Noninvasive methods and apparatuses for measuring the intraocular pressure of a mammal eye

• US 6,673,014 B2
• Filed: 10/05/2001
• Issued: 01/06/2004
• Est. Priority Date: 10/05/2001
• Status: Expired due to Fees

• Current Assignee: iTONIX, Inc.
• Original Assignee: iTONIX, Inc.
• Inventors: Badehi, Avner Pierre, Klein, Raphael, Glazer, Arieh
• Primary Examiner(s): Hindenburg, Max F.
• Assistant Examiner(s): FOREMAN, JONATHAN M
• Application Number:
  US09/972,819
• Publication Number:
  US 20030078486A1
• Time in Patent Office: 823 Days
• Field of Search: 73/80, 600/399, 600/400, 600/401, 600/402, 600/403, 600/404, 600/405, 600/561
• US Class Current: 600/398
• CPC Class Codes: A61B 3/165 Non-contacting tonometers
• CPC Class Codes: A61B 8/10 Eye inspection

Abstract

Noninvasive methods and apparatuses measuring the intraocular pressure (IOP) of the eye using vibratory excitation are disclosed. Prior art methods teaches that the natural frequencies of the eye vary as a function of the IOP, with each natural frequency being zero at zero IOP. The present invention recognizes that the eye has different and separate classes of natural frequencies that vary as function of the IOP, which have non-zero values for a zero value of IOP, and which have curves that extrapolate to negative IOPs to obtain zero values of frequency. Preferred methods and apparatuses of the present invention measure a first natural frequency of this class at an unknown IOP value, and thereafter compare it to one or more known values of the first natural frequency measured at corresponding known IOPs to estimate value of the unknown IOP. Preferred embodiments include measuring one or more additional natural frequencies.

Claims

1. A method of estimating the intraocular pressure of an eye of a mammal with a gaseous environment around a portion of its surface, the gaseous environment having a pressure, the intraocular pressure being the difference between the pressure inside the eye and the pressure of the gaseous environment, said method comprising the steps of:

(a) measuring a first frequency value of a first vibratory frequency of the eye at a portion of the sclera or cornea of the eye at an unknown intraocular pressure, said first vibratory frequency being associated with a corresponding first vibratory mode of the eye and having a value which varies as a first function of the eye'"'"'s intraocular pressure, the first function having form which extends or extrapolates to a non-zero frequency value for a zero value of intraocular pressure and to a zero frequency value for a negative value of intraocular pressure; and

(b) comparing the first measured frequency value to one or more known frequency values of the first vibratory frequency measured at corresponding known intraocular pressures to estimate value of the unknown intraocular pressure.

2. The method of claim 1 further comprising the steps of:

(c) measuring a second frequency value of a second vibratory frequency of the eye at the portion of sclera or cornea of the eye at the unknown intraocular pressure value, said second vibratory frequency being associated with a corresponding second vibratory mode of the sclera and having a value which varies as a second function of the eye'"'"'s intraocular pressure, the second function having form which extends or extrapolates to a non-zero frequency value for a zero value of intraocular pressure and to a zero frequency value for a negative value of intraocular pressure; and

wherein step (b) comprises the step of comparing the first and second measured frequency values measured at the unknown intraocular pressure to the one or more known values of the first vibratory frequency, to the known intraocular pressures corresponding thereto, and to one or more known values of the second vibratory frequency measured at corresponding known intraocular pressures to estimate value of the unknown intraocular pressure.

3. The method of claim 2 wherein step (a) comprises the steps of:

applying a plurality of vibrations at a plurality of frequencies to the eye, at least some of the vibrations causing one or more portions of the eye'"'"'s surface to undergo an oscillatory motion;

measuring the phase of the vibratory motion of a portion of the eye'"'"'s surface relative to the applied vibrations; and

selecting the first measured vibratory frequency as a first frequency of the applied vibrations at which the measured phase of the vibratory motion lags the phase of the applied vibrations by approximately 90 or 270 degrees; and

wherein step (c) comprises the steps of;

applying a plurality of vibrations at a plurality of frequencies to the eye, at least some of the vibrations causing one or more portions of the eye'"'"'s surface to undergo an oscillatory motion;

measuring the phase of the vibratory motion of a portion of the eye'"'"'s surface relative to the applied vibrations; and

selecting the second measured vibratory frequency as a second frequency of the applied vibrations at which the measured phase of the vibratory motion lags the phase of the applied vibrations by approximately 90 or 270 degrees.

4. The method of claim 2 wherein the first measured vibratory frequency and the second measured vibratory frequency differ from one other by at least 50 Hz.

5. The method of claim 1 wherein step (a) comprising the steps of:

applying a plurality of vibrations at a plurality of frequencies to the eye, at least some of the vibrations causing one or more portions of the eye'"'"'s surface to undergo an oscillatory motion;

measuring the phase of the vibratory motion of a portion of the eye'"'"'s surface relative to the applied vibrations; and

selecting the first measured vibratory frequency as a first frequency of the applied vibrations at which the measured phase of the vibratory motion lags the phase of the applied vibrations by approximately 90 or 270 degrees.

6. The method of claim 1 wherein step (b) comprises the step of comparing the first measured frequency value to a first known value of the first vibratory frequency measured at a corresponding first known intraocular pressure and outputing an indication that the unknown pressure is above the first known intraocular pressure when the first measured frequency value is greater than the known value of the first vibratory frequency, and outputing an indication that the unknown pressure is below the first known intraocular pressure when the first measured frequency value is less than the known value of the first vibratory frequency.

7. The method of claim 1 wherein step (b) comprises the steps of:

computing a frequency difference between the first measured frequency value and a first known value of the first vibratory frequency measured at a corresponding first known intraocular pressure;

generating a pressure differential by multiplying the difference by a pre-computed factor which relates changes in intraocular pressure to changes in frequency value; and

generating the estimate of the unknown intraocular pressure as the first known intraocular pressure plus the pressure differential.

8. The method of claim 1 wherein step (b) comprises the steps of:

computing a squared-frequency difference between the square of the first measured frequency value and the square of a first known value of the first vibratory frequency measured at a corresponding first known intraocular pressure;

generating a pressure differential multiplying the squared-frequency difference by a pre-computed factor which relates changes in intraocular pressure to changes in squared frequency values; and

generating the estimate of the unknown intraocular pressure as the first known intraocular pressure plus the pressure differential.

9. The method of claim 1 wherein step (b) comprises the steps of:

forming a mathematical relationship for the first vibratory mode which is mathematically equivalent to;

10. The method of claim 9 wherein the constants A₀ and A₁ are generated from a first measurement f_1,1 of the first vibratory frequency measured at a first known intraocular pressure Δ

p₁ and a second measurement f_2,1 of the first vibratory frequency measured at a second intraocular pressure Δ

p₂ according to forms which are mathematically equivalent to;

11. The method of claim 1 wherein step (a) comprises the step of measuring at least a portion of a first frequency spectrum of the measured portion of the eye, the portion including the first vibratory frequency, and wherein step (b) comprises the step of correlating the portion of the first frequency spectrum to a portion of a second frequency spectrum of the measured portion of the eye measured at a known value intraocular pressure and including the first vibratory frequency.

12. The method of claim 11 wherein the step of correlating comprises the steps of generating Fourier transforms of the portions of frequency spectrums.

13. A method of estimating the intraocular pressure of an eye of a mammal within a gaseous environment around a portion of the eye, the gaseous environment having a pressure, the intraocular pressure being the difference between the pressure inside the eye and the pressure of the gaseous environment, said method comprising the steps of:

(a) measuring a first vibratory frequency and a second vibratory frequency of an eye at an unknown intraocular pressure which is to be estimated to generate a first measured vibratory frequency and a second measured vibratory frequency, respectively;

(b) generating a first implied pressure value of the unknown intraocular pressure by comparing the first measured vibratory frequency to one or more measured values of a first previously-measured vibratory frequency measured at one or more corresponding known intraocular pressures;

(c) generating a second implied pressure value of the unknown intraocular pressure by comparing the second measured vibratory frequency to one or more measured values of a second previously-measured vibratory frequency measured at one or more corresponding known intraocular pressures;

(d) generating a third implied pressure value of the unknown intraocular pressure by comparing the first measured vibratory frequency to one or more measured values of the second previously-measured vibratory frequency;

(e) generating a fourth implied pressure value of the unknown intraocular pressure by comparing the second measured vibratory frequency to one or more measured values of a third previously-measured vibratory frequency measured at one or more corresponding known intraocular pressures;

(f) generating a first estimated pressure from the first and second implied pressure values as an average thereof, and generating a first deviation value representative of a deviation of the first and second implied pressure values from the first estimated pressure;

(g) generating a second estimated pressure from the third and fourth implied pressure values as an average thereof, and generating a second deviation value representative of a deviation of the third and fourth implied pressure values from the second estimated pressure; and

wherein each of the vibratory frequencies has a value which varies as a respective function of the eye'"'"'s intraocular pressure, each respective function extending or extrapolating to a non-zero frequency value for a zero value of intraocular pressure and to a zero frequency value for a negative value of intraocular pressure.

14. The method of claim 13 further comprising the step of selecting the first estimated pressure as a final estimated pressure if the first deviation value is less than the second deviation value, and the step of selecting the second estimated pressure as a final estimated pressure if the second deviation value is less than the first deviation value.

15. The method of claim 13 wherein the function of the first previously-measured vibratory frequency comprises a first mathematical relationship which provides an output pressure value for a corresponding input frequency value, wherein the function of the second previously-measured vibratory frequency comprises a second mathematical relationship which provides an output pressure value for a corresponding input frequency value, and wherein the function of the third previously-measured vibratory frequency comprises a third mathematical relationship which provides an output pressure value for a corresponding input frequency value;

wherein the step (b) of generating the first implied pressure value comprises evaluating the first mathematical relationship by providing the first measured vibratory frequency as the input frequency value of the first relationship and setting the first implied pressure value equal to the output pressure value of the first relationship, the first mathematical relationship being previously generated from at least the one or more values of the first previously-measured vibratory frequency;

wherein the step (c) of generating the second implied pressure value comprises evaluating the second mathematical relationship by providing the second measured vibratory frequency as the input frequency value of the second relationship and setting the second implied pressure value equal to the output pressure value of the second relationship, the second mathematical relationship being previously generated from at least the one or more values of the second previously-measured vibratory frequency;

wherein the step (d) of generating the third implied pressure value comprises evaluating the second mathematical relationship by providing the first measured vibratory frequency as the input frequency value of the second relationship and setting the third implied pressure value equal to the output pressure value of the second relationship; and

wherein the step (e) of generating the fourth implied pressure value comprises evaluating the third mathematical relationship by providing the second measured vibratory frequency as the input frequency value of the third relationship and setting the fourth implied pressure value equal to the output pressure value of the third relationship, the third mathematical relationship being previously generated from at least the one or more values of the third previously-measured vibratory frequency.

16. The method of claim 15 wherein the mathematical relationships may be identified and distinguished with respect to one another by an index value n, wherein the n-th mathematical relationship comprises a form which is mathematically equivalent to:

17. The method of claim 16 wherein the constants A_0,n and A_1,n of an n-th relationship of a corresponding previously-measured vibratory frequency are generated from a first measurement f_1,n of the corresponding vibratory frequency measured at a first known intraocular pressure Δ

p₁ and a second measurement f_2,n of the corresponding vibratory frequency measured at a second intraocular pressure Δ

p₂ according to forms which are mathematically equivalent to;

18. The method of claim 13 wherein step (a) comprising the steps of:

applying a plurality of vibrations at a plurality of frequencies to the eye, at least some of the vibrations causing one or more portions of the eye'"'"'s surface to undergo an oscillatory motion;

measuring the phase of the vibratory motion of a portion of the eye'"'"'s surface relative to the applied vibrations;

selecting the first measured vibratory frequency as a first frequency of the applied vibrations at which the measured phase of the vibratory motion lags the phase of the applied vibrations by approximately 90 or 270 degrees; and

selecting the second measured vibratory frequency as a second frequency of the applied vibrations at which the measured phase of the vibratory motion lags the phase of the applied vibrations by approximately 90 or 270 degrees.

19. The method of claim 13 wherein the first measured vibratory frequency and the second measured vibratory frequency differ from one another by at least 50 Hz.

20. A method of estimating the intraocular pressure of an eye of a mammal within a gaseous environment around a portion of its surface, the gaseous environment having a pressure, the intraocular pressure being the difference between the pressure inside the eye and the pressure of the gaseous environment, said method comprising the steps of:

(a) measuring, at an unknown intraocular pressure which is to be estimated, a plurality of vibratory frequencies of an eye to generate a plurality of measured vibratory frequencies;

(b) making an assignment of a selected number of the measured vibratory frequencies to corresponding selected ones of a plurality of mathematical relationships, each mathematical relationship being associated with a corresponding vibratory mode and corresponding vibratory frequency and providing an output pressure value for a corresponding input frequency value, each mathematical relationship being previously generated from at least one or more measured values of the corresponding vibratory frequency measured at one or more known intraocular pressures;

(c) computing a plurality of implied pressure values for the unknown intraocular pressure value, each implied pressure value being generated by providing the measured vibratory frequency previously assigned to the mathematical relationship as the input frequency value of the relationship and setting the implied pressure value equal to the output pressure value of the relationship; and

(d) generating an average of the implied pressure values generated by step (c).

21. The method of claim 20 wherein step (d) further comprises the step of generating a corresponding deviation representative a deviation of the implied pressure values from the average;

and

wherein the method further comprises the step of repeating steps (b) through (d) one or more times, each time with a different assignment of measured vibratory frequencies, and generating the estimate for the unknown intraocular pressure as the average computed by step (d) which has the smallest corresponding deviation value.

22. The method of claim 20 wherein the mathematical relationships may be identified and distinguished with respect to one another by an index value n, wherein the n-th mathematical relationship comprises a form which is mathematically equivalent to:

23. The method of claim 22 wherein the constants A_0,n and A_1,n of an n-th relationship are generated from a first measurement f_1,n of the corresponding vibratory frequency measured at a first known intraocular pressure Δ

p₁ and a second measurement f_2,n of the corresponding vibratory frequency measured at a second intraocular pressure Δ

p₂ according to forms which are mathematically equivalent to;

24. The method of claim 20 wherein step (a) comprising the steps of:

applying a plurality of vibrations at a plurality of frequencies to the eye, at least some of the vibrations causing one or more portions of the eye'"'"'s surface to undergo an oscillatory motion;

measuring the phase of the vibratory motion of a portion of the eye'"'"'s surface relative to the applied vibrations;

selecting two or more frequencies of the applied vibrations at which the measured phase of the vibratory motion lags the phase of the applied vibrations by approximately 90 or 270 degrees, each selected frequency being designated as a measured vibratory frequency.

25. The method of claim 20 wherein each of the measured vibratory frequencies differs from each of the other measured vibratory frequencies by at least 50 Hz.

26. The method of claim 20 wherein each of the vibratory frequencies has a value which varies as a respective function of the eye'"'"'s intraocular pressure, each respective function extending or extrapolating to a non-zero frequency value for a zero value of intraocular pressure and to a zero frequency value for a negative value of intraocular pressure.

27. A method of measuring the intraocular pressure of a patient'"'"'s eye with a first tonometer, the first tonometer having a model which estimates the pressure of an eye as a function of a set of one or more vibratory frequencies of the eye and a plurality of data parameters, the first tonometer having a first memory for storing the data parameters of the model, an ability to measure the patient'"'"'s eye to obtain a set of one or more measured vibratory frequencies of one or more corresponding vibratory modes of the patient'"'"'s eye, and an ability to provide a set of measured vibratory frequencies to the model to estimate the corresponding pressure of the eye, said method comprising the steps of:

(a) measuring the intraocular pressure of the patient'"'"'s eye at a first time with a second tonometer that is different from the first tonometer, the measured pressure being designated as the first pressure;

(b) measuring the intraocular pressure of the patient'"'"'s eye at a second time with the second tonometer or with a third tonometer that is different from the first tonometer, the measured pressure being designated as the second pressure and being different from the first pressure by an amount of three or more millimeters of Mercury;

(c) measuring the patient'"'"'s eye with the first tonometer to obtain a first set of one or more measured vibratory frequencies of one or more corresponding vibratory modes, the measuring step being done at a time that is closer to the first time than the second time;

(d) measuring the patient'"'"'s eye with the first tonometer to obtain a second set of one or more measured vibratory frequencies of said corresponding one or more vibratory modes, the measuring step being done at a time that is closer to the second time than the first time; and

(e) storing in the first memory a set of data parameters that is representative of the known intraocular pressures and the measured vibratory frequencies at the known intraocular pressures.

28. The method of claim 27 further comprising the steps of:

(f) measuring the patient'"'"'s eye with the first tonometer to obtain a third set of one or more measured vibratory frequencies of said corresponding vibratory modes at an unknown intraocular pressure; and

(g) inputting the third set of one or more measured vibratory frequencies to the model to estimate the corresponding pressure of the patient'"'"'s eye.

29. The method of claim 27 wherein step (e) comprises the step of computing at least one of the data parameters of the first tonometer'"'"'s model from the first set of measured vibratory frequencies, the second set of measured vibratory frequencies, the first pressure, and the second pressure prior to storing said at least one of the data parameters in the first memory.

30. The method of claim 27 wherein step (e) comprises storing one of the intraocular pressures as one of the data parameters in the first memory.

31. The method of claim 27 wherein step (e) comprises storing one or more of the measured vibratory frequencies as one or more corresponding data parameters in the first memory.

32. The method of claim 27 wherein step (e) comprises storing one or more squared measured vibratory frequencies as one or more corresponding data parameters in the first memory.

33. The method of claim 27 wherein the corresponding vibratory modes of the first set of measure vibratory frequencies are the same as the corresponding vibratory modes of the second set of measured vibratory frequencies.

34. A method of measuring the intraocular pressure of a patient'"'"'s eye with a first tonometer, the first tonometer having a model which estimates the pressure of an eye as a function of a set of two or more vibratory frequencies of the eye and a plurality of data parameters, the first tonometer further having a first memory for storing the data parameters of the model, an ability to measure the patient'"'"'s eye to obtain a set of two or more vibratory frequencies of one or more corresponding vibratory modes of the patient'"'"'s eye, and an ability to provide a set of vibratory frequencies to the model to estimate the corresponding pressure of the eye, said method comprising the steps of:

(a) directing the patient to have the intraocular pressure of his or her eye measured at a first time with a second tonometer which is different from the first tonometer, the measured pressure being designated as the first pressure;

(b) directing the patient to have the intraocular pressure of his or her eye measured at a second time with the second tonometer or with a third tonometer that is different from the first tonometer, the measured pressure being designated as the second pressure and being different from the first pressure by an amount of three (3) or more millimeters of Mercury;

(c) directing the patient to have his or her eye measured with the first tonometer to obtain a first set of vibratory frequencies of one or more corresponding vibratory modes, the measurement being done at a time which is closer to the first time than the second time;

(d) directing the patient to have his or her eye measured with the first tonometer to obtain a second set of vibratory frequencies of said corresponding one or more vibratory modes, the measurement being done at a time which is closer to the second time than the first time;

(e) providing a processor to generate the parameters of the first tonometer'"'"'s model from the first set of vibratory frequencies, the second set of vibratory frequencies, the first pressure, and the second pressure;

(f) directing the patient to have the first and second pressures provided to the processor; and

(g) directing the processor to generate the parameters of the first tonometer'"'"'s model and to provide the generated parameters in the first memory.

35. The method of claim 34 further comprising the steps of:

(h) directing the patient to have his or her eye measured with the first tonometer to obtain a third set of vibratory frequencies; and

(i) directing a processor within the first tonometer to estimate the pressure corresponding to the third set of vibratory frequencies from the tonometer'"'"'s model and the third set of vibratory frequencies.

36. The method of claim 34 wherein the processor is external to the first tonometer.

37. The method of claim 34 wherein the processor is internal to the first tonometer and has a human interface that receives the values of the first and second pressures.

38. The method of claim 34 wherein step (g) generates one of the data parameters as the first pressure.

39. The method of claim 34 wherein step (g) generates one or more of the data parameters as one or more corresponding vibratory frequencies of the first set of vibratory frequencies.

40. A tonometer which measures the intraocular pressure of an eye of a mammal within a gaseous environment around a portion of its surface, the gaseous environment having a pressure, the intraocular pressure being the difference between the pressure inside the eye and the pressure of the gaseous environment, said tonometer comprising:

a processor having a first memory and a second memory;

a controllable frequency generator having a control input coupled to the processor and an output;

a vibratory exciter having an electric input coupled to the output of frequency generator and an output which delivers vibrations to the eye;

a displacement detector which detects vibratory displacements of a surface area of the eye, said displacement detector having an electrical output which provides a signal representative of the vibratory displacements;

a phase detector having a first input which receives a signal related to the output of the controlled frequency generator, a second input coupled to the electrical output of the displacement detector, and an output coupled to processor which provides a value related to the phase difference between the signals at the detector'"'"'s first and second inputs;

a model of the pressure of the eye based on one or more vibratory frequencies of the eye, the model comprising a first set of instructions stored in said first memory, and a set of data parameters stored in said second memory for each vibratory frequency, the first set of instructions operating on the corresponding data parameters of a vibratory frequency to generate a pressure value as a function of the parameters and an input frequency value, each said function corresponding to a vibratory frequency and having form which extends or extrapolates to a non-zero frequency value for a zero value of intraocular pressure and to a zero frequency value for a negative value of intraocular pressure;

a second set of instructions stored in the first memory that directs the processor to command the controlled frequency generator to output a plurality of waveforms at a plurality of different frequencies;

a third set of instructions which directs the processor to monitor the output of the phase detector and to detect one or more vibratory frequencies therefrom; and

a fourth set of instructions stored in the first memory that directs the processor to compute an estimated pressure from a set of detected vibratory frequencies and the model, the fourth set directing the processor to execute the first set of instructions using at least one set of stored parameters.

41. The tonometer of claims 40 wherein the function of each vibratory mode has a form which is mathematically equivalent to:

42. The tonomoeter of claim 41 wherein the parameters of the model are derived from a first set (f_1,k) of vibratory frequencies measured at a first known pressure level of the eye and a second set (f_2,k) of vibratory frequencies measured at a second known and different pressure level of the eye from mathematical forms equivalent to:

43. The tonometer of claim 40 further comprising a pressure chamber adapted to be fit over at least a portion of the upper face of a patient to provide a gaseous environment around the eye which can be varied, wherein the exciter and displacement detector are disposed within the chamber.

44. The tonometer of claim 43 further comprising a compressor pump having an output coupled to sealed chamber.

45. The tonometer of claim 43 further comprising a vacuum pump having an output coupled to sealed chamber.

46. The tonometer of claim 41 wherein the first memory comprises a nonvolatile memory, and wherein the parameters A_0,n and A_1,n are computed and stored in the first memory, and thereafter called from the first memory as needed in computing a plurality of estimated pressure values.

47. The tonomoter of claim 40 wherein each of the vibratory frequencies is greater than 50 Hz.

48. The tonometer of claim 41 wherein the second memory comprises a nonvolatile memory, wherein the data parameters stored therein comprise the first and second sets of vibratory frequencies and the first and second known pressures, and wherein the first set of instructions comprising a subset of instructions which direct the processor to compute the parameters A_0,n and A_1,n as needed from the data stored in the non-volatile memory.

49. The tonometer of claim 40 wherein the displacement detector comprises an ultrasonic emitter and an ultrasonic detector.

50. The tonometer of claim 40 wherein the vibratory exciter comprises an acoustical speaker.

51. The tonometer of claim 40 wherein output of the frequency generator is swept in either the ascending direction or descending direction, up to a value of 4000 Hz.