Patent Application
20220062049
This invention relates to forming corneal incisions using ultra-short pulsed laser, and in particular, it relates to forming deep lamellar incisions parallel to the posterior corneal surface and a posterior corneal surface mapping method.
Deep anterior lamellar keratoplasty (DALK) is a corneal transplant technique. It cuts and removes an anterior corneal button from the recipient eye, then replaces it with an anterior corneal button cut from a donor cornea. Ultra-short pulsed laser systems, such as femtosecond lasers, has been applied to this procedure. In conventional DALK techniques, the deep lamellar incision profile, for example, a planar dissection, is typically set to be parallel to the surface of the patient interface device (a device used to engage and restrain the patient's eye during ophthalmic procedures), as schematically illustrated in
Methods have also been described which set the corneal dissection profile in parallel to the posterior corneal surface when cutting a corneal button, for example, in U.S. Pat. Appl. Pub. No. 20070027438, entitled “System and method for compensating a corneal dissection,” and U.S. Pat. No. 10,080,684, entitled “System and method for laser corneal incisions for keratoplasty procedures.” These references describe measuring the topology of the cornea, including the posterior corneal surface, using methods such as wavefront analysis of the reflected diagnostic beam, ellipsometry, second harmonic generation (SHG) microscopy, confocal microscopy, corneal topography, optical coherence tomography (OCT), or ultrasonic pachymetry, Purkinje imaging, Scheimpflug imaging, confocal or nonlinear optical microscopy, fluorescence imaging, ultrasound, structured light, or stereo imaging (see US 20070027438 , ¶[0034], and U.S. Pat. No. 10,080,684, col. 17, lines 14-28). In these references, the anterior cornea surface of the eye is not shown as being applanated by the surface of the patient interface device (see, e.g., FIG. 4B of US 20070027438 and FIG. 5A of U.S. Pat. No. 10,080,684).
Embodiments of the present invention are directed to a method for forming deep corneal lamellar incision that is parallel to the posterior corneal surface, in which a lower-energy detecting beam generated by the same pulsed laser that generates the higher-energy treatment laser beam is utilized to measure the posterior corneal surface profile when the eye is docked to the patient interface.
Additional features and advantages of the invention will be set forth in the descriptions that follow and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims thereof as well as the appended drawings.
To achieve the above objects, the present invention provides an ophthalmic laser system that includes: a pulsed laser configured to generate a pulsed laser beam; an optical system including an objective lens and one or more scanners, configured to focus the laser beam to a focus point and to scan the focus point in three directions in an eye of a patient; a light intensity detector disposed to detect a light intensity of a back-reflected laser beam from the eye that has passed through the objective lens; a controller electrically coupled to the pulsed laser, the optical system and the light intensity detector, wherein the controller is configured to: control the pulsed laser to generate a first laser beam having a first pulse energy lower than a threshold energy for photodisruption of corneal tissue; control the optical system to scan the focus point of the first laser beam according to a first scan pattern, wherein the first scan pattern is at least partially located within a cornea of the eye and extends in a predetermined depth range in a depth direction which is parallel to an optical axis of the objective lens; control the detector to detect a light intensity signal of a back-reflected portion of the first laser beam while the focus point of the first laser beam is scanned according to the first scan pattern; based on a correspondence between the light intensity signal and the first scan pattern, determine a depth profile of a posterior corneal surface of the eye; control the pulsed laser to generate a second laser beam having a second pulse energy higher than the threshold energy; and based on the determined depth profile of the posterior corneal surface, control the optical system to scan the focus point of the second laser beam within the cornea according to a second scan pattern, the second scan pattern having a defined spatial relationship with the determined posterior corneal surface profile, to form an incision in the cornea.
In some embodiments, the one or more scanners includes a Z scanner and an X-Y scanner, and the controller is configured to scan the focus point of the first laser beam according to the first scan pattern by: controlling the Z scanner to scan the focus point in the depth direction according to an oscillating function of time; and simultaneously controlling the X-Y scanner to scan the focus point in a spiral pattern in a plane perpendicular to the depth direction.
In some embodiments, the one or more scanners includes a Z scanner, an X-Y scanner, and a resonance scanner, and the controller is configured to scan the focus point of the first laser beam according to the first scan pattern by: controlling the Z scanner to scan the focus point in the depth direction according to a oscillating function of time; simultaneously controlling the X-Y scanner to scan the focus point in a spiral pattern in a plane perpendicular to the depth direction; and simultaneously controlling the resonant scanner to scan the focus point into a scanline in the plane at a frequency higher than a frequency of the oscillating function of the Z scanner.
In some embodiments, the one or more scanners includes a Z scanner, an X-Y scanner, and a resonance scanner, and the controller is configured to scan the focus point of the first laser beam according to the first scan pattern by: controlling the Z scanner and the X-Y scanner to scan the focus point in three dimensions according to a pattern; and simultaneously controlling the resonant scanner to scan the focus point into a scanline in a plane perpendicular to the depth direction.
In another aspect, the present invention provides an ophthalmic laser surgery method implemented in an ophthalmic laser system, which includes: coupling an eye of a patient to a patient interface device of the ophthalmic laser system; while the eye is coupled to the patient interface: by a laser source of the ophthalmic laser system, generating a first laser beam having a first pulse energy lower than a threshold energy for photodisruption of corneal tissue; by an objective lens, focusing the first laser beam to a focus point; by one or more scanners of the ophthalmic laser system, scanning the focus point of the first laser beam according to a first scan pattern, wherein the first scan pattern is at least partially located within a cornea of the eye and extends in a predetermined depth range in a depth direction which is parallel to an optical axis of the objective lens; by a light intensity detector of the ophthalmic laser system, detecting a light intensity signal of a back-reflected portion of the first laser beam while the focus point of the first laser beam is scanned according to the first scan pattern; by a controller of the ophthalmic laser system, based on a correspondence between the light intensity signal and the first scan pattern, determining a depth profile of a posterior corneal surface of the eye; by the pulsed laser, generating a second laser beam having a second pulse energy higher than the threshold energy; by the objective lens, focusing the second laser beam to a focus point; and by the one or more scanners, based on the determined depth profile of the posterior corneal surface, scanning the focus point of the second laser beam within the cornea according to a second scan pattern, the second scan pattern having a defined spatial relationship with the determined posterior corneal surface profile, to form an incision in the cornea.
In some embodiments, the step of scanning the focus point of the first laser beam according to the first scan pattern includes: by a Z scanner of the ophthalmic laser system, scanning the focus point in the depth direction according to an oscillating function of time; and simultaneously, by an X-Y scanner of the ophthalmic laser system, scanning the focus point in a spiral pattern in a plane perpendicular to the depth direction
In some embodiments, the step of scanning the focus point of the first laser beam according to the first scan pattern includes: by a Z scanner of the ophthalmic laser system, scanning the focus point in the depth direction according to an oscillating function of time; simultaneously, by an X-Y scanner of the ophthalmic laser system, scanning the focus point in a spiral pattern in a plane perpendicular to the depth direction; and simultaneously, by a resonant scanner of the ophthalmic laser system, scanning the focus point into a scanline in the plane at a frequency higher than a frequency of the oscillating function of the Z scanner.
In some embodiments, the step of scanning the focus point of the first laser beam according to the first scan pattern includes: by a Z scanner and an X-Y scanner of the ophthalmic laser system, scanning the focus point in three dimensions according to a pattern; and simultaneously, by a resonant scanner of the ophthalmic laser system, scanning the focus point into a scanline in a plane perpendicular to the depth direction.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.
Embodiments of the present invention describes a method that utilizes a detecting laser beam, generated by the same pulsed laser that generates the higher-energy treatment laser beam, to measure the posterior corneal surface profile, and to form a deep corneal lamellar incision parallel to the measured posterior corneal surface. Because a beam from the same pulsed laser that generates the treatment beam is used to measure the posterior corneal surface profile, calibration error is significantly reduced or eliminated. This is more advantageous than using the optical coherence tomography (OCT) technique to measure the posterior corneal surface, as OCT uses a light beam not generated by the treatment laser. The method described here has a precision of approximately 1 μm, which is higher than that of the OCT technique (approximately 10 μm). This higher precision is advantageous for performing deep incisions close to the posterior corneal surface.
To form a deep lamellar corneal incision parallel to posterior corneal surface, first, the patient's eye is docked to the patient interface device (
The principles of depth measurement is described below with reference to
The objective lens 34 is mounted on a movement structure and moveable in the Z direction (parallel to the optical axis) relative to a housing of the laser system, so as to focus the laser beam at desired depths and to vary the depth of the focus spot. The movement structure may include any suitable mechanical structure, such as a translation stage driven by a motor, etc.
A part of the laser light that exits the objective lens 34 is reflected by a reflective (including partially reflective) interface 101 located below the objective lens 34, and the reflected light travels backwards into the objective lens 34. After the back-reflected light is focused by the objective lens 34 and reflected by the mirror 33, a part of the reflected light is reflected by the beam splitter 32 onto a small two-dimensional light intensity detector 37 (e.g. a photodetector). In the illustrated embodiment, no confocal lens or pinhole is used in front of the detector 37.
The reflective interface 101 is an interface whose depth is being measured. In this embodiment, the reflective interface is the posterior corneal surface, but it can be any reflective interface, including, for example, a surface of contact lens of the patient interface, and the depth measurement principle described below applies equally. In
A controller 40 controls the operations of the laser source 31, objective lens 34, and detector 37. The controller may be implemented by electrical circuitry including logic circuits, and/or processors which execute computer executable program code stored in computer readable non-volatile memories.
The principle of Z position measurement using the laser system of
F with respect to the reflective interface 101. The distance from the equivalent origin B to the objective lens 34 is u=f+2δ (Equation (1)), where δ=FA is the offset distance between the focus point F and the reflective interface 101. The reflected light from the equivalent origin B is focused by the objective lens 34 to an image point D at a finite distance v from the objective lens. The detector 37 is located at the image point D, and no other lens is disposed between the objective lens 34 and the detector 37.
Using Equation (1) and the following lens formula for a thin lens (Equation (2)),
where u is the object distance and v is the image distance, one obtains (Equation (3)):
When f is much smaller than v (discussed later), one obtains (Equation (4)):
The above equations are for focusing in the air. When the focus point F is located inside an optical medium (e.g. the cornea), the refractive index n of the optical medium is taken into consideration, and one obtains (Equation (5)) (note here that the refractive index n is an effective index of the optical system which has multiple components and different materials):
It should be understood that in the above equations, the various distances are the distances along the optical path; the optical path may be folded by mirrors or beam splitters.
In the laser system 30, the distance DO from the detector 37 to the objective lens 34 (i.e. the imaging distance v) is approximately a device constant, because the location of the detector 37 is fixed relative to the laser system housing and the amount of focusing movement of the objective lens 34 with respect to the housing is much smaller than the distance DO. Therefore, the distance δ given by Equation (5) is approximately a constant of the laser system 30. The point located at distance δ before the reflective interface 101 is referred to as the target focus position for convenience. If the light is focused by the objective lens 34 at this target focus position, the reflected light from the reflective interface 101 will be focused onto the detector 37.
In some embodiments, the focal distance f, i.e. the equivalent focal length of the objective lens 34, is a few mm, e.g. approximately 4 mm. Meanwhile, the distance DO from the detector 37 to the objective lens 34 may be several hundreds of mm (e.g. 500 mm), because the choice of the detector location is not constrained and the image distance v may be lengthened if desired by folding the optical path with mirrors. Therefore, f is much smaller than v (by a factor on the order of 100). In one particular embodiment, where the image distance v (DO) is approximately 500 mm and the equivalent focal length f is 3.92 mm, using the refractive index of the optical medium (cornea) of n=1.38, Equation (5) gives δ≈21 μm.
When the objective lens 34 focuses the laser beam at positions other than the target focus position defined by 6, the back-reflected light will not be focused on the detector 37 located at point D, but will be focused before it, after it, or not be focused at all.
To summarize, the back-reflected light from the reflective interface 101 will only form a well focused real image on the detector 37 when the objective lens 34 focuses the parallel beam to the target focus position defined by δ (Equation (5)). The detector 37 has a relatively small effective detection area, such as about 1 mm2 or smaller. Having a small effective detection area refers to the detector either having a physically small detection area or being controlled to detect light falling within a small area. As a result, when the back-reflected light is not focused on the detector, substantial portions of the reflected light will not fall on the effective detection area and the detected light intensity will decrease significantly. Therefore, the light intensity signal detected at the detector 37 (referred to as the auto-Z signal) peaks when the objective lens focuses the parallel laser beam to the target focus position. Thus, by continuously moving the objective lens 34 in the Z direction and continuously detecting the auto-Z signal, the target focus position can be measured (e.g., as expressed by the corresponding position of the objective lens); from the target focus position, the Z position of the reflective interface 101 can be obtained using the value of δ.
A calibration process may be carried out by using the above technique to measure the Z position of a reference surface, for example, the distal surface of the patient interface lens. In the calibration process, the laser beam is focused at a distance δ before the reference which acts as the reflective interface 101. After such calibration, the Z position of the posterior corneal surface may be expressed as a distance relative to the reference surface.
The technique described above can achieve a 1 μm or higher depth resolution of the Z position detection.
The above depth measurement technique is also described in commonly owned, co-pending application U.S. Pat. Appl. No. 16/112507, filed Aug. 24, 2018, entitled “Detection of optical surface of patient interface for ophthalmic laser applications using a non-confocal configuration,” the disclosure of which is incorporated by reference in its entirety. U.S. Pat. No. 16/112507 also describes a method of empirically measuring the value of the offset distance δ for a given laser system, without using Equation (5).
Referring to
Referring to
In an alternative embodiment of the depth measurement method, step S62 is modified as follows. For each X-Y position, at a given depth, the laser focal spot is scanned, preferably at high speed, over a small area in the X-Y plane centered at the given X-Y position. The auto-Z signal measured during such X-Y scan (in step S63), at the given depth, is an integrated signal from the scanned area . The depth measured by such integrated auto-Z signal represents the average depth of the corneal posterior surface corresponding to the scanned area. A resonant scanner, described in more detail later, may be used to perform such X-Y scan by scanning the focal spot into a short scanline of, for example, about 100 μm long (more generally, between 50 and 200 μm). This alternative method reduces laser exposure at a given tissue location, because the laser spot is spread out while the auto-Z signal is integrated.
Another embodiment of the method for obtaining a posterior corneal surface profile (step S52 of
A three-dimensional scan is then executed using the resonant scanner, a fast-Z scanner, and the X-Y scanner of the laser source 31 operating simultaneously (step S94). The fast-Z scanner scans the depth of the focal spot as a sinusoidal function (or other oscillating function) of time at an amplitude of about 100 μm (or more generally, at an amplitude between 10 um and 100 μm) (see
In one example, the fast-Z scan frequency is about 10 Hz and the linear speed of the X-Y scan is approximately 45 mm/s. Using these parameters, a depth mapping may be performed within 2 seconds resulting in 40 measured data points along a spiral of 90 mm in linear length. This is typically sufficient to reconstruct a depth profile of the posterior corneal surface. More generally, the fast-Z scan frequency may be from 10 to 40 Hz and the X-Y scan speed may be from 10 to 45 mm/s.
While a spiral pattern is shown in
An advantage of the posterior corneal surface mapping methods described here is that the measurement beam is the same as the cutting beam except for the lower pulse energy; therefore, position calibration in X, Y and Z directions between the measurement tool and the cutting laser beam is always precisely maintained. This is not the case when OCT is used to perform posterior corneal surface mapping.
Once the posterior corneal surface profile is measured, the laser pulse energy is set to a treatment level (e.g., approximately 70 nJ, or more generally, between 40 and 90 nJ), and a deep lamellar incision may be made using the treatment laser beam, where the lamellar incision is parallel to and located at a predetermined distance from the posterior corneal surface (see
Note that the lamellar incision is not always required to be parallel to the posterior corneal surface. In alternative embodiments, the distance between the lamellar incision and the posterior corneal surface may vary with the X-Y position. More generally, once the posterior corneal surface profile is measured, the lamellar incision may be formed so that it has any defined spatial relationship with the posterior corneal surface.
The laser source 31 that may be used to implement the above-described methods is described in more detail now with reference to
The resonant scanner 3 scans the pulsed laser beam at a high resonant frequency (e.g., thousands of Hz) to produces the scan line that extends in a lateral orientation (i.e. a direction perpendicular to the laser beam propagation direction Z) and having a desired length, for example, between 1 mm and 2 mm. The length of the scan line may be adjustable. The scan line rotator 4 may be implemented by a Dove prism, a Pechan prism, a set of mirrors, or the like, mounted on a rotating stage. By rotating the scan line rotator 4 around the Z axis, the lateral orientation of the scan line 12 is rotated, so that the scan line may be placed at any desired orientation in the XY plane (i.e., the lateral plane perpendicular to the laser beam propagation direction Z). The XY scan device 7 may be a movable XY scanning stage having the focusing objective 6 mounted thereon; the XY scan device 7 carries the objective 6 and moves it relative to the patient interface device 9, so as to move the center of the scan line 12 relative to the patient's eye in the XY directions. The fast-Z scan device 8 changes the depth (i.e. along the Z direction) of the laser focal spot location in the eye. Thus, the scan line rotator 4 modifies the lateral orientation of the scan line 12 while the moveable XY scanning stage 7 and the fast-Z scan device 8 move the center of the scan line in X, Y and Z directions. Because the scanning speed of the resonant scanner is typically much faster than the speed of the XY scanning stage and the fast-Z scan device, the scan line 12 may be referred to as a fast scan line, and the movement of the fast scan line in X, Y and Z directions may be referred to as a slow sweep.
The XY scanning stage 7 may be a motorized stage with two motors that drive its movements in the X and Y directions. Preferably, the XY scanning stage is a recoilless stage configured to reduce or eliminate mechanical vibration. The fast-Z scan device 8 may include a voice coil actuator that drives a lens in the Z direction. Movements of the lens lead to a focus depth change. The z-scan frequency may be between 50 Hz and 15,000 Hz.
The patient interface device 9 couples the patient's eye to the ophthalmic surgical laser system 1. The patient interface 9 may include a visualization beam splitter to reflect the light from the eye along an optical path 11 toward a video microscope or ocular microscope 14, to allow the eye to be imaged by an image detector of the microscope.
The auto Z module 10 may be either a confocal detector or a non-confocal detector.
The controller 13, which may be implemented by a processor executing suitable machine-readable program code and data stored in a non-volatile memory, is operably coupled to the various components of the system 1 including the laser 2, the fast-Z scan device 8, the resonant scanner 3, the scan line rotator 4, the XY scanning stage 7, the detector 14, and the communication module 15. The controller 13 is configured to direct these components of the system to output the focal spot of the pulsed laser beam in a desired pattern in the eye so as to modify the eye. The communication module 15 provides information to the operator of the laser system 1 at the system and/or remotely via wired or wireless data connection, and may include displays, user input devices such as keyboard, mouse, joystick, etc. The ophthalmic surgical laser system may additionally include an OCT (optical coherence tomography) device (not shown in
One difference between the embodiment of
The controller 13 or 13B may correspond to the controller 40 in
Further details of ophthalmic surgical laser systems having the configurations shown in
In other embodiments, an ophthalmic surgical laser system may employ other types of scanners, such as two orthogonal scanning mirrors, for scanning the laser beam in the transverse (XY) directions. Many such systems are known and their details are not described here.
While specific reference is made to keratoplasty and ophthalmic procedures, the embodiments described herein can be used in other applications for improved tissue incisions with decreased irregularity of the incised tissue surface, as well as for more accurate tissue cutting with improved healing. Among other things, these additional applications include mapping anterior or posterior crystalline lens surface when performing incisions in the crystalline lens. The method may be used more generally as a tool for high precision corneal pachymetry. It may also be used to profile corneal defects such as internal scars within the cornea. More generally, the method is applicable as a measurement tool in any transparent material where a reflective interface is present.
It will be apparent to those skilled in the art that various modification and variations can be made in the posterior corneal surface mapping and deep lamellar corneal incision methods and related apparatus of the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover modifications and variations that come within the scope of the appended claims and their equivalents.
This application claims the benefit under 35 U.S.C. § 119(e) of U.S. Provisional Patent Application No. 63/072066, filed Aug. 28, 2020, which is incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 63072066 | Aug 2020 | US |
