Classifications

• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61F—FILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
  • A61F9/00—Methods or devices for treatment of the eyes; Devices for putting in contact-lenses; Devices to correct squinting; Apparatus to guide the blind; Protective devices for the eyes, carried on the body or in the hand
  • A61F9/007—Methods or devices for eye surgery
  • A61F9/008—Methods or devices for eye surgery using laser
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B18/00—Surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body
  • A61B18/18—Surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body by applying electromagnetic radiation, e.g. microwaves
  • A61B18/20—Surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body by applying electromagnetic radiation, e.g. microwaves using laser
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61F—FILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
  • A61F9/00—Methods or devices for treatment of the eyes; Devices for putting in contact-lenses; Devices to correct squinting; Apparatus to guide the blind; Protective devices for the eyes, carried on the body or in the hand
  • A61F9/007—Methods or devices for eye surgery
  • A61F9/008—Methods or devices for eye surgery using laser
  • A61F9/00802—Methods or devices for eye surgery using laser for photoablation
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
  • B23K26/02—Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
  • B23K26/03—Observing, e.g. monitoring, the workpiece
  • B23K26/032—Observing, e.g. monitoring, the workpiece using optical means
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
  • B23K26/02—Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
  • B23K26/06—Shaping the laser beam, e.g. by masks or multi-focusing
  • B23K26/062—Shaping the laser beam, e.g. by masks or multi-focusing by direct control of the laser beam
  • B23K26/0622—Shaping the laser beam, e.g. by masks or multi-focusing by direct control of the laser beam by shaping pulses
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
  • B23K26/70—Auxiliary operations or equipment
  • B23K26/702—Auxiliary equipment
  • B23K26/705—Beam measuring device
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
  • G01J1/00—Photometry, e.g. photographic exposure meter
  • G01J1/42—Photometry, e.g. photographic exposure meter using electric radiation detectors
  • G01J1/4257—Photometry, e.g. photographic exposure meter using electric radiation detectors applied to monitoring the characteristics of a beam, e.g. laser beam, headlamp beam
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61F—FILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
  • A61F9/00—Methods or devices for treatment of the eyes; Devices for putting in contact-lenses; Devices to correct squinting; Apparatus to guide the blind; Protective devices for the eyes, carried on the body or in the hand
  • A61F9/007—Methods or devices for eye surgery
  • A61F9/008—Methods or devices for eye surgery using laser
  • A61F2009/00855—Calibration of the laser system
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61F—FILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
  • A61F9/00—Methods or devices for treatment of the eyes; Devices for putting in contact-lenses; Devices to correct squinting; Apparatus to guide the blind; Protective devices for the eyes, carried on the body or in the hand
  • A61F9/007—Methods or devices for eye surgery
  • A61F9/008—Methods or devices for eye surgery using laser
  • A61F2009/00861—Methods or devices for eye surgery using laser adapted for treatment at a particular location
  • A61F2009/00872—Cornea

Definitions

• the present invention relates generally to methods and systems for calibrating laser beam delivery systems, particularly ophthalmological surgery systems. More specifically, the present invention relates to methods and systems for calibrating a laser beam, such as a position or shape of the laser beam, from the laser beam delivery system using an image capture device.
• Laser based systems are now commonly used in ophthalmological surgery on corneal tissues of the eye to correct vision defects. These systems use lasers to achieve a desired change in corneal shape, with the laser removing microscopic layers of stromal tissue from the cornea using a technique generally described as ablative photodecomposition to alter the refractive characteristics of the eye.
• Laser eye surgery techniques are useful in procedures such as photorefractive keratotomy (PRK), phototherapeutic keratectomy (PTK), laser in situ keratomileusis (LASIK), and the like.
• Laser ablation procedures can reshape or sculpt the shape of the cornea for varying purposes, such as for conecting myopia, hyperopia, astigmatism, and other corneal surface profile defects.
• the laser beam often comprises a series of discrete pulses of laser light energy, with the total shape and amount of tissue being removed being determined by the position, shape, size, and/or number of a pattern of laser energy pulses impinging on the cornea.
• a variety of algorithms may be used to calculate the pattern of laser pulses used to reshape the cornea so as to conect a refractive error of the eye.
• derivation from a desired laser beam shape, size, or position may result in tissue ablation at an undesired location on the patient's cornea which in turn leads to less than ideal corneal sculpting results.
• a desired laser beam shape, size, or position such as the laser beam exhibiting a non-symmetrical shape or an increased or decreased laser beam diameter
• Ablation of plastic test materials are often perforated prior to laser surgery to calibrate the ablation shape and size of the laser beam delivery system.
• an iris or other variable diameter aperture which may be used to tailor the shape, size, and position of the laser beam is typically calibrated by directing laser pulses at different iris settings onto a clear plastic material. Eye loops are then used by an operator for manual inspection of the ablated plastic.
• Such calibration techniques are limited by many factors, such as the precision provided by the eye loops, which is typically about ⁇ 0.1 mm, and/or the vision of the operator. For example, visual measurement of shape profiles is particularly difficult and is often subject to human error. Further, such calibration techniques may not accurately measure a hysteresis of the variable diameter iris.
• increased utilization of wavefront tec-hnologies to provide customized ablations in laser eye surgery systems may be optimized by increasing the accuracy of the shape, size, and positioning of the ablating laser beam.
• the present invention provides methods and systems for calibrating a laser beam delivery system, such as an excimer laser system for selectively ablating a cornea of a patient's eye.
• a laser beam delivery system such as an excimer laser system for selectively ablating a cornea of a patient's eye.
• improved methods and systems are provided for laser beam 0 positioning, shape profile, and/or size profile calibration using an image capture device, such as a microscope camera.
• the methods and systems are particularity suited for iris calibration and hysteresis measurement of a variable diameter aperture.
• Such, methods and systems further provide enhanced calibration accuracy and precision withoiit significantly increasing the overall system cost and complexity and may be applied to a va ⁇ riety of laser systems.
• a method for calibrating laser pulses from a laser eye surgery system using an image capture device comprises imaging an object of known size placed on a calibration surface with an image capture device. A pulsed laser beam is directed onto the calibration surface so as to leave a mark on the calibration surface, wherein the known object is removed prior to directing the pulsed laser beam onto the
• the mark on the calibration surface is then imaged with the image capture device.
• the laser eye surgery system is calibrated by comparing the image of the mark on the calibration surface to the image of the known object.
• the directing and imaging may be carried out in at least one of a laser focus plane or an eye treatment plane, wherein imaging of the known object and imaging of the mark on the calibration surface are performed along an imaging optical path coaxial with a laser optical path.
• the laser energy may be
• the imaged object comprises a circular shape having a known diameter.
• the known object may comprise a circular chrome layer on a glass or crystal plate.
• the calibration surface may comprise a variety of materials, including photosensitive material, silkscreen material, Zapit paper, luminescent material, or photographic material.
• a photosensitive material is utilized, whe-rein the mark on the calibration surface comprises a penxianent change in color, such as a white spot on a black background or vice versa, or a luminescent glow.
• the calibration surface may comprise photoreactive material, polymethylmethacrylate material, or other NISX calibration materials, available from NISX, Incorporated of Santa Clara, California.
• use of polymethylmethacrylate material may result in the mark on the calibration surface to comprise an ablation.
• the mark on the calibration surface may be associated with an iris diameter setting in a range from about 0.65 mm to about 6.7 mm.
• the pulsed laser beam diameter setting is increased over time so as to fonn a plurality of marks.
• the resulting marks are then imaged and compared to the known object.
• the pulsed laser beam diameter setting is decreased over time so as to form another set of marks that are imaged and compared to the known object.
• a hysteresis determination may then be determined of a variable aperture, due to changes in iris diameter setting movement directions, as well as a relationship between laser beam diameter and motor counts associated with the iris setting.
• the shape of the laser beam and a center position of the laser " beam may be determined from the imaging comparison. Additionally, a drift of the laser eye surgery system may be determined by monitoring a variance in center positions for each scanned and imaged laser pulse. Still further, a laser beam deflection may be determined.
• an optical element may be rotated along a laser delivery path for smoothing laser beam integration, as discussed in greater detail in co-pending U.S. Patent Application No. 10/366,131, filed February 12, 2003, assigned to the assignee of the present application and incorporated herein by reference.
• the present calibration method may also identify a rotation-induced laser induced wobble from a plurality of marks due to rotation of the optical element.
• a patient's cornea may be ablated to correct a variety of vision defects, including myopia, hyperopia, astigmatism, and other corneal surface profile defects.
• a method for calibrating laser pulses from a laser eye surgery system using a microscope camera generally comprises imaging an object of known size with a microscope camera.
• a pulsed laser beam is scanned across a photosensitive material so as leave an ablation on the photosensitive material.
• the ablation on the photosensitive material is imaged with the microscope camera.
• An iris calibration of a laser eye surgery system is t-tien detennined by comparing the image of the ablation on the photosensitive material to the image of the known object.
• a patient's cornea may be ablated with the calibrated system.
• a system for calibrating laser pulses from a laser beam delivery system comprises an image capture device orientated toward a treatment plane.
• a known object is positionable for imaging by the image capture device.
• a pulsed laser beam delivery system is also provided.
• a calibration surface is supportable in an optical path of the pulsed laser beam so as to result in a mark on the calibration surface and for imaging of the mark on the calibration surface by the image capture device.
• a processor is coupled to the image capture device. The processor determines a calibration of the laser beam delivery system by comparing "the image of the mark on the calibration surface to the image of the known object.
• the laser beam delivery system preferably comprises a laser eye surgery system.
• the image capture device preferably comprises a microscope camera.
• video cameras, eye tracking cameras, or other existing image capture devices and cameras already provided on the laser system may be utilized.
• the known object preferably comprises a circular chrome layer of known diameter on a glass plate.
• the known object and calibration surface are imaged in the same position, wherein the known object and calibration sixrface are positioned in at least one of a laser focus plane or the treatment plane.
• the calibration surface comprises photosensitive material, silkscreen material, Zapit paper, luminescent material, photoreactive material, polymethylmethacrylate material, or photographic material.
• the mark on the calibration surface comprises an ablation, a permanent change in color, o-r a luminescent glow and has an iris setting in a range from about 0.65 mm to about 6.7 mm.
• Fig. 1 illustrates a schematic of a system for calibrating laser pulses from a laser beam delivery system constructed in accordance with the principles of the present invention.
• Fig. 2 illustrates an exploded view of a known object that may be employed in the system of Fig. 1.
• Fig. 3 illustrates a schematic view of an embodiment of the laser beam delivery system illustrated in Fig. 1.
• FIGs. 4A and 4B illustrate exploded views of images of ablated material that were ablated in a laser focus plane and imaged in an eye treatment plane.
• FIGs. 5 A and 5B illustrate exploded views of images of ablated material that were ablated and imaged in a laser focus plane.
• FIGs. 6A and 6B illustrate exploded views of images of ablated material that were ablated and imaged in an eye treatment plane.
• Fig. 7 is a table summarizing image measurements from the various ablation and imaging planes.
• Figs. 8A through 8B are graphical representations illustrating the relationship between laser beam diameter and motor counts associated with an iris setting.
• Figs. 8C through 8D are graphical representations illustrating the hysteresis relationship.
• Figs. 9A and 9B are simplified flow charts illustrating a method for calibrating laser pulses employing the system of Fig. 1.
• DETAILED DESCRIPTION OF THE INVENTION [0030]
• the present invention provides methods and systems for calibrating a laser beam delivery system, such as an excimer laser system for selectively ablating a cornea of a patient's eye.
• improved methods and systems are provided for laser beam positioning, shape profile, size profile, drift, and/or deflection calibration using an image capture device, such as a microscope camera, for enhanced calibration accuracy and precision.
• the methods and systems are particularly suited for iris calibration and hysteresis measurement of a variable diameter aperture.
• a desired corneal ablation treatment can be accurately effected without the laser beam becoming incident on undesired locations of corneal tissue causing off-center ablations.
• the calibration methods and systems of the present invention may be utilized upon replacement of any laser delivery system component, e.g., internal mechanical or optical components such as the iris, major optical re-alignment of the system, or problems with enor generation.
• FIG. 1 an exemplary calibration system 10 constructed in accordance with the principles of the present invention for calibrating laser pulses from a laser eye surgery system is schematically illustrated.
• System 10 is particularly useful for calibrating and aligning a laser ablation system of the type used to ablate a region of the cornea in a surgical procedure, such as an excimer laser used in photorefractive keratotomy (PRK), phototherapeutic keratectomy (PTK), laser in situ keratomileusis (LASIK), and the like.
• the system 10 generally comprises a laser 12, a laser beam delivery system 14, a surface, such as a photochromic minor 16, a known object 30, a calibration surface 18, an image capture device 20, and a PC workstation 22.
• the above depictions are for illustrative purposes only and do not necessarily reflect the actual shape, size, or dimensions of the calibration system 10. This applies to all depictions hereinafter.
• the known object 30, as illustrated in Fig. 2 is positioned along an imaging optical path 32 via a hinged support arm or mechanism 34 that allows movement of the known object 30 and calibration surface 18 in at least one of a laser focus plane or the treatment plane.
• the known object 30 may be placed on top of a block (not shown) coupled to the arm 34. In either embodiment, the l ⁇ iown object 30 is imaged by the microscope camera 20 and then removed.
• the laser 12 typically directs an unshaped laser beam 24 through the delivery system optics 14 which in turn directs a shaped and positioned laser beam 26 towards the minor 14 having a reflecting surface that directs the laser beam 26 onto the calibration surface 18 so as to leave a mark 28 on the calibration surface 18.
• the mark 28 on the calibration surface 18, which is positioned along the imaging optical path 32 coaxial with the laser optical path 26, is then imaged by the microscope camera 20.
• a PC workstation 22 determines a calibration of the laser beam delivery system 14 by comparing the image of the mark 28 on the calibration surface 18 to the image of the l ⁇ iown object 30.
• the PC workstation 22 generally includes a processor, random access memory, tangible medium for storing instructions, a display, and/or other storage media such as hard or floppy drives.
• the laser 12 may include, but is not limited to, an excimer laser such as an argon-fluoride excimer laser producing laser energy with a wavelength of about 193 nm.
• Alternative lasers may include solid state lasers, such as frequency multiplied solid state lasers, flash-lamp and diode pumped solid state lasers, and the like.
• Exemplary solid state lasers include ultraviolet solid state lasers producing wavelengths of approximately 188-240 nm such as those disclosed in U.S. Patent Serial Nos. 5,144,630, and 5,742,626; and in Borsutzky et al., Tunable UV Radiation at Short Wavelengths (188-240nm) Generated by Sam-Frequency Mixing in Lithium Borate, Appl.
• a variety of alternative lasers might also be used, such as infrared or femtosecond lasers.
• a pulsed solid state laser emitting infrared light energy may be used as described in U.S. Patent Nos. 6,090,102 and 5,782,822, the full disclosures of which are incorporated herein by reference.
• the laser energy generally comprises a beam formed as a series of discrete laser pulses, and the pulses may be separated into a plurality of beamlets as described in U.S. Patent No. 6,331,177, the full disclosure of which is incorporated herein by reference.
• the optical delivery system 14 preferably employs the ultraviolet laser beam in corneal ablation procedures to ablate corneal tissue in a photodecomposition that does not cause thermal damage to adjacent and underlying tissue. Molecules at the radiated surface are broken into smaller volatile fragments without substantially heating the remaining substrate; the mechanism of the ablation is photochemical, i.e. the direct breaking of intermolecular bonds. The ablation removes a layer of the stroma to change its contour for various purposes, such as conecting myopia, hyperopia, and astigmatism.
• Such systems and methods are disclosed in the following U.S. patents, the disclosures of which are hereby incorporated by reference in their entireties for all purposes: U.S. Pat. No.
• the known object 30 may comprise a circular chrome layer 36 having a 10 mm diameter on a glass plate 38.
• the use of the image of the l ⁇ iown object 30 allows the magnification of the microscope camera to be quantified.
• a fitting routine then accurately and precisely estimates the cross-sectional shape, size, and center position of the laser beam by comparison. Matrices of such images may further be used to deteraiine both long and short tenn drift of the laser eye surgery system.
• the known object 30 is imaged prior to directing the pulsed laser beam 26 onto the calibration surface 18 so that the mark 28 diameters may be calculated as the calibration procedure advances, hi some instances, the image produced may be slightly out of focus if the l ⁇ iown image 30 is positioned at the laser focus plane due to the fact that the camera 20 is oriented towards the treatment plane. Further, the camera 20 response itself may also be responsible for some slight elliptical distortions of the image. Hence, the image of the known object 30 is initially fit to an elliptical algorithm to account for such camera distortion.
• the vertical and horizontal dimensions of the chrome dot 36 are obtained and all subsequent images of the mark 28 may be rescaled according to the relative dimensions of the image of the l ⁇ iown object 30 and fit to a circle algorithm so that the characteristics of the laser beam may be precisely obtained. It will be appreciated that the illumination level should be set to the conect level prior to capturing any images with the camera 20.
• a beam 102 is generated from a suitable laser source 104, such as an argon fluoride (ArF) excimer laser beam source for generating a laser beam in the far ultraviolet range with a wavelength of about 193 nm.
• the laser beam 102 is directed to a beam splitter 106. A portion of the beam 102 is reflected onto an energy detector 108, while the remaining portion is transmitted through the beam splitter 106.
• the reflective beam splitter 106 may comprise a transmitting plate of partially absorbing material to attenuate the laser beam.
• the transmitted laser beam 102 is reflected by an adjustable minor 110 that is used to align the path of the laser beam, hi alternate embodiments, a direction of the laser beam path may be controlled with adjustable prisms.
• the laser beam 102 reflects from the minor 110 onto a rotating temporal beam integrator 112 that rotates a path of the laser beam.
• Another type of temporal beam integrator may be used to rotate the beam.
• the rotated beam emerging from the temporal integrator 112 is directed to a diffractive optic apparatus including a diffractive optic 113. In a prefened embodiment, the diffractive optic 113 is rotated with the beam 102.
• the diffractive optic is designed so that rotation of the diffractive optic 113 does not substantially change the path of the laser beam, and the path of the laser beam is stable with respect to rotation of the diffractive optic.
• the beam passes through the diffractive optic 113 and positive lens 114 and emerges as a converging beam 115.
• the converging beam 115 travels to the spatial integration plane at which a variable diameter aperture 116 is disposed.
• the spatial integration plane is disposed near the focal point of the positive lens 114.
• An apertured beam 120 emerges from the variable aperture 116.
• the variable aperture 116 is desirably a variable diameter iris combined with a variable width slit (not shown) used to tailor the shape and size profile of the beam 115 to a particular ophthalmological surgery procedure.
• the apertured beam 120 is directed onto an imaging lens 122, which may be a biconvex singlet lens with a focal length of about 125 mm.
• the beam 126 emerging from the imaging lens 122 is reflected by a minor/beam splitter 130 onto the surgical plane 132.
• the apex of the cornea of the patient is typically positioned at the surgical plane 132.
• Imaging lens 122 may be moved transverse to the beam to offset the imaged beam in order to scan the imaged beam about the surgical treatment plane 132.
• a treatment energy detector 136 senses the transmitted portion of the beam energy at the minor/beam splitter 130.
• a beam splitter 138, a microscope objective lens 140, and the microscope camera 20 form part of the observation optics.
• the beam splitter is preferably coupled to the microscope camera 20 to assist in iris calibration as well as for viewing and recording of the surgical procedure.
• a heads-up display may also be inserted in the optical path 134 of the microscope objective lens 140 to provide an additional observational capability.
• Other ancillary components of the laser optical system 14 such as the movable mechanical components driven by an astigmatism motor and an astigmatism angle motor, have been omitted to avoid prolixity.
• Figs. 4A and 4B exploded views of images that were scanned in a laser focus plane and imaged in an eye treatment plane are illustrated.
• the l ⁇ iown object 30 and calibration surface 18, which are preferably imaged in the same plane, may be positioned in at least one of a laser focus plane or a treatment plane.
• the imaging of the chrome dot 36 and imaging of the mark 28 on the calibration surface 18 are performed along the imaging optical path 32 coaxial with the laser optical path 26.
• the pulsed laser beam 26 is oriented towards the laser focus plane and the camera 20 is orientated towards the treatment plane, which is a few millimeters below the laser focus plane.
• FIG. 4A illustrates a 1 mm image of a mark 40 and Fig. 4B illustrates a 5 mm image of a mark 42.
• Both images of the marks 40, 42 were created from directing the laser beam at the laser focus plane so as to create a crisp duodecahedral pattern on the calibration surface 18.
• the operator then moves the calibration surface 18 to a treatment plane via the calibration arm 34 or block (not shown) so that a sharp image of the marks 40, 42 may be obtained for calibration purposes.
• the calibration surface 18 preferably comprises silkscreen or luminescent material, wherein the marks 40, 42 comprise a permanent change in color or a luminescent glow.
• the luminescent material may comprise a piece of glass, crystal, or polymer that is optically activated, such as chromium doped, and has a relatively long luminescent lifetime. Images may be recorded after each laser pulse, wherein the luminescence of the mark will have decayed before the next laser pulse is directed onto the luminescent surface.
• Figs. 5 A and 5B illustrate exploded views of images that were scanned and imaged in the same plane, namely the laser focus plane.
• Fig. 5A illustrates a 1 mm image of a mark 40'
• Fig. 5B illustrates a 5 mm image of a mark 42'.
• Both images of the marks 40, 42 were created from directing the laser beam at the laser focus plane so as to create a crisp duodecahedral pattern on the calibration surface 18.
• the image of the marks 40', 42' however are also taken at the laser focus plane.
• the images produced 40', 42' may be slightly out of focus as the camera 20 is oriented towards the treatment plane, a few millimeters below the laser focus plane.
• Figs. 6A and 6B illustrate exploded views of images that were scanned and imaged in the eye treatment plane.
• Fig 5 A illustrates a 1 mm image of a mark 40"
• Fig. 5B illustrates a 5 mm images of a mark 42".
• this image capture positioning involves minimal operator intervention as well, it can be seen that the defocus of the laser may result in varying gray zones, poor contrast, and other variations in the images 40", 42", which are not apparent when the laser beam is scanned in the laser focus plane.
• Fig. 7 a table summarizing image measurements from the scanning and imaging positions of Figs. 4A, 4B, 5 A, and 5B as well as measurement results obtained from utilizing a Tencor Profilometer are shown.
• the first column indicates measurements made with the iris 116 set at various diameter settings from about 0.65 mm to about 6.0 mm.
• the profilometer measurements which served as the reference measurements, were taken for each iris setting as indicated in the second column.
• the third column represents image measurements that were scanned in the laser focus plane and imaged in the treatment plane, as depicted by Figs. 4A and 4B.
• the fourth column represents measurements that were scanned and imaged in the laser focus, as depicted by Figs. 5A and 5B.
• the fifth column represents any measurement variations between the third and fourth columns.
• the sixth column represents any measurement variations between the second and third columns.
• the best possible accuracy of the fit is taken to be of the order of 1 pixel, which is about 0.02 mm.
• Table 7 shows that utilizing either an up/down fit (Figs. 4A, 4B) or an up/up fit (Figs. 5A, 5B) provides a relatively accurate and precise image measurement.
• the small differences between measured images, as indicated in the fifth and sixth columns are largely smaller than or of the order of the pixel resolution.
• improved image contrast such as by choosing a higher quality silkscreen or other calibration surfaces, may further minimize any variations in measurement readings.
• Figs. 8A and 8B graphs illustrating the relationship between laser beam diameter and motor counts associated with the iris setting are depicted.
• the first ten are canied out by increasing the laser beam diameter setting of the iris 116 over time from 0.7 mm, 1.0 mm, 1.5 mm, 2.0 mm, 2.5 mm, 3 mm, 4 mm, 5 mm, 6 mm, and 6.5 mm.
• Each mark or ablation is produced by firing 100 pulses at 20 Hz with energy between 180- 220 ml from the laser 12 onto the calibration surface 18.
• a one second pause allows any smoke to dissipate prior to capturing the image of the mark 28 with the camera 20 and calculating the measured iris diameter by comparison to the known object 30.
• the next 100 pulses are then fired at the next increasing diameter without moving the calibration surface 18. This routine will continue through the 6.5 mm setting and will take about one minute.
• the second set of marks or ablations 28 will proceed in a similar manner except that a new calibration surface or a different place on the existing calibration surface will be utilized and the iris 116 will be cycled to the 6.7 mm diameter setting wherein the pulsed laser beam diameter setting is decreased over time, hi general, the scanning and imaging process is time efficient in that it generally takes less than three minutes to complete.
• any hysteresis due to changes in iris diameter setting movement directions may be determined for the iris 116 and accounted for.
• both sets of data may be used to produce interpolation curves for determining an accurate relationship between measured laser beam diameter and motor counts associated with an iris aperture.
• a drift of the laser eye surgery system 14 may be determined by monitoring a variance in center positions for each scanned and imaged laser pulse. It will be appreciated that drifts may be dependent upon several factors, such as the manner in which the laser is used between measurements, the particular set of system parameters, and/or changes in environmental conditions such as temperature. Still further, a laser beam deflection may be determined. As the iris 116 changes diameter, the center of the aperture may shift slightly. As a result of the calculations already performed, the center of the best fit to the shape of the dodecagon pattern on the calibration surface has been determined for each iris size. A plot of the x and y positions of the shape center can then be computed as a function of iris diameter.
• Best fit lines can be independently fit through the x and y positions as a function of iris diameters. Hence, when a particular diameter is required by a treatment the necessary correction for the shift of the laser beam can be calculated from these lines and the laser beam target position adjusted accordingly.
• the techniques of the present invention can also be applied to judge the stability of the laser delivery system 14.
• the calibration arm 34 supporting the calibration surface 18 may comprise a luminescent plate. After each laser pulse, an image is captured while the plate is still emitting light. Images are then analyzed as described above. The center positions are calculated and may be plotted on x and y axes so that the plot provides a map of where the laser pulses landed. This plot can then be used to deten ⁇ ine any systematic movement of the laser beam with time. Alternatively, the raw data can be used to determine parameters such as the statistical variations in x and y positions.
• a number of the optical elements in the optical system 14 may be rotated along the laser delivery path, as described in detail in co-pending U.S. Patent Application No. 10/366,131, to distribute any distortion caused by imperfections of the optical elements.
• the lens 114 is rotated around its axis.
• the beam splitter 106 may be moved along its plane; the minor 110 may be moved along its plane; the diffractive optic 113 may be moved in its plane, and the mirror/beam splitter 130 may be moved along its plane.
• the present invention may also be utilized to identify a rotation-induced laser induced wobble from a plurality of marks. Analysis of images of the marks may help account for these small deviations due to rotation of the optical element.
• FIG. 9 A simplified flowcharts illustrate a method for calibrating laser pulses employing the system of Fig. 1.
• the operator will begin by adjusting the illumination of the microscope camera 20 by turning the ring illumination setting to maximum and all other illuminations settings (e.g., reticle, oblique, and fixation lights) off.
• the chrome dot 36 is placed on a block coupled to the calibration arm 34.
• the microscope iris and magnification are also set.
• the image of the chrome dot 36 is then captured and the number of vertical and horizontal pixels of the dot image 36 calculated using an elliptical algorithm.
• the acceptable range for pixels in both directions is 420-460 and the values should be within 5% of each other. If this tolerance is not met, a failure message is indicated on the screen indicating that the image of the chrome dot 36 is out of range, not placed flat, or that the camera is misaligned and to start the procedure again. If the pixel tolerance is met, the pixel to mm ratio is determined using the vertical to horizontal pixel ratio of the dot image 36.
• the operator than replaces a calibration plastic 18, such as a silkscreen, for the chrome dot 36 and sets the laser energy for the calibration procedure between 180-220 mJ, preferably to 200-220 mJ, the spin integrator at 78580 counts, and the iris setting to 0.65 mm. All shutters and slits are open, the x and y positions are set to 0, and the forward/backward parameter is set to F.
• the iris setting is changed to 0.7 mm so that the iris is being opened (increasing laser beam diameter setting).
• Each mark or ablation is produced by firing 100 pulses at 20 Hz with a one second pause to allow any smoke to dissipate prior to capturing the image of the mark 28 with the camera 20.
• the capture image is rescaled according to the relative dimensions of the image of the known object 30 and fit to a circle algorithm so that the diameter of the laser beam may be precisely obtained. If the measured value is within 10% of the set/expected value, the iris size is changed to the next value larger than the previous ablation, and the above noted procedure repeated until the iris setting of 6.5 mm is reached.
• a warning message is indicated on the screen that there is an enor in the ablation image measurement.
• the procedure may be continued, but should be repeated upon completion.
• the same procedure is similarly repeated for decreasing laser beam diameter settings, wherein the iris setting is set to 6.7 mm so that the iris is being closed.
• the operator also receives a message on the screen to replace the calibration surface or to move it prior to imaging in the decreasing diameter setting mode.
• an acknowledgment by the operator may be required to ensure that a new silkscreen has been placed on the block.
• the integrator spinning will be stopped and the shutter closed.
• the relationship between laser beam diameter and motor counts associating the iris setting may then be determined from these two data sets, as previously discussed with reference to Figs. 8 A and 8B.
• the calibration system 10 of the present invention maybe applied to different laser systems, including scanning lasers and large area laser ablation systems.
• laser systems include the VISX STAR, STAR S2, STAR S3, STAR S4 Excimer Laser Systems, and laser systems employing wavefront technologies, all of which are commercially available from VISX, -Incorporated of Santa Clara, California.
• Other laser systems include those available from Alcon Summit, Bausch & Lomb, LaserSight, Zeiss Meditec, Schwind, Wavelight Technologies, and the like.

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