Abstract:
The field of the invention relates to systems and methods for eye imaging and, more particularly, for balancing illuminations in eye imaging. An asymmetric illumination method to compensate for the imbalance illumination caused by nose reflection is described. In one embodiment, a method for balancing illuminations in eye imaging comprises generating one or more eye images, using the images to detect the imbalance illuminations from the nasal sclera and temporal sclera with the selected region of interest. In another embodiment, a system for balancing illuminations in eye imaging uses the detected imbalance illumination ratio of nasal/temporal sclera as the signal for adjusting the brightness of the infrared LEDs for asymmetric illumination.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of priority to U.S. Provisional Patent Application Ser. No. 61/745,080 filed on Dec. 21, 2012, the entire disclosure of which is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to eye imaging and, more particularly, to balancing infrared illuminations in eye imaging. 
     BACKGROUND OF THE INVENTION 
     Current ophthalmic diagnostic and measurement systems typically use wavefront acquisition and diagnostic capabilities to deliver measurement accuracy, thereby enhancing the precision of laser vision correction surgery. An exemplary ophthalmic diagnostic and measurement product using wavefront is the Abbott WaveScan WaveFront System, which, among having other capabilities and technologies, uses a Shack-Hartmann wavefront sensor that can quantify aberrations throughout the entire optical system of the patient&#39;s eye, including second-order aberrations related to spherical error and cylindrical errors, and higher-order aberrations related to coma, trefoil, and spherical aberrations. An exemplary wavefront diagnostic system was described in U.S. Pat. No. 7,931,371 to Dai, and is herein incorporated by reference in its entirety. 
     In addition to its use in ophthalmic diagnostic and measurement systems, laser technology has become the technique of choice for ophthalmic surgical applications, such as refractive surgery for correcting myopia, hyperopia, astigmatism, and so on, as well as procedures for treating and removing a cataractous lens. Known laser-assisted ophthalmic surgical systems typically use a variety of forms of lasers and/or laser energy to effect vision correction, including infrared lasers, ultraviolet lasers, picosecond lasers, femtosecond lasers, wavelength multiplied solid-state lasers, and the like. Laser-assisted ophthalmic surgical systems often also use wavefront diagnostic systems to accurately measure the refractive characteristics of a particular patient&#39;s eye. 
     A wavefront diagnostic system generally captures eye images during wavefront measurement. A pupil camera in an aberrometer captures images of the eye, illuminated by infrared light-emitting diodes (LEDs) designed as a symmetric configuration. These eye images are used, for example, for iris registration for laser vision correction. Eye images from the diagnostic system, however, often show the sclera on the nasal side as appearing brighter than the sclera on the temporal side. This is true for both the right eye and the left eye. The eye image is essential for wavefront-guided corneal refractive surgery since it identifies the treatment area and is used for eye tracking. The pupil itself is not a reliable marker for the treatment area because its size and center change depending on the lighting condition or administered medication. The outer iris boundary (OIB), a circular boundary between the iris and the sclera of the eye, however, is fixed. The aberrometer thus identifies this boundary from the eye image for the iris registration for laser vision correction. But, most eye images captured by the pupil camera show that the sclera on the nasal side looks brighter than the sclera on the temporal side, both from the right eye (OD) and the left eye (OS). This imbalance illumination is typically caused by secondary reflections of infrared LEDs by the patient&#39;s nose.  FIG. 1  shows typical eye images, captured during wavefront measurement where the pupil illumination uses infrared LEDs. The image shows the sclera on the nasal side appearing brighter than the sclera on the temporal side for both the right eye (OD) and the left eye (OS). The imbalance illumination can cause failure in detecting the OIB, and as such, it is desirable to correct it in the diagnostic system for laser-assisted ophthalmic surgery. 
     Accordingly, improved systems and methods for balancing infrared illuminations in eye imaging are desirable. 
     SUMMARY OF THE INVENTION 
     The field of the invention generally relates to systems and methods for eye imaging and, more particularly, for correcting the imbalance illumination caused by nose reflections in eye imaging. Use of an asymmetric illumination method to compensate for the imbalance illumination caused by the nose reflection is described. In one embodiment, a method for balancing infrared illumination in eye imaging comprises generating one or more eye images, using the images to detect the imbalance illuminations from the nasal sclera and temporal sclera with the selected region of interest (“ROI”). In another embodiment, a system for balancing illuminations in eye imaging uses the detected imbalance illumination ratio of nasal/temporal sclera as the signal for adjusting the brightness of the infrared LEDs for asymmetric illumination. 
     Other systems, methods, features and advantages of the invention will be or will become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional systems, methods, features and advantages be included within this description, be within the scope of the invention, and be protected by the accompanying claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       To better appreciate how the above-recited and other advantages and objects of the inventions are obtained, a more particular description of the embodiments briefly described above will be rendered by reference to specific embodiments thereof, which are illustrated in the accompanying drawings. It should be noted that the components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. Moreover, in the figures, like reference numerals designate corresponding parts throughout the different views. However, like parts do not always have like reference numerals. Moreover, all illustrations are intended to convey concepts, where relative sizes, shapes and other detailed attributes may be illustrated schematically rather than depicted literally or precisely. 
         FIG. 1  shows exemplary eye images. 
         FIG. 2   a  schematically illustrates simplified measurement systems according to a preferred embodiment of the present invention. 
         FIG. 2   b  is a perspective view of a laser eye surgery system according to a preferred embodiment of the present invention. 
         FIG. 3  is a simplified diagram of a computer system according to a preferred embodiment of the present invention. 
         FIG. 4   a  shows eye images according to a preferred embodiment of the present invention. 
         FIG. 4   b  shows other eye images according to a preferred embodiment of the present invention. 
         FIG. 4   c  shows eye images of a patient according to a preferred embodiment of the present invention. 
         FIG. 4   d  shows eye images of another patient according to a preferred embodiment of the present invention. 
         FIG. 4   e  shows imbalance illumination ratios of two patients according to a preferred embodiment of the present invention. 
         FIG. 5  is a flowchart illustrating a process according to a preferred embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention is generally directed to systems and methods for balancing infrared illuminations in eye imaging. An embodiment of the invention generally balances the infrared illuminations in eye imaging by extracting the nasal and temporal imbalance illumination ratio in the eye images, and using the imbalance ratio to adjust the infrared LED&#39;s brightness for nasal and temporal illumination, thereby compensating for the imbalance. 
     The balancing of infrared illumination as described in the preferred embodiments of the invention may be used in stand-alone ophthalmic diagnostic and measurement systems, in a laser eye surgery system having an integrated ophthalmic diagnostic and measurement system, in an eye tracking system of an ophthalmic surgical system, and the like. 
     Turning to  FIG. 2   a , illustrations of a first measurement system  10  and a second measurement system  16  are shown. In an embodiment, the first measurement system  10  is a wavefront measurement device  10  that measures aberrations and other optical characteristics of an ocular or other optical tissue system. The data from such a wavefront measurement device may be analyzed by a computer system  17  and used to generate an optical surface from an array of optical gradients. 
     In another embodiment, the second measurement system  16  is a corneal topographer  16 . Corneal topographer  16  may be used to diagnose and examine the corneal surface. Corneal topographer  16  typically includes an imaging device  18 , such as a frame grabber that takes images of the cornea. The images obtained by the frame grabber are analyzed by a computer system  19 , and the computer system  19  may generate one or more graphical and/or tabular outputs, including three dimensional topographical maps. 
     Turning to  FIG. 2   b , illustration of a laser surgery system  15  is shown. In an embodiment, the laser surgery system  15  includes a laser assembly  12  that produces a laser beam  14 . Laser assembly  12  is optically coupled to laser delivery optics  16 , which directs laser beam  14  to an eye E of a patient. An imaging assembly  20 , including a microscope, is mounted on a delivery optics support structure (not shown here, but for clarity, see incorporated U.S. Pat. No. 7,931,371 and other herein incorporated patents for further detail) to image the cornea of eye E during the laser procedure. Laser assembly  12  generally comprises an excimer laser source, typically comprising an argon-fluorine laser producing pulses of laser light having a wavelength of approximately 193 nm. Laser assembly  12  may be designed to provide a feedback stabilized fluence at the patient&#39;s eye E, delivered via delivery optics  16 . Although an excimer laser is the illustrative source of an ablating beam, other lasers may be used. 
     Laser assembly  12  and delivery optics  16  generally direct laser beam  14  to the eye E under the direction of a computer system  22 . Computer system  22  may selectively adjust laser beam  14  to expose portions of the cornea to the pulses of laser energy so as to effect a predetermined sculpting of the cornea and alter the refractive characteristics of the eye. In many embodiments, both laser beam  14  and the laser delivery optical system will be under computer control of computer system  22  to affect the desired laser sculpting process so as to deliver a customized ablation profile, with the computer system  22  ideally altering the ablation procedure in response to inputs from an optical feedback system (not shown here, but for clarity, see incorporated U.S. Pat. No. 7,931,371 and other herein incorporated patents for further detail). The feedback may be input into computer system  22  from an automated image analysis system  21 , or may be manually input into the processor by a system operator using a user input interface device  62  ( FIG. 3 ) in response to a visual inspection of analysis images provided by the optical feedback system. Computer system  22  often continues and/or terminates a sculpting treatment in response to the feedback, and may optionally also modify the planned sculpting based at least in part on the feedback. 
     Computer system  17 ,  19 ,  22  may comprise (or interface with) a conventional or special computer, such as a personal computer (PC), laptop, and so on, including the standard user interface devices such as a keyboard, a mouse, a touch pad, foot pedals, a joystick, a touch screen, an audio input, a display monitor, and the like. Computer system  17 ,  19 ,  22  typically includes an input device such as a magnetic or optical disk drive, or an input interface such as a USB connection, a wired and/or wireless network connection, or the like. Such input devices or interfaces are often used to download a computer executable code, to a storage media  29 , embodying any of the methods of the present invention. Storage media  29  may take the form of an optical disk, a data tape, a volatile or non-volatile memory, RAM, or the like, and the computer system  17 ,  19 ,  22  includes the memory and other standard components of modern computer systems for storing and executing this code. Storage media  29  may alternatively be remotely operatively coupled with computer system  22  via network connections such as LAN, the Internet, or via wireless methods such as WLAN, Bluetooth, or the like. 
     Additional components and subsystems may be included with laser system  15 , as should be understood by those of skill in the art. For example, spatial and/or temporal integrators may be included to control the distribution of energy within the laser beam, as described in U.S. Pat. No. 5,646,791, the full disclosure of which is incorporated herein by reference. Ablation effluent evacuators/filters, aspirators, and other ancillary components of the laser surgery system are known in the art. Further details of suitable systems for performing a laser ablation procedure can be found in commonly assigned U.S. Pat. Nos. 4,665,913, 4,669,466, 4,732,148, 4,770,172, 4,773,414, 5,207,668, 5,108,388, 5,219,343, 5,646,791 and 5,163,934, the complete disclosures of which are incorporated herein by reference. 
       FIG. 3  is a simplified block diagram of an exemplary computer system  17 ,  19 ,  22  that may be used in measurement instrument  10 , measurement instrument  16 , and laser surgical system  15 . Computer system  17 ,  19 ,  22  typically includes at least one processor  52  which may communicate with a number of peripheral devices via a bus subsystem  54 . These peripheral devices may include a storage subsystem  56 , comprising a memory subsystem  58  and a file storage subsystem  60  (which may include storage media  29 ), user interface input devices  62 , user interface output devices  64 , and a network interface subsystem  66 . Network interface subsystem  66  provides an interface to outside networks  68  and/or other devices. 
     User interface input devices  62  may include a keyboard, pointing devices such as a mouse, trackball, touch pad, or graphics tablet, a scanner, foot pedals, a joystick, a touch screen incorporated into the display, audio input devices such as voice recognition systems, microphones, and other types of input devices. User interface input devices  62  are often used to download a computer executable code from a storage media  29  embodying any of the methods of the present invention. User interface input devices  62  are also used to control an eye fixation system. In general, use of the term “input device” is intended to include a variety of conventional and proprietary devices and ways to input information into computer system  17 ,  19 ,  22 . 
     User interface output devices  64  may include a display subsystem, a printer, a fax machine, or non-visual displays such as audio output devices. The display subsystem may be a cathode ray tube (CRT), a flat-panel device such as a liquid crystal display (LCD), a projection device, or the like. The display subsystem may also provide a non-visual display such as via audio output devices. In general, use of the term “output device” is intended to include a variety of conventional and proprietary devices and ways to output information from computer system  17 ,  19 ,  22  to a system operator. 
     Storage subsystem  56  can store the basic programming and data constructs that provide the functionality of the various embodiments of the present invention. For example, a database and modules implementing the functionality of the methods of the present invention, as described herein, may be stored in storage subsystem  56 . These software modules are generally executed by processor  52 . In a distributed environment, the software modules may be stored on a plurality of computer systems and executed by processors of the plurality of computer systems. Storage subsystem  56  typically comprises memory subsystem  58  and file storage subsystem  60 . 
     Memory subsystem  58  typically includes a number of memories including a main random access memory (RAM)  70  for storage of instructions and data during program execution and a read only memory (ROM)  72  in which fixed instructions are stored. File storage subsystem  60  provides persistent (non-volatile) storage for program and data files, and may include storage media  29  ( FIG. 2   b ). File storage subsystem  60  may include a hard disk drive along with associated removable media, a Compact Disk (CD) drive, an optical drive, DVD, solid-state removable memory, and/or other removable media cartridges or disks. One or more of the drives may be located at remote locations on other connected computers at other sites coupled to computer system  22 . The modules implementing the functionality of the present invention may be stored by file storage subsystem  60 . 
     Bus subsystem  54  provides a mechanism for letting the various components and subsystems of computer system  17 ,  19 ,  22  communicate with each other as intended. The various subsystems and components of computer system  17 ,  19 ,  22  need not be at the same physical location but may be distributed at various locations within a distributed network. Although bus subsystem  54  is shown schematically as a single bus, alternate embodiments of the bus subsystem may use multiple busses. 
     Computer system  17 ,  19 ,  22  itself can be of varying types including a personal computer, a portable computer, a workstation, a computer terminal, a network computer, a control system in a wavefront measurement system or laser surgical system, a mainframe, or any other data processing system. Due to the ever-changing nature of computers and networks, the description of computer system  17 ,  19 ,  22  depicted in  FIG. 3  is intended only as an example for purposes of illustrating one embodiment of the present invention. Many other configurations of computer system  22 , having more or fewer components than the computer system depicted in  FIG. 3 , are possible. 
     Turning to  FIG. 4   a , an exemplary technique for detection of imbalance illumination  400  is illustrated. Eye images captured by the pupil camera of measurement system  10 ,  16  or laser surgery system  15  are analyzed to estimate the imbalance illumination level at the sclera on the nasal and the temporal sides.  FIG. 4   a  shows the raw eye image  410  in image (a) and the detected outer iris boundary (OIB)  410 ,  411  in image (b) using image processing of the image analysis system  21 . From the detected OIB  410 ,  411  information, two regions of interest (ROI)  420 ,  421  may be selected on the sclera in the eye image, including one on the nasal side  420  and one on the temporal side  421 , shown in image (c). The ROIs may be automatically selected, or manually selected by a system operator. The ROIs  420 ,  421  are typically located just outside of the OIB. Parameter a  422  and b  423  may then be generated automatically or by the system operator. Parameter a represents the desired height of ROIs  420 ,  421 . Parameter b  423  represents the desired width of ROIs  420 ,  421 . Image (d) shows an exemplary extracted eye image of ROIs  430 ,  431 , after applying parameters a and b, and which will be used to calculate the imbalance illumination ratio of the nasal and temporal sides on the sclera. The dot  440  in image (d) is the center of OIB. 
     Turning to  FIG. 4   b , to avoid the patient&#39;s eyelid getting into the selected ROI, parameter a  422  and parameter b  423  may be used to change the size and location of ROIs  420 ,  421 , as shown in ROIs  420 ′,  421 ′, and  420 ″,  421 .″ 
     After the desired ROIs have been selected, average intensity of the ROIs can be calculated as following, 
     
       
         
           
             
               I 
               nasal 
             
             = 
             
               mean 
               ⁡ 
               
                 ( 
                 
                   I 
                   
                     ROI 
                     n 
                   
                 
                 ) 
               
             
           
         
       
       
         
           
             
               I 
               temporal 
             
             = 
             
               mean 
               ⁡ 
               
                 ( 
                 
                   I 
                   
                     ROI 
                     t 
                   
                 
                 ) 
               
             
           
         
       
     
     I nasal  is the average intensity of the ROIs on the nasal side, while I temporal  is the average intensity of the ROIs on the temporal side. 
     Then the imbalance illumination ratio of the nasal and temporal sides of the sclera can be calculated as following, 
     
       
         
           
             Ratio 
             = 
             
               
                  
                 
                   
                     I 
                     nasal 
                   
                   - 
                   
                     I 
                     temporal 
                   
                 
                  
               
               
                 mean 
                 ⁡ 
                 
                   ( 
                   
                     
                       I 
                       nasal 
                     
                     , 
                     
                       I 
                       temporal 
                     
                   
                   ) 
                 
               
             
           
         
       
     
     This imbalance ratio can be used to adjust, (either automatically or manually by the system operator), the infrared LED&#39;s brightness for nasal and temporal illumination to compensate for the imbalance illumination caused by nasal reflection in the eye image. The adjustment and compensation may be repeated until the imbalance ratio reaches a predetermined or desired tolerance level, e.g., 10%. 
     Turning to  FIGS. 4   c - 4   e , in another embodiment, the exemplary imbalance illumination ratios of two patients are shown.  FIG. 4   c  shows eye images captured by one diagnostic system from patient 1  and patient 2  with selected ROIs.  FIG. 4   d  shows eye images captured by another diagnostic system from patient 3  and patient 4  with selected ROIs.  FIG. 4   d  shows a table of imbalance ratio detected from the four eyes. 
     Turning to  FIG. 5 , a process  500  for imbalance illumination detection and compensation according to an embodiment of the invention is shown. The process starts with a first set of (raw) eye images taken by the diagnostic and measurement system (Action Block  510 ). The OIB is detected from the eye images using image processing (Action Block  520 ). From the detected OIB information, parameters a and b are generated and ROIs are selected with the generated parameters a and b (Action Block  530 ). The ROIs from the nasal and temporal sclera are analyzed using their average intensities, which are in turn used to calculate the imbalance ratio (Action Block  540 ). If the imbalance ratio does not reach a predetermined or desired tolerance level (Decision Block  550 ), e.g., &lt;10%, then the brightness of the LEDs may be adjusted (Action Block  560 ) until the desired tolerance level is reached. 
     In the foregoing specification, the invention has been described with reference to specific embodiments thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention. For example, the reader is to understand that the specific ordering and combination of process actions described herein are merely illustrative and that the invention may appropriately be performed using different or additional process actions or a different combination or ordering of process actions. For example, while this invention is particularly suited for wavefront acquisition and diagnostic system, and/or laser-based ophthalmic surgical systems, it can be used for any acquisition and diagnostic system and/or ophthalmic surgical system. 
     Additionally and obviously, features may be added or subtracted as desired. Accordingly, the invention is not to be restricted except in light of the attached claims and their equivalents.