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

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.

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).

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.

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.

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.