Spectral domain optical coherence tomography system

Abstract

An ophthalmic imaging device for improved ophthalmic imaging including: an optical coherence scanning device, a fundus imaging device: an iris viewer; a motorized chin rest; an internal test target, and a fixation target device wherein the optical coherence scanning device, the ophthalmic scanning device, the iris viewer, and the fixation target device all share at least one common optical element. The optical coherence device preferably employs a Mach-Zehnder interferometer with an all fiber reference path; monitoring and attenuating power within the reference path. The multiple devices are separately and in combination aligned with the eye. The system includes internal and external calibration and improved image formats.

1 . An ophthalmic imaging device comprising: 
 an optical coherence tomography (OCT) system including a first light source for generating a first radiation beam;    a fundus imaging system including a second light source generating a second radiation beam;    optics for combining the first and second radiation beams and directing the combined beams into the eye of a patient in a manner such that the OCT system and the fundus imaging system are confocal; and    an iris viewing system including an imaging device and optics for obtaining an image of the iris along an axis common with the combined first and second radiation beams whereby the OCT system and the fundus imaging system can be aligned with the patient's eye based on images generated by the iris viewing system and wherein the images generated by the OCT system and the fundus imaging system are aligned.    
     
     
         2 . An imaging device as recited in  claim 1 , further including a fixation system for generating an image of a target and including optics for projecting the image of the target into the eye along axis common with the combined first and second radiation beams to aid the patient in rotating the eye relative to the OCT and fundus imaging systems.  
     
     
         3 . The imaging device as recited in  claim 1 , wherein the OCT system is a frequency domain optical coherence tomography scanner.  
     
     
         4 . The imaging device as recited in  claim 1 , wherein the fundus imaging system is a line scanning ophthalmoscope.  
     
     
         5 . The imaging device as recited in  claim 1 , wherein the OCT system contains a Mach-Zehnder interferometer.  
     
     
         6 . The imaging device as recited in  claim 1 , wherein the OCT system contains an optical coupler in which one tap is used to monitor optical power.  
     
     
         7 . The imaging device as recited in  claim 1 , for imaging an eye further comprising: 
 the OCT system having a component conjugate to an image plane in a first region of the eye; and    the a fundus imaging system having a component conjugate to an image plane in a second region of the eye; wherein    the first and second regions of the eye are at different depths.    
     
     
         8 . An ophthalmic imaging device comprising: 
 an optical coherence scanning device;    a fundus imaging device;    an iris viewer;    a motorized chin rest; and    a fixation target device wherein the optical coherence scanning device, the ophthalmic scanning device, the iris viewer, and the fixation target device all share at least one common optical element.    
     
     
         9 . The ophthalmic imaging device as recited in  claim 8 , wherein at least one common optical element is a lens.  
     
     
         10 . The ophthalmic imaging device as recited in  claim 8 , further comprising an ocular lens, said ocular lens being the optical element closest to the patient, wherein 
 the motorized chin rest positions the patient with respect to the imaging device; and    the ocular lens is arranged to be disposed to be adjusted in position wherein the position of the ocular lens is separately adjustable relative to the chin rest and jointly adjustable with the chin rest relative to the remainder of the optical elements of the imaging device.    
     
     
         11 . A method for ophthalmic imaging comprising: 
 moving the subject to align focus of a first optical device;    aligning a plurality of optical devices while retaining focus alignment of the first optical device;    creating an image of the interior of an eye with an optical coherence scanning device;    creating a fundus image of the posterior of the eye;    creating an image of the iris of the eye; and    projecting a fixation target to be viewed by the eye wherein the optical coherence scanning device, the ophthalmic scanning device, the iris viewer, and the fixation target device are all optical devices and all operate essentially simultaneously.    
     
     
         12 . The method of  claim 11 , wherein the first optical device is an iris viewer.  
     
     
         13 . The method of  claim 11 , wherein the optical coherence scanning device is a spectral domain Optical Coherence Tomography scanner.  
     
     
         14 . The method of  claim 11 , wherein the fundus imaging device is a line scanning ophthalmoscope.  
     
     
         15 . The method of  claim 11 , wherein least one common optical element is a lens.  
     
     
         16 . The method of  claim 11 , wherein the interior portion of the eye scanned by the optical coherence scanning device is the retina.  
     
     
         17 . The method of  claim 11 , wherein the interior portion of the eye scanned by the optical coherence scanning device is the cornea.  
     
     
         18 . The method of  claim 17 , wherein the optical coherence scanning device is switched from scanning the retina to scanning the cornea by inserting a lens in the OCT beam path.  
     
     
         19 . The method of  claim 11 , wherein the subject is moved using a motorized chinrest to center the image of the iris.  
     
     
         20 . The method of  claim 18 , wherein the ophthalmic alignment focuses the fundus image by moving the subject and an optical component of the ophthalmic device concurrently.  
     
     
         21 . The method of  claim 20 , wherein the optical component of the ophthalmic device is an ocular lens.  
     
     
         22 . The method of  claim 21 , wherein the OCT image of the eye is created by: 
 setting an OCT depth range;    adjusting an OCT polarization compensation;    selecting an OCT scan pattern;    adjusting an OCT transverse scanning region; and    acquiring an OCT image of the eye.    
     
     
         23 . The method of  claim 22 , further comprising the step of setting the patient's prescription.  
     
     
         24 . The method of  claim 22 , further comprising the step of adjusting a lens within the ophthalmic scanning device to optimize image brightness.  
     
     
         25 . An ophthalmic imaging device comprising: 
 an optical coherence scanning device;    a fundus imaging device;    an iris viewer;    an internal test target; and    a fixation target device wherein during an optical examination, the optical coherence scanning device, the ophthalmic scanning device, the iris viewer, and the fixation target device all share at least one common optical element.    
     
     
         26 . The method of  claim 25 , wherein the internal test target comprises a series of horizontal and vertical strips.  
     
     
         27 . An optical coherence tomography scanner comprising a longitudinal delay device, an interferometer, a corner cube, and a transverse scanner, wherein the longitudinal delay device lies between the interferometer and the transverse scanner.  
     
     
         28 . An optical coherence tomography scanner as recited in  claim 27 , wherein the optical coherence source beam is in free space between the longitudinal delay and the transverse scanner.  
     
     
         29 . An optical coherence tomography scanner as recited in  claim 28 , wherein the longitudinal delay device includes the corner cube.  
     
     
         30 . An optical coherence tomography scanner as recited in  claim 29 , wherein the corner cube is mounted on a rail and the rail is mounted on a plate where the plate design reduces thermal variation misalignment of the corner cube as the corner cube traverses the rail.  
     
     
         31 . An optical coherence tomography scanner as recited in  claim 29 , wherein at least one surface of the corner cube is coated to reduce reflections.  
     
     
         32 . An optical coherence tomography scanner as recited in  claim 27 , wherein the optical coherence scanning device further includes a scanner adjustment device for the purpose of adjusting the center of the beam on a central axis of the scanner.  
     
     
         33 . An optical coherence tomography scanner as recited in  claim 32 , wherein the adjustment device includes a mirror.  
     
     
         34 . An optical coherence tomography scanner as recited in  claim 32 , wherein the adjustment device adjust the optical coherence beam to maintain a position error below 10 microns at the entrance to the scanner while the longitudinal delay is varied by more than 30 mm.  
     
     
         35 . An optical coherence tomography scanner as recited in  claim 32 , wherein the adjustment reduces the phase shift associated with scanning.  
     
     
         36 . An optical coherence tomography scanner as recited in  claim 35 , wherein the adjustment device maintains a phase shift below the phase shift corresponding to 1 mm/s axial motion of the sample, while the scanner scans the OCT beam over more than 2 mm on the subject and while the longitudinal delay is varied by more than 30 mm.  
     
     
         37 . An optical coherence tomography scanner as recited in  claim 27 , wherein the optical coherence scanning device further includes an alignment mechanism capable of aligning the beam parallel to the axis of the longitudinal delay.  
     
     
         38 . An optical coherence tomography scanner as recited in  claim 37 , wherein the alignment mechanism reduces the transverse motion of the optical coherence beam at the scanner associated with changes in longitudinal delay.  
     
     
         39 . An optical coherence tomography scanner comprising a reference path in fiber and a reference power device within the reference path for setting the reference power.  
     
     
         40 . An optical coherence tomography scanner as recited in  claim 39 , wherein the reference power device is a fiber tap and the reference power is set by the coupling ratio in the fiber tap.  
     
     
         41 . An optical coherence tomography scanner as recited in  claim 40 , wherein the fiber tap removes power from the reference path, and some of the removed power is received by an optical detector.  
     
     
         42 . An optical coherence tomography scanner as recited in  claim 39 , wherein the reference power device is a length of fiber with optical loss.  
     
     
         43 . An optical coherence tomography scanner as recited in  claim 39 , wherein the optical coherence tomography scanner is a frequency domain optical coherence tomography scanner.  
     
     
         44 . An optical coherence tomography scanner as recited in  claim 39 , wherein the reference power device includes a fiber-based device through which optical transmission depends on polarization state of the light, and further includes a fiber-based polarization controller.  
     
     
         45 . An optical coherence tomography scanner comprising a reference path in fiber and a sample path and operating at a wavelength having significant chromatic dispersion mismatch between the reference path and the sample path.  
     
     
         46 . An optical coherence tomography scanner as recited in  claim 45 , wherein the sample path includes materials of high chromatic dispersion.  
     
     
         47 . An optical coherence tomography scanner as recited in  claim 45 , where the reference and sample paths include loops of substantially equal path length, and in which the loops are individually compensated to have insignificant polarization mode dispersion.  
     
     
         48 . An optical coherence tomography scanner as recited in  claim 45 , where the reference path fiber is routed with bends in different planes, the radii of these bends being chosen to substantially cancel the bending-induced polarization mode dispersion.  
     
     
         49 . An optical coherence tomography scanner as recited in  claim 45 , including at least one path in optical fiber along which the optical fiber is routed with bends in different planes, the radii of these bends being chosen to substantially cancel the bending-induced polarization mode dispersion.  
     
     
         50 . An ophthalmic imaging device comprising: 
 a first imaging system having a component conjugate to an image plane in a first region of the eye;    a second imaging system having a component conjugate to an image plane in a second region of the eye;    wherein first and second regions of the eye are at different depths; and    wherein first and second imaging systems share a common portion of an optical path.    
     
     
         51 . A device as recited in  claim 50 , wherein the first imaging system is a retinal imager and the associated image plane corresponds to a layer posterior to the RPE and the second imaging system is a scanning retinal imager and the associated image plane is located anterior to the image plane of the first imaging system.  
     
     
         52 . A method of generating images of a eye using an optical coherence tomography (OCT) system, said system including a light source for generating a radiation beam and a scanning mechanism for moving the beam to a plurality of positions within an X/Y plane and wherein the OCT system obtains a measurement of a reflectance distribution within the eye as a function of depth (Z) at each X and Y position, said method comprising the steps of: 
 obtaining a first set of depth scans a spaced positions along an X axis at a first Y position;    obtaining a second set of depth scans at spaced positions along an X axis at a second Y position near the first Y position and wherein the X positions of the second set of depth scans are offset from the X positions in the first set of depth scans; and    generating a two dimensional slice image along the X axis as a function of depth by treating the measurements as if they were obtained along a common Y position.    
     
     
         53 . A method of generating images of a eye using an optical coherence tomography (OCT) system, said system including a light source for generating a radiation beam and a scanning mechanism for moving the beam to a plurality of positions within an X/Y plane and wherein the OCT system obtains a measurement of a reflectance distribution within the eye as a function of depth (Z) at each X and Y position, said method comprising the steps of: 
 scanning the beam generally along the X direction at a particular Y axis position, said Y axis position defining a centerline of the scan, and while scanning the beam, varying the position of the beam on the Y axis about the centerline while obtaining depth scans at spaced X positions; and    generating a two dimensional slice image along the X axis as a function of depth by treating the measurements as if they were obtained along a common Y position.    
     
     
         54 . A method of generating images of a eye using an optical coherence tomography (OCT) system, said system including a light source for generating a radiation beam and a scanning mechanism for moving the beam to a plurality of positions within an X/Y plane and wherein the OCT system obtains a measurement of a reflectance distribution within the eye as a function of depth (Z) at each X and Y position, said method comprising the steps of: 
 scanning the beam generally along the line and while scanning the beam, dithering the lateral position of the beam with respect to the line while obtaining depth scans at a plurality of positions; and    generating a two dimensional slice image along the line as a function of depth by treating all the measurements as if they were obtained along said line.    
     
     
         55 . A device as recited in  claim 54 , wherein the line is curved.  
     
     
         56 . A method of obtaining B-scan data with reduced speckle in optical coherence tomography (OCT) comprising: 
 acquiring a plurality of OCT A-scans; and    forming a B-scan from said A-scans, wherein the A-scans within one resolution cell of the B-scan contains a subset of A-scans which are speckle diverse both tangent to and orthogonal to the B-scan at that cell.    
     
     
         57 . A device as recited in  claim 56 , wherein the B-scan is substantially planar.  
     
     
         58 . A device as recited in  claim 56 , wherein the B-scan is substantially cylindrical.  
     
     
         59 . A device as recited in  claim 56 , wherein the subset of A-scans are compounded to represent the resolution cell of the B-scan.  
     
     
         60 . A device as recited in  claim 59 , wherein the subset of A-scans are sequentially acquired.  
     
     
         61 . A method for improving the long term performance of an ophthalmic scanning device in which a galvanometer is positioned by a motor comprising: 
 generating a command to direct the motor driving the galvanometer to a desired position;    characterizing the closed-loop response of the galvanometer to the generating command; and    adjusting one of the command or the closed loop response to achieve a desired galvanometer position.    
     
     
         62 . A method as recited in  claim 61 , wherein the adjusting step modifies the position command.  
     
     
         63 . A method as recited in  claim 61 , wherein the closed-loop response of the galvanometer includes a loop filter controlling a servo and the adjusting step adapts the loop filter to keep the closed-loop response constant.