Apparatus and method for measuring intraocular pressure

• US 20020177768A1
• Filed: 04/08/2002
• Published: 11/28/2002
• Est. Priority Date: 08/21/2000
• Status: Active Grant

• Current Assignee: Cleveland Clinic Foundation
• Original Assignee: Cleveland Clinic Foundation
• Inventors: Fleischman, Aaron J., Roy, Shuvo
• Granted Patent: US 6,994,672 B2
• Time in Patent Office: Days
• US Class Current: 600/406
• CPC Class Codes: A61B 2562/0247 Pressure sensors
• CPC Class Codes: A61B 3/16 for measuring intraocular pressure, e.g. tonometers

Abstract

An apparatus (176) for measuring intraocular pressure (IOP) comprises an applanation tonometer (180) having a distal end that is movable toward the eye and a disposable module (188) positioned at the distal end. The module (188) includes a sensor carrier (192) and a sensor (10) connected to the sensor carrier. The sensor (10) comprises a contact surface (14) for making contact with a surface portion of the eye (36). The contact surface (14) includes an outer non-compliant region (16) and an inner compliant region (18) fabricated as an impedance element that varies in impedance as the inner compliant region changes shape. The sensor (10) further comprises a region of conductive material (38) electrically coupled to the impedance element of the compliant region (18) and responsive to an external signal for energizing the impedance element so that the IOP may be determined.

Claims

1. An apparatus for measuring intraocular pressure of an eye, said apparatus comprising:

an applanation tonometer having a distal end that is movable toward the eye; and

a disposable module positioned at said distal end of said applanation tonometer, said module including a sensor carrier and a sensor connected to said sensor carrier, said sensor comprising;

a contact surface for making contact with a surface portion of the eye, said contact surface including an outer non-compliant region and an inner compliant region fabricated as an impedance element that varies in impedance as said inner compliant region changes shape; and

a region of conductive material electrically coupled to said impedance element of said compliant region and responsive to an external signal for energizing said impedance element so that the intraocular pressure may be determined.

2. The apparatus of claim 1 wherein said sensor is comprised of silicon material.

3. The apparatus of claim 1 wherein said sensor is comprised of a polymeric material.

4. The apparatus of claim 3 wherein said sensor comprises at least two layers of polymeric film bonded together.

5. The apparatus of claim 1 wherein said compliant region comprises a diaphragm that functions as one plate of a capacitive element, said diaphragm being separated by a dielectric region from another plate of said capacitive element, said diaphragm flexing closer to said other plate as said contact surface is pressed against the surface portion of the eye to change the capacitance of said capacitive element in proportion to the intraocular pressure of the eye.

6. The apparatus of claim 5 wherein said dielectric region comprises air.

7. The apparatus of claim 5 wherein said dielectric region comprises hydrogel.

8. The apparatus of claim 5 wherein said dielectric region comprises silicone.

9. The apparatus of claim 5 wherein said region of conductive material comprises an inductor coil that is electrically coupled to said capacitive element to form a resonant circuit, the external signal comprising an electromagnetic signal that varies in frequency to cause said resonant circuit to be energized and resonant at a frequency in proportion to the capacitance of said capacitive element so that the intraocular pressure may be determined.

10. The apparatus of claim 9 wherein said inductor coil is fabricated in said non-compliant region.

11. The apparatus of claim 9 wherein said inductor coil is fabricated on said inner compliant region.

12. The apparatus of claim 11 further comprising a second inductor coil formed underneath said diaphragm.

13. The apparatus of claim 9 wherein said inductor coil is formed by disposing conductive material in a predetermined pattern in a surface of said non-compliant region about said compliant region of said contact surface.

14. The apparatus of claim 1 further comprising an antenna at said distal end of said applanation tonometer, said antenna for transmitting the external signal for energizing said impedance element.

15. The apparatus of claim 14 further comprising a control unit for generating the external signal to measure a signal representative of intraocular pressure, said control unit being operatively coupled with said antenna.

16. The apparatus of claim 15 wherein said compliant region comprises a capacitive element that changes capacitance in proportion to its change in shape, said region of conductive material comprising an inductive coil electrically coupled to said capacitive element to form a resonant circuit.

17. The apparatus of claim 16 wherein said means for generating an external signal generates an electromagnetic signal that varies over a predetermined frequency range to cause said resonant circuit to resonate, said control unit including means for measuring the resonant frequency of said resonant circuit which is representative of the intraocular pressure of the eye.

18. The apparatus of claim 15 wherein said control unit includes processing means for measuring signals representative of intraocular pressure at different times during a predetermined time interval, and a memory for storing the measured signals representative of the intraocular pressure measured at said different times.

19. The apparatus of claim 18 wherein said control unit includes means for processing the stored measured signals representative of intraocular pressure to determine a resultant intraocular pressure (IOP) measurement.

20. The apparatus of claim 19 wherein said control unit includes means for time marking each resultant IOP measurement with a measurement time and for storing said resultant IOP measurements with their corresponding measurement times in the memory.

21. The apparatus of claim 20 wherein said control unit includes means for transferring the stored resultant IOP measurements and their corresponding measurement times to another system.

22. The apparatus of claim 15 wherein said control unit includes a display for displaying the intraocular pressure measurements.

23. The apparatus of claim 1 wherein said sensor further comprises a region of material responsive to a non-invasive external force to press said contact surface against the surface portion of the eye and cause said inner compliant region to change shape in proportion to the intraocular pressure.

24. The apparatus of claim 23 wherein said region of material responsive to a non-invasive external force comprises a magnetic material responsive to a magnetic field, the strength of said magnetic field determining the external force at which said contact surface is pressed against the surface portion of the eye.

25. The apparatus of claim 24 further comprising a control unit for generating a non-invasive force over a predetermined time interval and for generating said external signal to measure a signal representative of intraocular pressure.

26. The apparatus of claim 25 wherein said control unit includes means for generating a magnetic field as said non-invasive external force.

27. The apparatus of claim 26 wherein said control unit includes means for generating said external signal superimposed on said magnetic field.

28. The apparatus of claim 1 wherein said sensor is bonded to said sensor carrier.

29. The apparatus of claim 1 wherein said sensor is connected by spring means to said sensor carrier.

30. A method for measuring intraocular pressure (IOP) of an eye, said method comprising the steps of:

providing an applanation tonometer with a distal end that is movable toward the eye;

positioning a disposable module at the distal end of the applanation tonometer, the module including a sensor carrier and a sensor connected to the carrier, the sensor having a compliant region that functions as an impedance element;

moving the distal end of the applanation tonometer until the sensor comes into contact with a surface portion of the eye which causes the compliant region to change shape and vary in impedance;

energizing the impedance element;

determining a representative pressure measurement each time the impedance element is energized; and

processing the representative pressure measurements to render a resultant IOP measurement.

31. The method of claim 30 wherein said step of energizing the impedance element includes the step of:

energizing an inductive region of the sensor that is connected to the impedance element which is a capacitive region to cause a circuit formed by the regions to resonate.

32. The method of claim 31 wherein said step of energizing an inductive region of the sensor includes transmitting an activation signal over an antenna.

33. The method of claim 31 wherein said step of energizing the impedance element includes generating an electromagnetic signal with a frequency that is swept through a frequency range over a predetermined time interval, the resonant frequency of the circuit falling within said frequency range.

34. The method of claim 33 wherein said step of determining includes the steps of determining the resonant frequency of the circuit each time the circuit is energized, the resonant frequencies sampled being representative of the IOP of the eye at different times.

35. The method of claim 34 wherein said step of processing includes processing the sampled data resonant frequencies to render a resultant IOP measurement.

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

time marking each resultant IOP measurement; and

storing each IOP measurement along with its corresponding measurement time.

37. The method of claim 36 further comprising the step of transmitting the stored IOP measurements and their corresponding measurement times to an external site.

38. The method of claim 37 wherein said steps of energizing, determining and processing are performed autonomously by a control unit.

39. The method of claim 38 further comprising the step of displaying the resultant IOP measurement on the control unit.

40. The method of claim 39 further comprising the step of displaying the resultant IOP measurement.

41. The method of claim 30 wherein said step of moving the distal end of the applanation tonometer includes the step of generating a non-invasive force which presses the compliant region against the surface portion of the eye in accordance with a predetermined force vs. time envelope.

42. The method of claim 41 wherein said step of energizing the impedance element is performed multiple times during the force vs. time envelope.

43. The method of claim 41 wherein said step of generating a non-invasive force includes the steps of:

generating a magnetic field in accordance with a magnetic field strength vs. time envelope; and

causing a permanent magnet region on the sensor to press the compliant region against the surface portion of the eye.

44. The method of claim 41 wherein said step of energizing the impedance element includes generating an electromagnetic signal that energizes the impedance element, the electromagnetic signal being superimposed on the magnetic field that causes the permanent magnet region on the sensor to press the compliant region against the surface portion of the eye.