Method and apparatus for examining an eye

• US 20030236470A1
• Filed: 06/25/2002
• Published: 12/25/2003
• Est. Priority Date: 06/25/2002
• Status: Active Grant

• Current Assignee: FALCK, FRANCIS Y. AND ROBERT T. FALCK
• Original Assignee: FALCK, FRANCIS Y. AND ROBERT T. FALCK
• Inventors: Falck, Robert W., Falck, Francis Y. Jr.
• Granted Patent: US 7,473,231 B2
• Time in Patent Office: Days
• US Class Current: 600/558
• CPC Class Codes: A61B 3/16 for measuring intraocular pressure, e.g. tonometers
• CPC Class Codes: A61B 5/02216 Ophthalmodynamometers

Abstract

An applanation tonometer and its operation involve an actuator pressing a prism with a variable and determinable force against a cornea of an eye while a source directs light to reflect from an applanation surface of the prism to a detector producing a detected light signal received by a microprocessor. Such a tonometer produces a diastolic phase signal and a systolic phase signal representing the complete intra ocular pressure experience of the eye being examined. The signal information allows combined diastolic and systolic IOP to be determined in several corroborating ways and also yields measures of ocular blood flow and tonography.

Claims

1. A method of measuring intra ocular pressure (IOP) of an eye, the method using a tonometer having an actuator pressing a prism with a variable and determinable force against a cornea of the eye while a source directs light to reflect from an applanation surface of the prism to a detector producing a detected light signal received by a microprocessor, the method comprising:

a. programming the microprocessor to recognize a preliminary value of the detected light signal occurring upon preliminary contact of the applanation surface with the cornea, the preliminary value varying from one eye to another based on specific corneal thickness and curvature of the eye being examined;

b. operating the actuator to press the prism applanation surface against the cornea with increasing force applied during a time interval to change the detected light signal from the preliminary value through a range of values extending from the preliminary value; and

c. programming the microprocessor to determine IOP from changes in the detected light signal corresponding to prism pressure force changes in the range of values so that the IOP calculation is substantially unaffected by thickness and curvature of the cornea of the eye being examined.

2. The method of measuring IOP of claim 1 including programming the microprocessor to determine IOP from the prism pressure force required to change the detected light signal to an end value in the range of values that is farthest from the preliminary value.

3. The method of measuring IOP of claim 2 including programming the microprocessor to determine a slope of the detected light signal change in the range of values and using the slope to corroborate the IOP determination.

4. The method of measuring IOP of claim 2 including programming the microprocessor to determine the total time required to change the detected light signal from the preliminary value to the end value and using the total time to corroborate the determined IOP.

5. The method of measuring IOP of claim 1 including programming the microprocessor to determine IOP from a slope of the detected light signal change in the range of values.

6. The method of measuring IOP of claim 1 including programming the microprocessor to determine IOP from a slope of the detected light signal change in the range of values, the prism pressure force required to change the detected light signal to an end value in the range of values that is farthest from the preliminary value, and by the time required to change the detected light signal through the range of values.

7. The method of measuring IOP of claim 1 including operating the actuator to increase the prism pressing force in predetermined increments of force applied in respective predetermined increments of time.

8. The method of measuring IOP of claim 1 including programming the microprocessor to hold the applanation surface against the cornea long enough for at least two systolic pulses to occur and to determine ocular pulse pressure from changes occurring in the detected light signal during the systolic pulses.

9. The method of measuring IOP of claim 8 including programming the microprocessor to determine a mean or average IOP based on pulse rate, the ocular pulse pressure, and a diastolic IOP unaffected by ocular pulse pressure.

10. The method of measuring IOP of claim 1 wherein the IOP determined from changes in the detected light signal in the range of values is a diastolic IOP, and including programming the microprocessor to determine ocular pulse pressure from a departure of the detected light signal from the diastolic IOP during a systolic pulse.

11. The method of measuring IOP of claim 10 including allowing at least two systolic pulses to occur while the actuator presses the applanation surface against the cornea, and programming the microprocessor to determine pulse rate and an effective IOP based on both the diastolic IOP and the ocular pulse pressure.

12. The method of measuring IOP of claim 10 including programming the microprocessor to determine ocular blood flow from the extent of the change occurring in the detected light signal during the systolic pulse.

13. The method of measuring IOP of claim 10 including programming the microprocessor to determine tonography based on a rate of change of the detected light signal from the systolic pulse back to a diastolic state.

14. A tonometer arranged to operate by the method of claim 1.

15. A tonometer arranged to operate by the method of claim 8.

16. A tonometer arranged to operate by the method of claim 10.

17. A method of measuring intra ocular pressure (IOP) of an eye, the method using a tonometer having an actuator pressing a prism with a variable and determinable force against a cornea of the eye while a source directs light to reflect from an applanation surface of the prism to a detector producing a detected light signal received by a microprocessor, the method comprising:

a. programming the microprocessor to determine a diastolic IOP based on a relationship between the detected light signal and changes in the prism pressing force applied by the actuator;

b. operating the actuator to hold the prism against the cornea with a predetermined force for a long enough duration for two systolic pulses to occur; and

c. programming the microprocessor to determine ocular pulse pressure from departures of the detected light signal from the diastolic IOP during the systolic pulses.

18. The method of measuring IOP of claim 17 including programming the microprocessor to determine a pulse rate and an effective IOP based on both the diastolic IOP and the ocular pulse pressure.

19. The method of measuring IOP of claim 17 including programming the microprocessor to determine ocular blood flow from the departure of the detected light signal from the diastolic IOP during the systolic pulses.

20. The method of measuring IOP of claim 17 including programming the microprocessor to determine a tonography measure by using the detected light signal change from a systolic pulse pressure to a diastolic state.

21. A tonometer arranged to operate by the method of claim 17.

22. A tonometer arranged to operate by the method of claim 19.

23. A tonometer arranged to operate by the method of claim 20.

24. A method of measuring ocular blood flow of an eye, the method using a tonometer having an actuator pressing a prism with a variable and determinable force against a cornea of the eye while a source directs light to reflect from an applanation surface of the prism to a detector producing a detected light signal received by a microprocessor, the method comprising:

a. operating the tonometer to determine a diastolic intra ocular pressure (IOP) from the detected light signal occurring during absence of systolic pulses;

b. operating the actuator to hold the prism against the cornea for a long enough duration for a systolic pulse to occur; and

c. programming the microprocessor to determine ocular blood flow from a departure of the detected light signal from the diastolic IOP during the systolic pulse.

25. The method of claim 24 including operating the actuator to hold the prism against the cornea for a long enough duration for two systolic pulses to occur.

26. A tonometer arranged to operate by the method of claim 24.

27. A method of measuring tonography of an eye, the method using a tonometer having an actuator pressing a prism with a variable and determinable force against a cornea of the eye while a source directs light to reflect from an applanation surface of the prism to a detector producing a detected light signal received by a microprocessor, the method comprising:

a. the microprocessor being programmed to determine from the detected light signal a diastolic intra ocular pressure (IOP) and an ocular pulse pressure; and

b. the microprocessor being programmed to determine tonography based on a return of the detected light signal from an ocular pulse pressure value occurring during a systolic pulse to a diastolic value occurring during absence of a systolic pulse.

28. The method of claim 27 including the microprocessor being programmed to determine ocular blood flow based on differences between the ocular pulse pressure and the diastolic IOP.

29. A tonometer arranged to operate by the method of claim 27.

30. A tonometer having an actuator pressing a prism with a variable and determinable force against a cornea of an eye while a source directs light to reflect from an applanation surface of the prism to a detector producing a detected light signal received by a microprocessor, the tonometer comprising:

a. the microprocessor being programmed to determine an intra ocular pressure (IOP) based on both the detected light signal received during a diastolic phase and the detected light signal received during a systolic pulse;

b. the microprocessor being programmed to hold the prism against the cornea of the eye for a long enough duration for two systolic pulses to occur, and

c. the microprocessor being programmed to determine from the detected light signal an average or mean IOP based on a diastolic IOP, a systolic IOP, and a pulse rate.

31. The tonometer of claim 30 wherein the microprocessor is programmed to determine ocular blood flow from departures of the detected light signal from the diastolic IOP during the systolic pulses.

32. The tonometer of claim 30 wherein the microprocessor is programmed to determine tonography based on a return of the detected light signal from a systolic value occurring during a systolic pulse to a diastolic value occurring during absence of a systolic pulse.

33. A tonometer comprising:

a. a prism having an applanation surface arranged to be pressed against a cornea of an eye being examined, the prism being supported on a rotationally moveable arm;

b. an electromagnetic actuator arranged for pressing the prism against the cornea with a predetermined and variable force;

c. the electromagnetic actuator including a permanent magnet and a coil one of which is mounted on the arm supporting the prism and the other of which is mounted in a fixed position;

d. a counterbalance applying a rotational moment arm to return the prism arm to a starting position without requiring a return spring;

e. a source directing light into the prism to reflect from the applanation surface to a detector; and

f. a microprocessor arranged to receive a detected light signal from the detector and being programmed to determine an intra ocular pressure (IOP) of the eye based on changes in the detected light signal in response to variable electromotive force from the actuator pressing the prism with corresponding variable force against the cornea.

34. The tonometer of claim 33 wherein the prism is replaceable, and the microprocessor is programmed to require replacement of the prism after the prism has been used for examining a pair of eyes of a patient.

35. A method of measuring tonography of an eye, the method using a tonometer having an actuator pressing a prism with a variable and determinable force against a cornea of the eye while a source directs light to reflect from an applanation surface of the prism to a detector producing a detected light signal received by a microprocessor, the method comprising:

a. programming the microprocessor to determine from the detected light signal a preceding intra ocular pressure (IOP) of the eye;

b. programming the microprocessor to press the prism against the eye with sufficient force to raise the IOP of the eye to a level above the preceding IOP for a predetermined brief interval after determining the preceding IOP;

c. programming the microprocessor to release the prism pressure force against the eye at the end of the predetermined interval and to then determine from the detected light signal a subsequent IOP of the eye; and

d. programming the microprocessor to determine a tonography measurement from the difference between the preceding and subsequent IOP determinations.

36. The tonometer of claim 35 wherein the force of pressing the prism against the eye for the predetermined interval is sufficient to depress an ocular pulse signal during the predetermined interval.

37. A tonometer arranged to operate by the method of claim 35.

38. A method of treating an eye for glaucoma, the method using a tonometer producing an intra ocular pressure (IOP) determination and a tonography determination, and the method comprising:

a. treating the eye with a drug aimed at reducing production of aqueous fluid if the IOP determination is high enough to warrant treatment and the tonography determination is normal; and

b. treating the eye with a drug aimed at improving performance of a trabecular meshwork of the eye if the IOP determination is high enough to warrant treatment and the tonography determination is subnormal.

39. A method of treating an eye for glaucoma, the method using a tonometer producing an intra ocular pressure (IOP) determination, and an ocular blood flow determination, and the method comprising:

if the IOP determination is high enough to warrant treatment, and if the ocular blood flow determination is below normal, then treating the eye with a drug aimed at reducing IOP without reducing ocular blood flow.

40. The method of claim 39 including using the tonometer to redetermine IOP and ocular blood flow after treatment, and changing the drug if ocular blood flow has reduced.

41. The method of claim 39 including using the tonometer to redetermine IOP and ocular blood flow after treatment, and treating the eye with an additional drug aimed at improving ocular blood flow if ocular blood flow has reduced.

42. A method of treating an eye for normal pressure glaucoma, the method using a tonometer producing an intra ocular pressure (IOP) determination, and an ocular blood flow determination, and the method comprising:

if the IOP determination is normal and if the ocular blood flow determination is below normal, then treating the patient with a drug aimed at increasing ocular blood flow.

43. The method of claim 42 including using the tonometer to redetermine IOP and ocular blood flow after treatment to verify that the drug has increased ocular blood flow.