SYSTEMS AND METHODS FOR EFFICIENTLY OBTAINING MEASUREMENTS OF THE HUMAN EYE USING TRACKING

• US 20120249956A1
• Filed: 03/28/2012
• Published: 10/04/2012
• Est. Priority Date: 03/30/2011
• Status: Active Grant

• Current Assignee: Carl Zeiss Meditec Incorporated (Carl-Zeiss-Stiftung)
• Original Assignee: Carl Zeiss Meditec Incorporated (Carl-Zeiss-Stiftung)
• Inventors: NARASIMHA-IYER, Harihar, Everett, Matthew J.
• Granted Patent: US 9,033,510 B2
• Time in Patent Office: Days
• US Class Current: 351/206
• CPC Class Codes: A61B 3/0025 characterised by electronic signal processing, e.g. eye models
• CPC Class Codes: A61B 3/0033 characterised by user input arrangements
• CPC Class Codes: A61B 3/102 for optical coherence tomography [OCT]
• CPC Class Codes: A61B 3/113 for determining or recording eye movement
• CPC Class Codes: A61B 3/12 for looking at the eye fundus, e.g. ophthalmoscopes A61B3/13 takes precedence
• CPC Class Codes: A61B 3/145 by video means
• CPC Class Codes: A61B 5/0066 Optical coherence imaging
• CPC Class Codes: G06T 2207/10101 Optical tomography; Optical coherence tomography [OCT]
• CPC Class Codes: G06T 2207/20081 Training; Learning
• CPC Class Codes: G06T 2207/30041 Eye; Retina; Ophthalmic
• CPC Class Codes: G06T 2210/41 Medical
• CPC Class Codes: G06T 7/246 using feature-based methods, e.g. the tracking of corners or segments

Abstract

Systems and methods for efficiently obtaining optical coherence tomography (OCT) measurement data with reduced effects of motion are presented. One embodiment involves determining the amount of motion present during the collection of an OCT data set based on images of the eye collected at the same time as the OCT data, and recollecting select portions of the OCT data set when the amount of eye motion is determined to exceed a predetermined threshold. Another embodiment includes enabling or disabling a tracking feature based on the quality of the images available for tracking. Another embodiment includes reducing the effect of motion in the axial direction based on a comparison to a model of the eye constructed from OCT data. The method can also be used to reduce the presence of mirror image artifacts in an OCT image.

Claims

1. A method for reducing the effects of motion in measurement data from the eye of a patient, said method comprising:

collecting measurement data at a plurality of positions across the eye of the patient using a measurement system;

simultaneously collecting images of the retina of the patient such that each measurement has a corresponding image frame using a fundus imaging system different from the measurement system;

comparing each image frame to a reference image frame to determine the amount of eye movement that occurred during the collection of the measurement data;

collecting replacement measurement data when the determined amount of eye movement associated with one or more positions exceeds a predetermined threshold, with the location of the collected replacement measurement data being adjusted to compensate for the determined amount of eye movement;

generating an image from the measurement data; and

storing or displaying the image.

2. A method as recited in claim 1, wherein the measurement data is collected using an optical coherence tomography system.

3. A method as recited in claim 2, wherein measurement data is continued to be collected while the image frames are being compared to determine whether to collect replacement measurement data.

4. A method as recited in claim 2, where the measurement data is collected across the retina of the eye of the patient.

5. A method as recited in claim 2, further comprising assessing the quality of each image frame prior to the comparing step.

6. A method as recited in claim 5, further comprising using an image frame as the reference frame for future comparisons if the quality of the image frame exceeds the quality of the reference frame.

7. A method as recited in claim 5, wherein the quality of the image frame is assessed by analyzing one or both of:

the intensity of the image or the focus of the image.

8. A method as recited in claim 5, further comprising disabling the comparing and collecting steps if the quality of the image frames fall below a predetermined threshold.

9. A method as recited in claim 2, further comprising assessing the quality of the image frames to determine the reference frame and enable the comparing and collecting replacement data steps.

10. A method as recited in claim 2, further comprising displaying an indicator of the quality of the image frames to the user.

11. A method as recited in claim 2, further comprising using an image frame as the reference frame for subsequent measurements if a significant eye movement is detected.

12. A method as recited in claim 2, wherein the images of the retina are collected using a line-scan imager.

13. A method as recited in claim 2, wherein the images of the retina are collected using a confocal scanning laser ophthalmoscope.

14. A method as recited in claim 2, wherein the predetermined threshold is defined by the user.

15. A method as recited in claim 2, wherein the predetermined threshold is different at different locations on the eye.

16. A method as recited in claim 2, wherein the predetermined threshold is varied depending on the measurement acquisition time.

17. A method as recited in claim 2, further comprising completing the remainder of the measurements without collecting new replacement data if the total acquisition time exceeds a predetermined amount of time.

18. A method as recited in claim 2, further comprising comparing image frames from subsequent measurements in addition to the image frame at a particular position in determining whether to collect replacement measurement data at a particular position.

19. A method as recited in claim 2, wherein the comparing is done based on features apparent in the image frame and the reference image frame.

20. A method as recited in claim 19, wherein the best features selected for the comparison are adaptively learned.

21. A method as recited in claim 5, further comprising displaying an indication of the quality of the image frames to the user.

22. A method as recited in claim 2, wherein the reference image was collected on the patient from a prior examination or visit.

23. A method as recited in claim 2, further comprising:

comparing a reference frame collected at a previous visit to a reference frame collected at the current visit;

using the correspondence between the reference frame from the current visit and the image frames to determine the plurality of positions to be scanned such that the resulting OCT measurement data is collected at the same positions as a set of OCT measurement data collected at a previous visit.

24. A method as recited in claim 2, wherein the comparison is carried out on portions of the image and reference frames.

25. A method for reducing the effects of axial motion in optical coherence tomography (OCT) data from the eye of a patient, said method comprising:

establishing a predefined range of acceptable axial locations based on features or landmarks present in OCT data;

collecting OCT measurement data at a plurality of positions across the eye of the patient using an OCT system;

analyzing features in the collected OCT data to determine if the collected OCT data falls within the predefined range of axial locations to determine axial motion;

collecting replacement OCT data where the axial location is not within the predefined acceptable axial range, with the location of the collected replacement OCT data being adjusted to compensate for the determined axial motion;

generating an image from the measurement data; and

storing or displaying the image.

26. A method as recited in claim 25, wherein the adjustment is achieved by changing the pathlength of one arm of the OCT system.

27. A method as recited in claim 25, wherein the range of acceptable axial locations is determined using a model of the eye.

28. A method as recited in claim 27, wherein the model of the eye is created using three or more B-scans.

29. A method as recited in claim 27, wherein the model of the eye is created using one or more of:

the top location of the tissue, the bottom location of the tissue, and the centroid location of the tissue.

30. A method as recited in claim 28, wherein the model is created from data taken at a previous examination of the patient.

31. A method as recited in claim 25, wherein the OCT data is collected on the anterior region of the eye.

32. A method as recited in claim 25, wherein the OCT data is collected on the retina of the eye.

33. A system for acquiring reduced motion measurement data comprising:

a measurement system for collecting measurement data at a plurality of positions across the retina of a patient;

an imaging system for collecting images of the retina of the patient, such that each measurement has a corresponding image frame;

a processor for comparing each image frame to a reference image frame to determine eye movement and for controlling the measurement system to collect new replacement measurement data at a particular position if the eye movement at that position determined by said comparison exceeds a predetermined threshold.

34. A system as recited in claim 33, wherein the measurement system is an optical coherence tomography (OCT) system.

35. A system as recited in claim 34, wherein the OCT system continues to collect measurement data while the processor determines if it is necessary to collect replacement measurement data.

36. A system as recited in claim 34, wherein prior to comparing the image frame to a reference frame, the processor assesses the quality of the image frame.

37. A system as recited in claim 36, further comprising a display for displaying an indication of the image quality of the user.

38. A system as recited in claim 33, wherein the predetermined threshold is established by the user.

39. A method for eliminating minor images in OCT measurement data from the eye of a patient, said method comprising:

collecting OCT measurement data at a plurality of positions across the eye of the patient;

determining a characteristic metric for the OCT measurement data based upon the intensity gradients in the axial and lateral dimensions of the data;

collecting replacement OCT measurement data when the metric exceeds a predetermined value;

generating an OCT image from the measurement data; and

storing or displaying the image.

40. A method as recited in claim 39, wherein the predetermined value is determined from a collection of OCT data.

41. A method for reducing the effects of motion in OCT measurement data from the eye of a patient, said method comprising:

collecting a first set of OCT measurement data at a plurality of locations across the eye of a patient in a time period short enough so that motion of the eye in the axial direction is minimized;

establishing a model of the eye using the first set of OCT measurement data that reflects the curvature and axial location of features within the measurement data;

collecting a second set of OCT measurement data at a plurality of locations across the eye of a patient using an OCT measurement system, wherein the number of locations in the second set is greater than the number of locations in the first set;

comparing the curvature and axial locations of features of the second set of OCT measurement data to the curvature and axial locations of the features in the model to determine the amount of eye motion that occurred during the collection of the second set of OCT measurement data;

collecting replacement OCT measurement data when the determined amount of eye movement exceeds a predetermined threshold;

generating an image from the measurement data; and

storing or displaying the image.

42. A method as recited in claim 41, wherein the method is used to remove mirror image artifacts from the OCT measurement data.