Non-contact tonometer and method of measuring internal pressure value of eye

Abstract

Disclosed is a non-contact tonometer (100, 200, 302, 502). The non- contact tonometer comprises an excitation and measuring unit (102, 202, 300, 504) comprising an electromagnetic exciter (104, 204, 306, 400, 506) comprising at least one electric coil (106, 206, 304, 404, 508) 5 powered with a variable current (i) and arranged to generate a variable magnetic field (416, 500), at least one magnetic armature (108, 208, 210, 212, 510) arranged to guide the variable magnetic field towards an eye (110, 214, 303, 418, 512) for at least partially passing through a cornea (112, 216, 301, 402) of the eye. Disclosed is a method of 10 measuring an internal pressure value of an eye.

Description

[0001] NON-CONTACT TONOMETER. AND METHOD OF MEASURING INTERNAL

[0002] PRESSURE VALUE OF EYE

[0003] TECHNICAL FIELD

[0004] The present disclosure relates to a non-contact tonometer. The present disclosure also relates to a method of measuring an internal pressure value of an eye.

[0005] BACKGROUND

[0006] A tonometer is a medical instrument used to measure the pressure inside the eye, also known as intraocular pressure (IOP). Typically, a tonometry is a quick, painless and non-invasive test that is typically performed during a comprehensive eye examination. There are different types of tonometers based on different working principles. There is a known type of tonometer that applies a vibrational excitation to the eye and measures the vibrational response thereof. Moreover, the tonometer measures the resulting vibrations of the cornea, and from the measurement, it calculates the intraocular pressure (IOP) of the eye.

[0007] There exist some techniques that depict a correlation between a resonance frequency of the eye and its internal pressure. This correlation allows calculating the internal pressure of the eye using the measured resonance frequency of the eye. In this regard, such techniques use sonic excitation and a laser doppler velocimeter for measuring the eye. The resonance frequency at which a first peak of oscillation amplitude of a cornea is observed is determined. The sonic excitation is applied using a speaker. Additionally, the speaker is mounted on a soft cup that is then pressed against the face of the subject, in contact with an annular zone surrounding the eye, in order to improve the efficiency of a power transfer from the speaker to the eye. This enables the vibrations of the speaker's membrane to be transmitted to the eye by means of air pressure variations inside a chamber defined by the speaker's membrane, the soft cup and the face of the subject. The variable air pressure applies a variable force on the cornea of the eye, that cause a vibration in the eye. By varying the frequency of the air pressure applied to the eye it is possible to measure the resonance frequency of the eye.

[0008] However, such techniques are not contactless. Moreover, since the soft cup is pressed against the skin of the subject, there is a considerable risk to transmit a disease (such as covid- 19) from the subject to another subject. Furthermore, in some cases, the soft cup is sterilized prior to use on the other subject. However, the act of sterilization requires human intervention, and thus fails to exclude completely the risk of transmission of diseases. Furthermore, the act of sterilization increases the time and cost of operation as well.

[0009] Additionally, the variable pressure has the disadvantage of applying a variable force even on the annular zone surrounding the eye. In this regard, the eye pressure is then determined by using a vibrational response of the eye. However, such techniques fail to measure the internal pressure of the eye accurately. The main reason is that the pressure variations are not applied only on the cornea, but simultaneously on the eye and on an annular zone surrounding the eye. The said pressure variations cause the desired oscillation of the eye cornea (which is related to the eye pressure) and simultaneously an undesired secondary oscillation of the whole eye together with a volume of tissues surrounding the eye. The secondary oscillation depends on the stiffness of the tissues surrounding the eye and the volume of the tissues and does not depend on the eye pressure. Thus, the secondary oscillation disturbs the measurement, making the relation between the eye pressure and the measured vibrational response of the cornea less precise.

[0010] Therefore, in light of the foregoing discussion, there exists a need to overcome the aforementioned drawbacks associated with existing techniques and devices associated therewith for measuring the eye pressure.

[0011] SUMMARY

[0012] The present disclosure seeks to provide a non-contact tonometer. The present disclosure also seeks to provide a method of measuring an internal pressure value of an eye. An aim of the present disclosure is to provide a solution that overcomes at least partially the problems encountered in prior art.

[0013] In one aspect, an embodiment of the present disclosure provides a noncontact tonometer comprising:

[0014] - an excitation and measuring unit comprising

[0015] - an electromagnetic exciter comprising

[0016] - at least one electric coil powered with a variable current (i) and arranged to generate a variable magnetic field, and

[0017] - at least one magnetic armature arranged to guide the variable magnetic field towards an eye for at least partially passing through a cornea of the eye.

[0018] In another aspect, an embodiment of the present disclosure provides a method of measuring an internal pressure value of an eye, the method comprising:

[0019] - oscillating a cornea of an eye by providing a variable magnetic field,

[0020] - varying a frequency of the variable magnetic field in a predefined range of frequency,

[0021] - measuring at least a peak amplitude value of an oscillation of the cornea of the eye,

[0022] - finding a lowest value of the frequency corresponding to a peak amplitude value to find a resonance frequency value of the cornea of the eye, and - calculating the internal pressure value of the eye using the resonance frequency.

[0023] Embodiments of the present disclosure substantially eliminate or at least partially address the aforementioned problems in the prior art, and enable an improved, simple, compact, accurate, reliable and efficient non-contact tonometer. Beneficially, the non-contact tonometer employs the electromagnetic exciter for supporting an application of the excitation force on the cornea in a contactless manner. Moreover, the excitation force is limited only to a desired part of the cornea in order to enable the measurement of the eye pressure with a better precision.

[0024] Additional aspects, advantages, features and objects of the present disclosure would be made apparent from the drawings and the detailed description of the illustrative embodiments construed in conjunction with the appended claims that follow.

[0025] It will be appreciated that features of the present disclosure are susceptible to being combined in various combinations without departing from the scope of the present disclosure as defined by the appended claims.

[0026] BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The summary above, as well as the following detailed description of illustrative embodiments, is better understood when read in conjunction with the appended drawings. For the purpose of illustrating the present disclosure, exemplary constructions of the disclosure are shown in the drawings. However, the present disclosure is not limited to specific methods and instrumentalities disclosed herein. Moreover, those skilled in the art will understand that the drawings are not to scale. Wherever possible, similar elements have been indicated by identical numbers. Embodiments of the present disclosure will now be described, by way of example only, with reference to the following diagrams wherein:

[0028] FIG. 1A is a view of a first preferred embodiment of a non-contact tonometer, in accordance with an embodiment of the present disclosure; FIGs. IB, and 1C are views of a first preferred embodiment of the excitation and measuring unit, in accordance with an embodiment of the present disclosure;

[0029] FIGs. 2A and 2C are views of a second preferred embodiment of a noncontact tonometer, in accordance with an embodiment of the present disclosure;

[0030] FIGs. 2B and 2D are views of a second preferred embodiment of the excitation and measuring unit, in accordance with an embodiment of the present disclosure;

[0031] FIGs. 3A and 3B are views of a third preferred embodiment of the excitation and measuring unit, in accordance with an embodiment of the present disclosure;

[0032] FIG 3C is a view of a third preferred embodiment of a non-contact tonometer, in accordance with an embodiment of the present disclosure; FIG. 4 is another view of a third preferred embodiment of an electromagnetic exciter, in accordance with an embodiment of the present disclosure;

[0033] FIGs. 5A is a view of a variable magnetic field generated towards an eye using a non-contact tonometer, in accordance with the first preferred embodiment of the present disclosure;

[0034] FIGs. 5B and 5C are views of a first preferred embodiment of a current induced by a variable magnetic field inside the eye, in accordance with the first and the second preferred embodiment of the present disclosure; FIGs. 6A and 6B are other views of a variable magnetic field generated towards an eye using a non-contact tonometer, in accordance with the third preferred embodiment of the present disclosure; and FIG. 7 is a flowchart depicting steps of a method of measuring an internal pressure value of an eye, in accordance with an embodiment of the present disclosure.

[0035] In the accompanying drawings, an underlined number is employed to represent an item over which the underlined number is positioned or an item to which the underlined number is adjacent. A non-underlined number relates to an item identified by a line linking the non-underlined number to the item. When a number is non-underlined and accompanied by an associated arrow, the non-underlined number is used to identify a general item at which the arrow is pointing.

[0036] DETAILED DESCRIPTION OF EMBODIMENTS

[0037] 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.

[0038] In one aspect, an embodiment of the present disclosure provides a noncontact tonometer comprising:

[0039] - an excitation and measuring unit comprising

[0040] - an electromagnetic exciter comprising

[0041] - at least one electric coil powered with a variable current (i) and arranged to generate a variable magnetic field, and

[0042] - at least one magnetic armature arranged to guide the variable magnetic field towards an eye for at least partially passing through a cornea of the eye.

[0043] In another aspect, an embodiment of the present disclosure provides a method of measuring an internal pressure value of an eye, the method comprising:

[0044] - oscillating a cornea of an eye by providing a variable magnetic field, - varying a frequency of the variable magnetic field in a predefined range of frequency,

[0045] - measuring at least a peak amplitude value of an oscillation of the cornea of the eye,

[0046] - finding a lowest value of the frequency corresponding to the peak amplitude value to find a resonance frequency value of the cornea of the eye, and

[0047] - calculating the internal pressure value of the eye using the resonance frequency.

[0048] The present disclosure provides the aforementioned non-contact tonometer and the aforementioned method that is simple, compact, robust, accurate, reliable and user-friendly. Beneficially, the non-contact tonometer employs the electromagnetic exciter that enables the application of the excitation force on the cornea in a contactless manner. Moreover, the non-contact tonometer eliminates the risk of transmission of diseases from one subject to another subject. Additionally, the noncontact tonometer employs the electromagnetic exciter, having at least one electric coil and at least one magnetic armature that works in conjunction with each other for determining a vibrational response of the eye and an internal pressure of the eye correlated to the vibrational response of the eye.

[0049] Pursuant to the embodiments of the present disclosure, the term "noncontact tonometer" as used herein refers to an instrument that is used for measuring an internal pressure value of an eye in a contactless manner. The term "internal pressure" (namely an intraocular pressure (IOP) ) as used herein refers to a fluid pressure of the eye. The IOP exerts forces on every part of the eye. It will be appreciated that the cornea is a surface of the eye that is suitable to measure the IOP. The measurement of the IOP on the cornea could be made easier and with better precision than on other eye surfaces, such as the sclera. Notably, the measurement of the internal pressure is of vital importance to maintain overall eye health and function. It will be appreciated that the non-contact tonometer may be used for measurement of the intraocular pressure. Typically, the said measurement enables a diagnosis and treatment of ocular hypertension before the development of eye-related condition such as glaucoma.

[0050] The non-contact tonometer comprises an excitation and measuring unit. The term "excitation and measuring unit" as used herein refers to an arrangement that is used for excitation of the cornea of the eye and also to measure the vibrational response of the cornea, in order to measure the internal pressure thereof. Herein, the excitation refers to a process of applying a variable force on the cornea of the eye. The excitation and measuring unit comprises an electromagnetic exciter. The term "electromagnetic exciter" as used herein refers to a device that generates an electromagnetic force applied on the anterior segment of an eye, able to cause a mechanical movement of the cornea of the eye. In this regard, the electromagnetic force is an excitation force that causes the mechanical movement such as mechanical oscillation or vibration of the cornea. In an example, the eye is considered to be a thin-walled elastic vessel filled with a pressured fluid. As a consequence, the eye has a mechanical vibrational behaviour and a resonance frequency.

[0051] The electromagnetic exciter comprises at least one electric coil powered with a variable current (i) and arranged to generate a variable magnetic field. The term "electric coil" as used herein refers to an electrical conductor such as a wire in a shape of a coil (a spiral or a helix). Optionally, the at least one electric coil is made up of one or more turns of wire. Optionally, the shape and the number of the at least one electric coil may vary based on an application thereof. Optionally, the at least one electric coil is fabricated using insulated copper wire. Typically, the at least one electric coil is wound around a core. The electric terminals of the coil are connected to a power source for receiving an electric current therefrom. Herein, the electric current is variable, preferably an alternating electric current. It will be appreciated that when in operation, the electric coil is powered with the variable electric current to generate the variable magnetic field. Moreover, the amount of electric current may be varied by increasing or decreasing a power that is supplied using the power source.

[0052] The electromagnetic exciter comprises at least one magnetic armature. The term "magnetic armature" as used herein refers to a structure made of ferromagnetic material that is associated with a winding (or a set of windings) of the at least one electric coil. Optionally, the at least one magnetic armature is a U-shaped magnetic armature having a first arm with a first end and a second arm with a second end. It will be appreciated that the at least one magnetic armature is able to guide the variable magnetic field towards the eye irrespective of the shape of the at least one magnetic armature.

[0053] It will be appreciated that the at least one electric coil and the at least one magnetic armature are mounted together in such a manner that the at least one magnetic armature is operable for guiding the variable magnetic field that is generated by the at least one electric coil towards the cornea of the eye. Moreover, the variable magnetic field is guided in such a manner that it could at least partially pass through the cornea of the eye. The variable magnetic field induces electrical currents inside the cornea and the aqueous humour of the eye, which are conductive materials. The interaction between the induced current with the variable magnetic field generates a variable axial force on the cornea. The variable axial force applied on the cornea causes the mechanical oscillation of the cornea. The frequency of the alternate current that power the electric coil is equal to the frequency of variation of the variable magnetic field generated by the electric coil and is also equal to the frequency of the variable electromagnetic force applied on the cornea and is also equal to the frequency of the mechanical oscillation of the cornea.

[0054] Optionally, the at least one magnetic armature includes an internal magnetic armature, an external magnetic armature and a posterior magnetic armature. Optionally, the internal magnetic armature has a conical shape with an internal hole that may be substantially conical. Optionally, the number and shapes of the magnetic armatures may vary based on an application thereof. Optionally, the at least one electric coil is placed inside the external magnetic armature. Optionally, the at least one electric coil is placed surrounding the internal magnetic armature.

[0055] Optionally, the electromagnetic exciter further comprises at least one permanent magnet. Optionally, the permanent magnet is a neodymium magnet or a samarium-cobalt magnet, which are well-known types of strong magnets. Optionally, the electromagnetic exciter comprises one or more permanent magnets that, together with the magnetic armatures, apply to the cornea a strong constant magnetic field. Beneficially, the at least one permanent magnet is used to generate a constant magnetic field with a high value of magnetic induction inside the eye in comparison to the value of magnetic induction of the variable magnetic field that is produced when only the at least one electric coil is employed in the noncontact tonometer.

[0056] In this regard, when the electric coil is powered with the variable current, the variable magnetic field generated by the coil is summed to the constant magnetic field generated by the permanent magnet. The result is a magnetic field that has variations of magnetic induction around a constant value of the magnetic induction. The variations of magnetic induction inside the anterior segment of the eye generate a variable current inside the cornea and aqueous that are conductive materials. The interaction between the variable current and the strong constant component of the magnetic field created by the permanent magnet generates a variable electromagnetic force that is higher than the electromagnetic force obtained in a previous preferred embodiment without permanent magnets. This higher value of the electromagnetic force improves the efficiency of the vibrational excitation of the cornea.

[0057] Optionally, the excitation and measuring unit further comprises an optical displacement sensor. The term "optical displacement sensor" as used herein refers to a displacement sensor that measures a distance between the sensor and an object by means of optical elements and a beam of light. Optionally, the optical displacement sensor is placed between the first arm and the second arm of the at least one U-shaped magnetic armature in order to identify the oscillations of the cornea. It will be appreciated that the optical displacement sensor is placed at an appropriate position, thus identifying the oscillations of the cornea accurately. Optionally, a distance between the first arm and the second arm is minimum towards the first end and the second end, which are close to the eye. In this regard, said geometry imparts efficient measurement of the oscillations of the cornea.

[0058] Optionally, the optical displacement sensor is selected to be at least one of a confocal chromatic displacement sensor, a laser doppler vibrometer. The term "confocal chromatic displacement sensor" as used herein refers to an instrument that works by focusing a light with a wide band of wavelengths, usually white light, onto a target surface (such as the eye) using a high dispersion objective lens. It will be appreciated that the confocal chromatic displacement sensor is used for resolutions of measurement of the displacement of tens of nanometres at a measuring frequency of tens of kilohertz (kHz). Optionally, the confocal chromatic displacement sensor is used for measuring the distance between the confocal chromatic displacement sensor and the eye from few millimetres to tens of millimetres. Beneficially, the confocal chromatic displacement sensor may be customized in order to make it cost-efficient.

[0059] The term "laser doppler vibrometer" as used herein refers to a type of sensor that is used to make non-contact vibration measurements of a target surface (such as the eye). In this regard, the laser beam from the laser doppler vibrometer is directed at the target surface, and a vibration amplitude and frequency are extracted from a doppler shift of the reflected laser beam frequency due to a motion of the surface. Typically, the output of the laser doppler vibrometer is generally a continuous analog voltage that is directly proportional to the target velocity component along the direction of the laser beam. Moreover, the laser doppler vibrometer support an accurate measurement of an amplitude of the vibrations of the cornea.

[0060] Optionally, the confocal chromatic displacement sensor may be designed in such a way that makes it operable to measure with a beam of an infrared light. In this regard, the confocal chromatic displacement sensor uses a wide band infrared light as a measuring beam to measure the displacement of the cornea of the eye. Beneficially, the infrared light is unseeable by the eye of the subject such as a patient. In such a case, the temptation of the subject to blink the eye is reduced during an initial phase such as when setting a right relative position between the noncontact tonometer and the eye. Optionally, the infrared light is used to reduce the eventual blinking of the eye during the measurement thereof. Additionally, the infrared light is less likely to cause damage to the eyes being measured. Moreover, the beam of light of the confocal chromatic sensor is oriented normal to the cornea. Optionally, a significant tilt of the beam's axis with regard to the normal direction of the eye is readily tolerated by the confocal chromatic displacement sensors. As a result, even if the non-contact tonometer is hand-held and not properly cantered or oriented, the measurement may not be affected. Optionally, the optical displacement sensor is operable to measure at least one of selected from:

[0061] - an amplitude of oscillation of at least one point of the cornea;

[0062] - a thickness of the cornea in at least one point; and

[0063] - a distance between the cornea and the excitation and measuring unit.

[0064] In this regard, the excitation and measuring unit comprises the optical displacement sensor that is placed together with the electromagnetic exciter in a position close to the cornea of the eye. Optionally, the optical displacement sensor is operable to measure the amplitude of oscillation of at least one point of the cornea. In this regard, the amplitude of oscillation of the at least one point on the cornea refers to the difference between the maximum and the minimum distance between the optical sensor and the cornea during the oscillation of the cornea. Optionally, the amplitude of oscillation is measured for determining the movement or deviation of the at least one point during the process of eye blinking or another eye movement. It will be appreciated that the confocal chromatic displacement sensors may conduct thousands of observations per second with a resolution of tens of nanometres and thus allows precise measurement of the amplitude of oscillation of the at least one point of the cornea. Optionally, the amplitude of oscillation of the at least one point of the cornea is used for determining the resonance frequency of the cornea. In this regard, when the cornea is excited by a variable force, it is forced to oscillate with the frequency of the variable force. Moreover, when the frequency of the variable force is equal to the resonance frequency of the cornea the amplitude of oscillation of the cornea has a peak value. Furthermore, by scanning the frequency of the electromagnetic force that excites the cornea in a range of frequencies it is possible to identify the resonance frequency of the cornea as the frequency that corresponds to a peak of amplitude of oscillation of the cornea. The resonance frequency of the cornea depends on the internal pressure of the eye and the thickness of the cornea is typically in a range of 100-500 Hz.

[0065] Optionally, the optical displacement sensor is operable to measure the thickness of the cornea in the at least one point of the cornea. Beneficially, the thickness is measured using the confocal chromatic displacement sensor, as it possesses the ability to simultaneously measure the position of both an external surface and an internal surface of the cornea. The thickness of the cornea characterise the stiffness of the cornea, which is a disturbing factor when measuring the internal pressure of the eye. Moreover, when the thickness of the cornea is measured, its value may be used to apply a correction when calculating the internal pressure value of the eye. This allows to calculate the internal pressure of the eye with improved precision.

[0066] Optionally, the optical displacement sensor is operable to measure the distance between a front part of the non-contact tonometer and the cornea. It will be appreciated that the measured distance is used as a feedback (such as a visual feedback, an acoustic feedback) during the initial phase of the measurement. Moreover, the measured distance is indicative of the correct position of the non-contact tonometer relative to the eye.

[0067] Optionally, when the non-contact tonometer is hand-held then the measured distance may be used to give an operator a feedback to confirm that the non-contact tonometer is placed in the correct position relative to the eye, or to indicate that a change of position is required. Additionally, the measured distance may be used as a feedback in an automatic position control system. In this regard, the automatic position control system includes at least one actuator for changing the relative position of the non-contact tonometer relative to the eye. In such a case, the actuator is commanded by using the measured distance as feedback. Optionally, the at least one electric coil is used as a sensor, by measuring a variation of electric impedance of the at least one electric coil caused by the oscillation of the cornea. In this regard, the maximum value of the electric impedance of the coil corresponds to a peak of the amplitude of oscillation of the cornea.

[0068] Optionally, in the non-contact tonometer:

[0069] - the permanent magnet has a substantially annular shape, with a first pole and a second pole on the opposite faces;

[0070] - the electromagnetic exciter has a proximal end and a distal end, the electromagnetic exciter further comprises a volume of space extending along a center line of the electromagnetic exciter from the proximal end until the distal end; and

[0071] - the at least one magnetic armature comprising

[0072] - an internal magnetic armature arranged to surround at least partially the volume of space in the proximal end and to be magnetically coupled with the first pole of the permanent magnet via the second end,

[0073] - an external magnetic armature arranged to surround at least partially the electric coil and being magnetically coupled to the second pole of the permanent magnet; and wherein

[0074] - the electric coil is arranged to at least partially surround the internal magnetic armature.

[0075] Herein, an annular shape refers to a ring-shaped geometrical pattern. Optionally, the permanent magnet has the annular shape with an internal hole that may have a cylindrical shape. Optionally, the permanent magnet has the first pole and the second pole that are located on the opposite faces of the permanent magnet. Optionally, the electromagnetic exciter includes the proximal end and the distal end. In this regard, the proximal end is nearer to the cornea of the eye in comparison to the distal end that is farther from the eye. Optionally, the electromagnetic exciter further comprises the volume of space extending along the center line of the electromagnetic exciter from the proximal end until the distal end. Optionally, the at least one magnetic armature comprises the internal magnetic armature. Herein, the internal magnetic armature is arranged in such a way that it surrounds at least partially the volume of space in the proximal end thereof. Moreover, the internal magnetic armature is arranged in such a manner that it could be magnetically coupled with the first pole of the permanent magnet via the second end.

[0076] Optionally, the at least one magnetic armature comprises the external magnetic armature. Herein, the external magnetic armature is arranged in such a manner that it surrounds at least partially the electric coil. Moreover, the at least one external magnetic armature is being magnetically coupled to the permanent magnet. Optionally, the electric coil is arranged to at least partially surround the internal magnetic armature. It will be appreciated that the aforementioned arrangement supports an improved measuring of the internal pressure of the cornea of the eye. Optionally, the electromagnetic exciter may function even if the at least one electric coil surrounds only the internal magnetic armature. Optionally, the electromagnetic exciter may also function with a single electric coil and a coaxial construction of the at least one magnetic armature and the electric coil, even if there is no permanent magnet.

[0077] Optionally, the optical displacement sensor is arranged inside the volume of space. In this regard, the aforementioned arrangement supports the optical displacement sensor to be placed near or at least partially inside the internal magnetic armature. In this case, the beam of light emitted by the optical displacement sensor may pass through the internal magnetic armature and reach the cornea of the eye to enable the measurement of its displacement. The present disclosure also relates to the method as described above. Various embodiments and variants disclosed above apply mutatis mutandis to the method.

[0078] Optionally, the variable magnetic field is produced by a coil powered with a variable current (i) and a frequency scan of the variable current is performed over a frequency range.

[0079] Optionally, the method further comprises

[0080] - measuring a thickness of a cornea of the eye in at least one point;

[0081] - measuring a resonance frequency value of the cornea; and

[0082] - calculating the internal pressure value of the eye using both the value of the resonance frequency of the cornea and the value of the thickness of the cornea.

[0083] Optionally, the method further comprises

[0084] - measuring a distance value between the cornea and an excitation and measuring unit, and

[0085] - using the measured distance value as a feedback signal to place the excitation and measuring unit at a desired position relative to the cornea.

[0086] Optionally, an electrical impedance of the coil is continuously measured during frequency scanning of the variable current (i). In this case the resonance frequency value of the cornea is measured as the lowest frequency of the current (i) that causes a peak amplitude value of the electrical impedance of the coil.

[0087] In this regard, the peak of amplitude of oscillation of the cornea is measured using the at least one electric coil. In such a case, the vibrating anterior segment of the eye is crossed by the induced current (I) and causes a change in the electric impedance of the at least one electric coil. Moreover, when the oscillation of the cornea reaches the peak of amplitude, the at least one electric coil impedance reaches a maximum value. Therefore, it is possible to determine the initial peak of amplitude of corneal oscillation by measuring using various electrical means the fluctuations of impedance of the at least one electric coil. Throughout the current frequency scan, the electrical impedance of the at least one electric coil is constantly measured to complete the measurement. The lowest frequency of the current that results in a peak in the electrical impedance of the at least one coil is identified as the resonance frequency of oscillation of the cornea.

[0088] DETAILED DESCRIPTION OF THE DRAWINGS

[0089] Referring to FIG. 1A, is a preferred embodiment of a non-contact tonometer 100, in accordance with an embodiment of the present disclosure. Referring to FIGs. IB and 1C, shown are perspective views of a first preferred embodiment of the excitation and measuring unit 102, in accordance with an embodiment of the present disclosure. The noncontact tonometer 100 comprises an excitation and measuring unit 102 that comprises an electromagnetic exciter 104. The electromagnetic exciter 104 comprises at least one electric coil 106 powered with a variable current (i) (not shown) and arranged to generate a variable magnetic field (not shown). Moreover, the electromagnetic exciter 104 comprises at least one magnetic armature 108 arranged to guide the variable magnetic field towards an eye 110 for at least partially passing through a cornea 112 of the eye 110. The excitation and measuring unit 102 further comprises an optical displacement sensor 114 placed together with the electromagnetic exciter 104 in a position close to the cornea 112 of the eye 110.

[0090] As shown in FIG. 1C a perspective view of the excitation and measuring unit 102. As shown, the at least one magnetic armature 108 is a U- shaped magnetic armature having a first arm 116 with a first end and a second arm 118 with a second end. As shown, the at least one electric coil 106 is mounted on the first arm 116 and the second arm 118 of the U-shaped magnetic armature. Additionally, the non-contact tonometer 100 includes electric terminals 120 for powering the at least one electric coil 106.

[0091] Figures. 1A, IB, and 1C 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.

[0092] Referring to FIGs. 2A and 2C, shown are views of a second preferred embodiment of a non-contact tonometer 200, in accordance with an embodiment of the present disclosure. Referring to FIGs. 2B and 2D, shown are views of a second preferred embodiment of an excitation and measuring unit 202, in accordance with an embodiment of the present disclosure. The non-contact tonometer 200 comprises an excitation and measuring unit 202. The excitation and measuring unit 202 comprises an electromagnetic exciter 204. The electromagnetic exciter 204 comprises at least one electric coil 206 powered with a variable current (i) and arranged to generate a variable magnetic field. Moreover, the electromagnetic exciter 204 comprises at least one magnetic armature such as 208, 210, 212 arranged to guide the variable magnetic field towards an eye 214 for at least partially passing through a cornea 216 of the eye 214. The electromagnetic exciter 204 further comprises at least one permanent magnet such as 218 and 220. The magnetic field guided by the at least one magnetic armature towards the eye has inside the eye a tangential component of the magnetic induction (Bt). Herein, FIG. 2A depicts a top view of the non-contact tonometer 200 and FIG. 2B depicts a perspective view of the non-contact tonometer 200. As shown, the excitation and measuring unit 202 further comprises an optical displacement sensor 222 placed together with the electromagnetic exciter 204 in a position close to the cornea 216 of the eye 214.

[0093] Herein, FIG. 2C depicts a top view of the non-contact tonometer 200 and FIG. 2D depicts a perspective view of the excitation and measuring unit 202. As shown, the at least one magnetic armature such as 208, 210, 212 is a U-shaped magnetic armature having a first arm with a first end and a second arm with a second end. Additionally, the non-contact tonometer 200 includes electric terminals 224 for powering the at least one electric coil 206.

[0094] FIGs. 2A, 2B, 2C and 2D 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.

[0095] Referring to FIGs. 3A and 3B, shown are views of a third preferred embodiment of the excitation and measuring unit 300, in accordance with an embodiment of the present disclosure. Referring to FIG 3C, shown is a view of a third preferred embodiment of a non-contact tonometer 302, in accordance with an embodiment of the present disclosure. As shown in FIG. 3A, a longitudinal cross-section of the excitation and measuring unit 300 in an operative position thereof close to a cornea 301 of an eye 303. The excitation and measuring unit 300 is having at least one electric coil 304. The excitation and measuring unit 300 comprises an electromagnetic exciter 309 having a proximal end 308 and a distal end 310, the electromagnetic exciter 309 further comprises a volume of space extending along a center line of the electromagnetic exciter 306 from the proximal end 308 until the distal end 310. There is shown at least one magnetic armature comprising an internal magnetic armature 312 arranged to surround at least partially the volume of space in the proximal end 308. There is shown an external magnetic armature 314 arranged to surround at least partially the at least one electric coil 304 and being magnetically coupled to at least one permanent magnet 316. The at least one permanent magnet 316 has a substantially annular shape, with a first pole and a second pole on the opposite faces. The at least one permanent magnet 316 is an optional component of the excitation and measuring unit 300 and is used to increase an efficiency thereof. The at least one electric coil 304 is arranged to at least partially surround the internal magnetic armature 312. Additionally, the excitation and measuring unit 300 includes electric terminals 318 for powering the at least one electric coil 304. As shown on FIG 3C, the non-contact tonometer 300 comprises an optical displacement sensor 320. As shown in FIG. 3B, a perspective view of the excitation and measuring unit 300 in an operative position thereof close to the eye 303. As shown in FIG. 3C, a top view of the non-contact tonometer 300 in an operative position thereof close to an eye 303.

[0096] FIGs. 3A, 3B, and 3C 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.

[0097] Referring to FIG. 4, shown is other view of a third preferred embodiment of an electromagnetic exciter 400, in accordance with an embodiment of the present disclosure. Herein, the FIG. 4 is showing a coaxial version of the electromagnetic exciter 400. As shown, a cross-sectional view of the electromagnetic exciter 400 that applies a vibrational excitation on a cornea 402. The electromagnetic exciter 400 comprises the at least one electric coil 404 and at least one magnetic armature. The at least one magnetic armature contain an internal magnetic armature 406, an external magnetic armature 408 and a posterior magnetic armature 410. Herein, the internal magnetic armature 406 has a conical shape with an internal hole that may be substantially conical. Optionally, at least one electric coil 404 is placed inside the external magnetic armature 408 and surrounding at least partially the internal magnetic armature 406. Optionally, the electromagnetic exciter 400 has at least one permanent magnet 412. Additionally, the electromagnetic exciter 400 includes electric terminals 414 for powering the at least one electric coil 404. Moreover, the at least one electric coil 404 powered with a variable current (i) and arranged to generate the variable magnetic field 416. Herein, the variable magnetic field 416 is a toroidal magnetic field. Moreover, the electromagnetic exciter 400 comprises the at least one magnetic armature arranged to guide the variable magnetic field 416 towards the eye 418 for at least partially passing through the cornea 402 of the eye 418.

[0098] FIG. 4 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.

[0099] Referring to FIGs. 5A, shown are views of a variable magnetic field 500 generated using a non-contact tonometer 502, in accordance with the first preferred embodiment of the present disclosure. As shown in FIG. 5A, a first preferred embodiment of the non-contact tonometer 502 that comprises an excitation and measuring unit 504. The excitation and measuring unit 504 comprises an electromagnetic exciter 506 that comprises at least one electric coil 508 powered with a variable current (i) and arranged to generate the variable magnetic field 500. Moreover, the electromagnetic exciter 506 comprises at least one magnetic armature 510 arranged to guide the variable magnetic field 500 towards an eye 512 for at least partially passing through a cornea 514 of the eye 512. Referring to FIGs. 5B and 5C, shown are the first preferred embodiment of a current induced by the variable magnetic field inside the eye 512. Herein, the variable magnetic field is generated by the electromagnetic exciter together with an induced current (I) and a generated electromagnetic force (Fem) applied on the cornea 514 of the eye 512. Herein, the variable magnetic field has a tangential component of the magnetic induction (Bt) Furthermore, the interaction between the induced current and the tangential component of the variable magnetic field generates the electromagnetic force.

[0100] FIGs. 5A, 5B and 5C 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.

[0101] Referring to FIGs. 6A and 6B, shown are other views of a variable magnetic field generated using a non-contact tonometer (not shown), in accordance with the third preferred embodiment of the present disclosure. As shown in FIG. 6A, and FIG. 6B, the variable magnetic field is generated by an electromagnetic exciter (not shown) together with an induced current and a generated electromagnetic force (Fem) applied on a cornea (depicted as 112 in figure 1A) of an eye (depicted as 110 in figure 1A). The variable magnetic field is generated by the electromagnetic exciter together with an induced current (I) and a generated electromagnetic force (Fem) applied on the cornea 514 of the eye 512. The constant magnetic field of at least one permanent magnet (not shown) is guided by at least one magnetic armature to the cornea of the eye and closes at least partially through the cornea, together with the variable magnetic field generated by at least one electric coil (not shown). Herein, the constant magnetic field generated by the at least one permanent magnet 412 inside the eye has a radial component of the magnetic induction (Br). The interaction between the induced current (I) and the radial component of the magnetic induction (Br) generates the electromagnetic force (Fem)

[0102] FIGs. 6A and 6B 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.

[0103] Referring to FIG. 7, shown is a flowchart 700 depicting steps of a method of measuring an internal pressure value of an eye, in accordance with an embodiment of the present disclosure. At step 702, a cornea of an eye is oscillated by providing a variable magnetic field. At step 704, a frequency of the variable magnetic field is varied in a predefined range of frequency. At step 706, at least a peak amplitude value of an oscillation of the cornea of the eye is measured. At step 708, a lowest value of the frequency corresponding to the peak amplitude value is found to find a resonance frequency value of the cornea of the eye. At step 710, the internal pressure value of the eye is calculated using the resonance frequency.

[0104] The steps 702, 704, 706, 708, and 710 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.

[0105] Modifications to embodiments of the present disclosure described in the foregoing are possible without departing from the scope of the present disclosure as defined by the accompanying claims. Expressions such as "including", "comprising", "incorporating", "have", "is" used to describe and claim the present disclosure are intended to be construed in a nonexclusive manner, namely allowing for items, components or elements not explicitly described also to be present. Reference to the singular is also to be construed to relate to the plural.

Claims

CLAIMS1. A non-contact tonometer (100, 200, 302, 502) comprising:- an excitation and measuring unit (102, 202, 300, 504) comprising- an electromagnetic exciter (104, 204, 306, 400, 506) comprising- at least one electric coil (106, 206, 304, 404, 508) powered with a variable current (i) and arranged to generate a variable magnetic field (416, 500),- at least one magnetic armature (108, 208, 210, 212, 510) arranged to guide the variable-magnetic field towards an eye (110, 214, 303, 418, 512) for at least partially passing through a cornea (112, 216, 301, 402) of the eye.

2. A non-contact tonometer (100, 200, 302, 502) according to claim 1, wherein the electromagnetic exciter (104, 204, 306, 400, 506) further comprises at least one permanent magnet (218, 220, 316, 412).

3. A non-contact tonometer (100, 200, 302, 502) according to claims 1 or 2, wherein the excitation and measuring unit (102, 202, 300, 504) further comprises an optical displacement sensor (114, 222, 320).

4. A non-contact tonometer (100, 200, 302, 502) according to claim 3, wherein the optical displacement sensor (114, 222, 320) is selected to be at least one of a confocal chromatic displacement sensor, a laser doppler vibrometer.

5. A non-contact tonometer (100, 200, 302, 502) according to claim 4, wherein the confocal chromatic displacement sensor is operable to measure with a beam of infrared light.

6. A non-contact tonometer (100, 200, 302, 502) according to any of the claim 3 to 5, wherein the optical displacement sensor (114, 222, 320) is operable to measure at least one of selected from:- an amplitude of oscillation of at least one point of the cornea (112, 216, 301, 402),- a thickness of the cornea in at least one point;- a distance between the cornea and the excitation and measuring unit (102, 202, 300, 504).

7. A non-contact tonometer (100, 200, 302, 502) according to any of the preceding claims, wherein the at least one magnetic armature (108, 208, 510) is an U-shaped magnetic armature having a first arm (116) with a first end and a second arm (118) with a second end.

8. A non-contact tonometer (100, 200, 302, 502) according to claim 7, wherein the optical displacement sensor (114, 222, 320) is arranged between the first arm (116) and the second arm (118).

9. A non-contact tonometer (100, 200, 302, 502) according to claims 7 or 8, wherein a distance between the first arm (116) and the second arm (118) is decreasing towards the first end and the second end.

10. A non-contact tonometer (100, 200, 302, 502) according to any of the claims 2 to 6, wherein- the permanent magnet (218, 220, 304, 412) has a substantially annular shape, with a first pole and a second pole on the opposite faces;- the electromagnetic exciter (104, 204, 306, 400, 506) has a proximal end (308) and a distal end (310), the electromagnetic exciter further comprises a volume of space extending along a center line of the electromagnetic exciter from the proximal end until the distal end; and- the at least one magnetic armature (108, 208, 210, 212, 510) comprising- an internal magnetic armature (312, 406) arranged to surround at least partially the volume of space and to be magnetically coupled with the first pole of the permanent magnet via the second end,- an external magnetic armature (314, 408) arranged to surround at least partially the electric coil (106, 206, 316, 404, 508) and being magnetically coupled to the second pole of the permanent magnet; and wherein- the electric coil is arranged to at least partially surround the internal magnetic armature.

11. A non-contact tonometer (100, 200, 302, 502) according to claim 10, wherein the optical displacement sensor (114, 222, 320) is arranged inside the volume of space.

12. A method of measuring an internal pressure value of an eye (110, 214, 303, 418, 512), the method comprising:- oscillating a cornea (112, 216, 301, 402) of the eye by providing a variable magnetic field (416, 500),- varying a frequency of the variable magnetic field in a predefined range of frequency,- measuring at least a peak amplitude value of an oscillation of the cornea of the eye,- finding a lowest value of the frequency corresponding to a peak amplitude value to find a resonance frequency value of the cornea of the eye, and- calculating the internal pressure value of the eye using the resonance frequency.

13. A method according to claim 12, wherein the variable magnetic field (416, 500) is produced by a coil powered with a variable current (i) and a frequency scan of the variable current is performed over a frequency range.

14. A method according to claims 12 or 13, further comprising- measuring a thickness of a cornea (112, 216, 301, 402) of the eye (110, 214, 303, 418, 512) in at least one point;- measuring a resonance frequency value of the cornea; and- calculating the internal pressure value of the eye using both the value of the resonance frequency of the cornea and the value of the thickness of the cornea.

15. A method according to claims 12 to 14, further comprising- measuring a distance value between the cornea (112, 216, 301, 402) and an excitation and measuring unit (102, 202, 300, 504), and - using the measured distance value as a feedback signal to place the excitation and measuring unit at a desired position relative to the cornea.

16. A method according to any of the claims from 13 to 15, wherein an electrical impedance of the coil is continuously measured during frequency scanning of the variable current (i) and wherein the resonance frequency value is the lowest frequency of the current (i) that causes a peak amplitude value of the electrical impedance of the coil.

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