High speed tracking of IOL during refractive index modification
During a process of refractive index modification of an intraocular lens (IOL) using an ophthalmic laser system, optical position monitoring of the IOL is performed by a video camera system viewing the top surface of the IOL. Fiducials are incorporated into the IOL at manufacture, or created in-vivo with laser. The monitoring method employs a defined area of interest (AOI) to limit the number of pixels to be analyzed, to achieve adequately high acquisition speed. In one example, the AOI contains 5 camera scan line segments, each line segment having sufficient pixels to create a stable amplitude signature. Successive frames of the AOI are analyzed to detect movement of the fiducial and/or to determine whether the fiducial has been lost.
1. A process of modifying an intraocular lens (IOL) implanted in a patient's eye using an ophthalmic laser system, comprising:
delivering a laser beam into the IOL to modify a refractive property of the IOL;
simultaneously monitoring a position of the IOL within the eye, which includes:
operating a video camera to acquire an image of a field of view containing the IOL;
performing a contrast analysis on the image to locate a high contrast fiducial of the IOL, the fiducial being located away from an edge of the IOL;
obtaining a reference area of interest (AOI) from the image, the reference AOI being centered around the fiducial and containing a predefined number of video camera scan line segments with a predefined number of pixels per scan line segment, a size of the reference AOI being smaller than a size of the IOL as defined by an outline of the edge of the IOL;
operating the video camera to obtain multiple successive AOIs from successive images, each AOI containing the predefined number of video camera scan line segments with the predefined number of pixels per scan line segment; and
analyzing each of the multiple successive AOIs, without analyzing any image portions of the successive images other than the AOI, to determine a direction and magnitude of movement of the fiducial; and
controlling delivery of the laser beam into the IOL based on the direction and/or magnitude of movement of the fiducial.
2. The method of claim 1 , wherein the predefined number of video camera scan line segments in each AOI is 5 and the predefined number of pixels per scan line segment is 20.
3. The method of claim 1 , wherein the step of analyzing each AOI includes comparing, by using a least squares fit, each scan line segment of the AOI with each scan line segment of the reference AOI or of a previous one of the AOIs, to obtain a best-fitting pair of scan line segments in the two AOIs which indicates the direction and magnitude of movement.
4. The method of claim 1 , wherein the simultaneously monitoring step further includes:
after determining the direction and magnitude of movement of the fiducial by analyzing each AOI, adjusting a position of a next AOI based on the determined direction and magnitude of movement before obtaining the next AOI.
5. The method of claim 1 , wherein the controlling step includes: when the magnitude of movement of the fiducial determined in the analyzing step is greater than a predetermined movement threshold, pausing delivery of the laser beam into the IOL.
6. The method of claim 1 , wherein the simultaneously monitoring step further includes, for each of at least some of the multiple AOIs:
comparing a peak to valley difference value of the AOI with a peak to valley difference value of the reference AOI or of a previous one of the AOIs; and
when the peak to valley difference value of the AOI is smaller than the peak to valley difference value of the reference AOI or the previous AOI by more than a predetermined threshold, re-performing the steps of operating the video camera to acquire an image of a field of view containing the IOL, performing a contrast analysis on the image to locate a high contrast fiducial of the IOL, and obtaining a reference AOI from the image centered around the fiducial.
7. The method of claim 1 , wherein the simultaneously monitoring step further includes, for each of at least some of the multiple AOIs: comparing a peak to valley difference value of the AOI with a peak to valley difference value of the reference AOI or of a previous one of the AOIs; and
wherein the controlling step further includes: when the peak to valley difference value of the AOI is smaller than the peak to valley difference value of the reference AOI or the previous AOI by more than a predetermined threshold, pausing delivery of the laser beam into the IOL.
8. The method of claim 1 , wherein the step of operating the video camera to obtain multiple successive AOIs includes, for each AOI:
operating the camera to read out data from an entire detector array of the camera; and
defining an area of the read-out data at a defined location containing the predefined number of scan line segments with the predefined number of pixels per scan line segment as the AOI.
9. The method of claim 1 , wherein the step of operating the video camera to obtain multiple successive AOIs includes, for each AOI:
operating the camera to read out only a portion of a detector array of the camera as the AOI, the portion being located at a defined location and having the predefined number of scan line segments with the predefined number of pixels per scan line segment.
10. The method of claim 1 , wherein the step of operating the video camera to obtain multiple successive AOIs includes, for each AOI:
operating the camera to read out only a portion of a detector array of the camera, the portion being located at a first defined location and having more scan line segments than the predefined number of scan line segments with more pixels per scan line segment than the predefined number of pixels per scan line segment; and
defining an area of the read-out data at a second defined location containing the predefined number of scan line segments with the predefined number of pixels per scan line segment as the AOI.
11. The method of claim 1 , wherein the step of operating the video camera to obtain multiple successive AOIs and the step of analyzing each of the multiple successive AOIs are performed at a rate of over 1 kHz.
12. An ophthalmic surgical laser system for modifying an intraocular lens (IOL) implanted in a patient's eye, the system comprising:
a laser light source configured to generate a laser beam;
an optical delivery system configured to deliver the laser beam to the IOL, including a scanner system configured to scan the laser beam within the IOL;
a video camera configured to acquire an image of a field of view containing the IOL; and
a controller configured to control the laser light source and the scanner system to deliver the laser beam in the IOL to modify a refractive property of the IOL, the controller being programmed to simultaneously monitor a position of the IOL within the eye, including:
to operate the video camera to acquire an image of a field of view containing the IOL;
to perform a contrast analysis on the image to locate a high contrast fiducial of the IOL, the fiducial being located away from an edge of the IOL;
to obtain a reference area of interest (AOI) from the image, the reference AOI being centered around the fiducial and containing a predefined number of video camera scan line segments with a predefined number of pixels per scan line segment, a size of the reference AOI being smaller than a size of the IOL as defined by an outline of the edge of the IOL;
to operate the video camera to obtain multiple successive AOIs from successive images, each AOI containing the predefined number of video camera scan line segments with the predefined number of pixels per scan line segment; and
to analyze each of the multiple successive AOIs, without analyzing any image portions of the successive images other than the AOI, to determine a direction and magnitude of movement of the fiducial; and
wherein the controller is further configured to control delivery of the laser beam into the IOL based on the direction and/or magnitude of movement of the fiducial.
13. The ophthalmic surgical laser system of claim 12 , wherein the predefined number of video camera scan line segments in each AOI is 5 and the predefined number of pixels per scan line segment is 20.
14. The ophthalmic surgical laser system of claim 12 , wherein the step of analyzing each AOI includes comparing, by using a least squares fit, each scan line segment of the AOI with each scan line segment of the reference AOI or of a previous one of the AOIs, to obtain a best-fitting pair of lines scan line segments in the two AOIs which indicates the direction and magnitude of movement.
15. The ophthalmic surgical laser system of claim 12 , wherein the controller is further programed to:
after determining the direction and magnitude of movement of the fiducial by analyzing each AOI, adjust a position of a next AOI based on the determined direction and magnitude of movement before obtaining the next AOI.
16. The ophthalmic surgical laser system of claim 12 , wherein the controller is further programed to:
when the magnitude of movement of the fiducial determined in the analyzing step is greater than a predetermined movement threshold, pause delivery of the laser beam into the IOL.
17. The ophthalmic surgical laser system of claim 12 , wherein the controller is further programed to, for each of at least some of the multiple AOIs:
compare a peak to valley difference value of the AOI with a peak to valley difference value of the reference AOI or of a previous one of the AOIs; and
when the peak to valley difference value of the AOI is smaller than the peak to valley difference value of the reference AOI or the previous AOI by more than a predetermined threshold, re-perform the steps of operating the video camera to acquire an image of a field of view containing the IOL, performing a contrast analysis on the image to locate a high contrast fiducial of the IOL, and obtaining a reference AOI from the image centered around the fiducial.
18. The ophthalmic surgical laser system of claim 12 , wherein the controller is further programed to, for each of at least some of the multiple AOIs:
compare a peak to valley difference value of the AOI with a peak to valley difference value of the reference AOI or of a previous one of the AOIs; and
when the peak to valley difference value of the AOI is smaller than the peak to valley difference value of the reference AOI or the previous AOI by more than a predetermined threshold, pause delivery of the laser beam into the IOL.
19. The ophthalmic surgical laser system of claim 12 , wherein the controller is programed to, when obtaining each AOI:
operate the camera to read out data from an entire detector array of the camera; and
define an area of the read-out data at a defined location containing the predefined number of scan line segments with the predefined number of pixels per scan line segment as the AOI.
20. The ophthalmic surgical laser system of claim 12 , wherein the controller is programed to, when obtaining each AOI:
operate the camera to read out only a portion of a detector array of the camera as the AOI, the portion being located at a defined location and having the predefined number of scan line segments with the predefined number of pixels per scan line segment.
21. The ophthalmic surgical laser system of claim 12 , wherein the controller is programed to, when obtaining each AOI:
operate the camera to read out only a portion of a detector array of the camera, the portion being located at a first defined location and having more scan line segments than the predefined number of scan line segments with more pixels per scan line segment than the predefined number of pixels per scan line segment; and
define an area of the read-out data at a second defined location containing the predefined number of scan line segments with the predefined number of pixels per scan line segment as the AOI.
22. The ophthalmic surgical laser system of claim 12 , wherein the controller is programed to perform the step of operating the video camera to obtain multiple successive AOIs and the step of analyzing each of the multiple successive AOIs are performed at a rate of over 1 kHz.