and enabling rapid, objective results. This supports efficient clinical workflows and enhances patient throughput.

[0175] Beneficially, the controller centralizes and automates the measurement process, enabling real-time data processing and control. The integration of the controller in the tonometer, operably coupled with the sensor setup and the air pulse generator, allows for dynamic adjustment of measurement parameters, reducing manual intervention and the potential for operator-induced variability.

[0177] Optionally, the controller is configured to:

[0179] - determine, from the first signal, an oscillation frequency of the corneal oscillations; and

[0181] - calculate, from the oscillation frequency, the intraocular pressure value. In this regard, the first signal measured by the second sensor may be used to determine information on the oscillation frequency of the corneal oscillations. The term "oscillation frequency" as used herein refers to a measure of how often a corneal oscillation occurs in a given time period. It quantifies the rate of corneal oscillation and is crucial for understanding and analyzing periodic motions in various physical systems. The controller upon receiving the first signal, determines the oscillation frequency which is utilized to compute the IOP of the eye. Beneficially, the oscillation frequency provides a robust, quantifiable metric for IOP calculation. In this regard, the oscillation frequency provides information on the duration of one complete cycle and the number of cycles per unit time. Moreover, the oscillation frequency is relevant when analyzing the temporal variations, such as patterns and rhythms, of IOP. It may be appreciated that the frequency-based analysis is less susceptible to noise and artifacts than amplitude-only methods, improving diagnostic accuracy and reliability as well as robustness in signal analysis.

[0183] Optionally, the controller utilizes a pre-defined algorithm to correlate the determined oscillation frequency with IOP value. Further, optionally, a look up table can be used to determine IOP from the measured first signal (corneal oscillation frequency).

[0185] Optionally, the first signal is indicative of at least one of: an amplitude of the corneal oscillations, a damping of the corneal oscillations, an extent of flattening of at least a part of a cornea of the eye; a resistance of the eye, an eye condition, a force of the sent first excitation air pulse on the cornea, a corneal hysteresis, a corneal thickness. Notably, the amplitude and the damping of the corneal oscillations are dependent on the force exerted by the first excitation air pulse. Further, the impact of the first excitation air pulse causes the corneal oscillations of specific amplitude which last for a specific duration until the damping of the corneal oscillation occurs upon removal of the first excitation air pulse.

[0187] Moreover, in response to application of the first excitation air pulse, the at least a part of the cornea experiences flattening, or deplaning, such as changing from a convex shape to a concave shape, thereby causing corneal oscillation. The extent of flattening of the at least a part of the cornea depends on at least one of: the force exerted by the first excitation air pulse; the eye condition of each patient such as a disease (for example, glaucoma, or cataract) associated with the eye; the resistance of the eye; the properties of the cornea such as the corneal thickness, the corneal hysteresis. A technical effect of utilizing the first signal is that IOP measurement with respect to individual corneal properties can be carried out resulting in improved accuracy of IOP measurement.

[0189] Moreover, when the first excitation air pulse impacts the cornea, the cornea reflects the first excitation air pulse due to corneal resistance thereby changing a momentum of the first excitation air pulse which may be measured by the second sensor or any other sensor, associated with the tonometer, and utilized to estimate the IOP value of the eye as a function of change in the momentum, that is expressed in terms of impulse. The second sensor or the any other sensor measures the impulse as a function of the duration of application of the first excitation pulse, area of cross-section of the nozzle, the velocity and the density of the first excitation air pulse. The impulse corresponding to impact of the first excitation air pulse on the cornea is determined by the following equation:

[0191] J = F.At = pAv2. t

[0193] wherein

[0195] p is the density of the air in the pressure chamber,

[0197] A is the area of cross-section of the nozzle via which the first excitation air is sent towards the eye,

[0199] v is the velocity of the first excitation air pulse, and

[0201] At is the duration of application of the first excitation pulse.

[0203] 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.

[0205] Optionally, the method further comprises setting a pressure of the air to a first pressure when the distance is a first distance, and setting the pressure of the air to a second pressure when the distance is a second distance, wherein the first pressure is higher than the second pressure and the first distance is longer than the second distance. Optionally, the method further comprises:

[0207] - determining, from the first signal, an oscillation frequency of the corneal oscillations; and

[0209] - calculating, from the oscillation frequency, the intraocular pressure value.

[0211] DETAILED DESCRIPTION OF THE DRAWINGS

[0213] Referring to FIG. 1A, illustrated is a schematic diagram of a tonometer 100 for measuring an intraocular pressure value of an eye 104, when in use, in accordance with an embodiment of the present disclosure. As shown, the tonometer 100 is positioned with respect to a head 102 of an examinee and is aligned with respect to the eye 104 thereof. The tonometer 100 comprises a sensor setup comprising a distance sensor 106, a displacement sensor 107, an air pulse generator 110, and a controller 112 communicatively coupled to the distance sensor 106, the displacement sensor 107 and the air pulse generator 110. The controller 112 is configured to measure a distance between the eye 104 and the tonometer 100 with the distance sensor 107; determine a first set of operational parameters of the air pulse generator 110 based on the distance; control the air pulse generator 110 to send a first excitation air pulse 114 towards a cornea 108 the eye 104; measure a first signal related to corneal oscillations caused by the sent first excitation air pulse 114, with the displacement sensor 107; and determine the intraocular pressure value from the measured first signal. As shown, the air pulse generator 110 further includes a pressure chamber 116, a control valve 118, and a nozzle 120 having an exit aperture 122. In alternative setup the distance sensor 106 can be from hardware wise a different sensor from 107 as indicated in the figure 1. In some embodiments same (hardware) sensor is configured to work as the distance sensor (distance measurement) and as the displacement sensor (as a displacement sensor to measure corneal oscillations). Referring to FIG. 2A, illustrated is a schematic diagram of an implementation of a tonometer 200 for measuring an intraocular pressure value of an eye 204, in accordance with an embodiment of the present disclosure. As shown, a first excitation air pulse 202 is sent towards the eye 204 which results in corneal oscillation, depicted as a first signal 206 related to corneal oscillations. A displacement sensor 208 measures the first signal 206 for further intraocular pressure value measurement. In this example the displacement sensor could be a confocal chromatic sensor.

[0215] Referring to FIG. 2B, 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.

[0217] Referring to FIG. 3, illustrated is a flow chart 300 depicting steps of a method for measuring an intraocular pressure value of an eye, using a tonometer, such as the tonometer 100 of FIG. 1 in accordance with an embodiment of the present disclosure. At step 302, a distance between the eye and the tonometer is measured with a first sensor (such as a first confocal chromatic sensor which is configured to measure distance or with a distance sensor in general). At step 304, a first set of operational parameters of an air pulse generator is measured based on the distance. At step 306, the air pulse generator is controlled to send a first excitation air pulse towards the eye. At step 308, a first signal related to corneal oscillations caused by the sent first excitation air pulse is measured with a second sensor (such as the first confocal chromatic sensor which is configured to measure displacement (or distance) of cornea or a second confocal chromatic sensor which is configured to measure displacement (by way of distance variations) or in general with the displacement sensor). At step 310, the intraocular pressure value is determined from the measured first signal.

Claims

CLAIMS1. A tonometer (100, 200) for measuring an intraocular pressure value of an eye (104, 204), the tonometer comprising- a sensor setup (106);- an air pulse generator (110); and- a controller (112) communicatively coupled to the sensor setup and the air pulse generator, the controller configured to:- measure a distance between the eye and the tonometer with the sensor setup;- determine a first set of operational parameters of the air pulse generator based on the distance;- control the air pulse generator to send a first excitation air pulse (114, 202) towards the eye;- measure a first signal (206) related to corneal oscillations caused by the sent first excitation air pulse, with the sensor setup; and- determine the intraocular pressure value from the measured first signal.

2. The tonometer (100, 200) according to claim 1, wherein the sensor setup comprises at least one of:a first confocal chromatic sensor for measuring the distance and the corneal oscillations, ora first confocal chromatic sensor for measuring the distance and a second confocal chromatic sensor for measuring the corneal oscillations.

3. The tonometer (100, 200) according to claim 1 or 2, wherein the sensor setup comprises a distance sensor (106) and a displacement sensor (107. 208).

4. The tonometer (100, 200) according to any of the preceding claims, wherein the first set of operational parameters comprises at least one of: - a pressure of air in a pressure chamber (116) of the air pulse generator (HO);- an opening speed of a control valve (118);- a closing speed of the control valve;- a velocity of the first excitation air pulse (114, 202);- a duration between a start of opening to an end of closing of the control valve,wherein the control valve controls release of the first excitation air pulse (114, 202) from the pressure chamber towards the eye (104, 204).

5. The tonometer (100, 200) according to claim 4, wherein the pressure of the air is set to a first pressure when the distance is a first distance, and the pressure of the air is set to a second pressure when the distance is a second distance, wherein the first pressure is higher than the second pressure and the first distance is longer than the second distance.

6. The tonometer (100, 200) according to any of the claims 1-3, wherein the first set of operational parameters comprises at least one of: - a speed of a piston movement of the air pulse generator (110);- a length of the piston movement,wherein the piston movement towards a first direction generates the first excitation air pulse (114, 202) to be sent from the air pulse generator towards the eye (104, 204).

7. The tonometer (100, 200) according to any of the preceding claims, wherein the controller (112) is configured to:- determine, from the first signal (206), an oscillation frequency of the corneal oscillations; and- calculate, from the oscillation frequency, the intraocular pressure value.

8. The tonometer (100, 200) according to any of the preceding claims, wherein the first signal (206) is indicative of at least one of: an amplitude of the corneal oscillations, a damping of the corneal oscillations, an extent of flattening of at least a part of a cornea (108) of the eye (104, 204); a resistance of the eye, an eye condition, a force of the sent first excitation air pulse (114, 202) on the cornea, a corneal hysteresis, a corneal thickness.

9. A method for measuring an intraocular pressure value of an eye (104, 204), using a tonometer (100, 200), the method comprising - measuring a distance between the eye and the tonometer;- determining a first set of operational parameters of an air pulse generator (110) based on the distance;- controlling the air pulse generator to send a first excitation air pulse (114, 202) towards the eye;- measuring a first signal (206) related to corneal oscillations caused by the sent first excitation air pulse; and- determining the intraocular pressure value from the measured first signal.

10. The method according to claim 9, wherein the method further comprises setting a pressure of the air to a first pressure when the distance is a first distance, and setting the pressure of the air to a second pressure when the distance is a second distance, wherein the first pressure is higher than the second pressure and the first distance is longer than the second distance.

11. The method according to claim 9 or 10, wherein the method further comprises:- determining, from the first signal (206), an oscillation frequency of the corneal oscillations; and- calculating, from the oscillation frequency, the intraocular pressure value.

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