Apparatus, System and Method for Precision Depth Measurement

• US 20100130966A1
• Filed: 11/21/2008
• Published: 05/27/2010
• Est. Priority Date: 11/21/2008
• Status: Active Grant

• Current Assignee: Advanced Medical Optics Incorporated (Johnson & Johnson), AMO Development LLC (Johnson & Johnson)
• Original Assignee: Advanced Medical Optics Incorporated (Johnson & Johnson)
• Inventors: Brownell, Michael
• Granted Patent: US 8,852,175 B2
• Time in Patent Office: Days
• US Class Current: 606/4
• CPC Class Codes: A61B 3/1005 for measuring distances inside the eye, e.g. thickness of the cornea A61B3/11 takes precedence
• CPC Class Codes: A61B 3/107 for determining the shape or measuring the curvature of the cornea
• CPC Class Codes: A61F 2009/00872 Cornea
• CPC Class Codes: A61F 2009/00897 Scanning mechanisms or algorithms
• CPC Class Codes: A61F 9/008 using laser

Abstract

Systems, apparatus, and methods are disclosed for locating tissue layer transitions within a cornea, including focusing a laser to a laser spot with an energy below a photodisruption threshold of the cornea, varying a position of the focal spot of the laser between an anterior surface of the cornea and a posterior surface of the cornea, and determining one or more transitions of the tissue layers based on a change in harmonic light generated by the laser spot.

Claims

1. A method of locating tissue layers within a cornea, the cornea having an anterior surface, a posterior surface, and a photodisruption threshold, the method comprising the steps of:

focusing a laser beam to a laser spot having an energy below the photodisruption threshold of the cornea, the laser beam having a pre-determined wavelength;

varying a position of the laser spot between the anterior surface of the cornea and the posterior surface of the cornea, a harmonic signal based on the pre-determined wavelength being produced as the laser spot propagates in the cornea; and

determining a transition of the tissue layers based on a predetermined change in the harmonic signal.

2. The method of claim 1, further comprising generating the laser beam from a femtosecond laser.

3. The method of claim 2, wherein the harmonic of the pre-determined wavelength has an intensity correlated with a density of the cornea, and wherein the determining step comprises determining a transition of the tissue layers based on a change in the intensity of the harmonic signal.

4. The method of claim 1, further comprising determining a depth measurement from the anterior surface of the cornea or the posterior surface of the cornea based on the transition of tissue layers.

5. The method of claim 1, further comprising determining a thickness between a first tissue layer of the tissue layers and a second tissue layer of the tissue layers based on the transition of the tissue layers.

6. The method of claim 1, wherein the tissue layers comprise one or more of the group consisting of an epithelium, a Bowman'"'"'s layer, a stroma, a Descemet'"'"'s membrane, and an endothelium.

7. The method of claim 1, wherein the varying step comprises continuously varying a position of the laser spot between the anterior surface of the cornea and the posterior surface of the cornea.

8. The method of claim 1, wherein the varying step comprises varying a position of the laser spot in increments between the anterior surface of the cornea and the posterior surface of the cornea.

9. The method of claim 1, further comprising determining multiple transitions of the tissue layers at various locations across the cornea.

10. The method of claim 1, further comprising generating a three dimensional model of the tissue layers.

11. The method of claim 1, further comprising aplanating the cornea prior to determining the transition of tissue layers.

12. The method of claim 1, further comprising calibrating a focal depth of the laser spot based on the transition of the tissue layers.

13. A system for locating tissue layer transitions within a cornea having an anterior surface, a posterior surface, and a photodisruption threshold, the system comprising:

a laser subsystem configured to scan a laser spot between the anterior surface of the cornea and the posterior surface of the cornea, the laser spot having an energy below the photodisruption threshold, a harmonic signal being produced as the laser spot propagates in the cornea;

a sensor configured to detect the harmonic signal; and

a processor coupled to the sensor and the laser subsystem, the processor configured to;

monitor a location of the laser spot within the cornea;

measure a predetermined change in the harmonic signal; and

correlate the location of the laser spot within the cornea with the change in the harmonic signal to determine a tissue layer transition within the cornea.

14. The system of claim 13, wherein the cornea has adjacent tissue layers with different harmonic signals;

and wherein the predetermined change in the harmonic signal indicates the tissue layer transition.

15. The system of claim 14, wherein the tissue layers comprise one or more of the group consisting of an epithelium, a Bowman'"'"'s layer, a stroma, a Descemet'"'"'s membrane, and an endothelium.

16. The system of claim 14, wherein the processor is further configured to determine a distance between the tissue layer transition and the anterior surface of the cornea or the posterior surface of the cornea.

17. The system of claim 14, wherein the processor is further configured to determine a thickness of the tissue layers based on the harmonic signal.

18. The system of claim 13, wherein the laser subsystem comprises a femtosecond laser.

19. The system of claim 14, wherein the harmonic signal has an intensity;

and wherein the predetermined change is based on a predetermined change in the intensity of the harmonic signal.

20. The system of claim 13, wherein the processor is further configured to generate a three dimensional model of the tissue layers based on the tissue layer transition.

21. The system of claim 13, wherein the laser subsystem is further configured to:

output a pulsed incision beam having a pulse energy of greater than or equal to the photodisruption threshold; and

incise the cornea with the pulsed incision beam based on the tissue layer transition.

22. An apparatus for determining a depth measurement and incising a cornea, the cornea having a photodisruption threshold, the apparatus comprising:

a first input operable to receive a first input signal indicating a focal depth of a laser beam within the cornea, the laser beam having an energy below the photodisruption threshold;

a second input operable to receive a second input signal representing a harmonic of the laser beam generated as the laser beam propagates in the cornea;

an output; and

a processor coupled to the first input, the second input, and the output, the processor configured to;

detect a pre-determined change in the second input signal, the pre-determined change indicating a tissue layer interface within the cornea;

correlate the focal depth of the laser beam with the tissue layer transition to provide a reference depth of the laser beam; and

transmit an output signal via the output, the output signal indicating the reference depth of the laser beam.

23. The apparatus of claim 22, wherein the cornea has a Bowman'"'"'s layer, a stroma, and an epithelium, and wherein the processor is further configured to:

determine a first tissue layer transition between the Bowman'"'"'s layer and the stroma based on a first pre-determined change in the second input signal; and

determine a second tissue layer transition between the Bowman'"'"'s layer and the epithelium based on a second pre-determined change in the second input signal.

24. The apparatus of claim 22, wherein the cornea has an anterior surface and a posterior surface, and wherein the processor is further configured to determine a distance from an anterior surface of the cornea to the tissue layer transition.

25. The apparatus of claim 24, wherein the cornea has a stroma, and wherein the processor is further configured to determine an incision depth of the laser beam based on the tissue layer transition, the incision depth being within the stroma.

26. The apparatus of claim 24, wherein the processor is further configured to:

determine multiple tissue layer transitions in the cornea based by detecting different pre-determined changes in the second input signal; and

generate a three dimensional model based on the multiple tissue layer transitions.