Patent Description:
Despite all the optimization of modern pre-surgical diagnostic and IOL formulas, about <NUM>% of cataract patients are left with visually significant refractive error after cataract surgery. This may include spherical power misses and also misses in matching existing higher order aberrations like chromatic aberrations. These misses -- the mismatches between the required optical power and the actual resulting optical power of the IOL -- can be corrected post cataract surgery by modifying the lens using a laser.

Post-surgical shape correction of the IOL by UV photo cross linking and the resulting shape change has been demonstrated and commercialized, for example, by RxSight, Inc.

<CIT> provides a lens for placement in a human eye, such as an intraocular lens, that can have at least some of its optical properties modified with a laser. The lens preferably contains at least <NUM>% by weight UV absorber so commercially feasible rates of manufacture can be achieved. The laser forms modified loci in the lens where the modified loci have a different refractive index than the refractive index of the material before modification.

The present invention provides a method, an ophthalmic surgical laser system, and a computer program product according to the independent claims. Embodiments are provided by the dependent claims. A method for forming a zone of a Fresnel-type gradient index lens in an implanted IOL is disclosed for illustrative purposes and does not form a part of the claimed invention.

An object of the present invention is to improve the processing speed of forming a Fresnel type gradient index lens in the IOL.

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 a method for forming a zone of a Fresnel type gradient index lens in an intraocular lens (IOL) before implantation of the IOL in the patient's eye, the zone having a ring shape and a predefined radial profile of optical pathlength (OPL) difference, the method including: scanning a pulsed laser beam in the IOL in multiple passes, wherein in each pass, the laser beam is scanned in concentric circles of varying radii within all of part of the zone, and wherein in each of all except a smallest one of the multiple passes, within a first radius range of the zone, the energy of the pulsed laser beam for each circle is below a predefined maximum energy and is dependent on the predefined radial profile of the OPL difference, and within a second radius range of the zone which is non-overlapping with the first radius range, the energy of the pulsed laser beam for each circle is the predefined maximum energy, and wherein in the smallest one of the multiple passes, within a first radius range of the zone, the energy of the pulsed laser beam for each circle is below the predefined maximum energy and is dependent on the predefined radial profile of the OPL difference.

In another aspect, the present invention is directed to an ophthalmic surgical laser system for forming a zone of a Fresnel type gradient index lens in an intraocular lens (IOL), the zone having a ring shape and a predefined radial profile of optical pathlength (OPL) difference, the system including: a laser light source configured to generate a pulsed laser beam; an optical delivery system configured to deliver the pulsed laser beam to the IOL, including a scanner system configured to scan the pulsed laser beam within the IOL; and a controller configured to control the laser light source and the scanner system to perform the above described method.

US publication number <CIT>, entitled Methods and Systems for Changing a Refractive Property of an Implantable Intraocular Lens ("the '<NUM> publication"), describes a "method of altering a refractive property of a crosslinked acrylic polymer material by irradiating the material with a high energy pulsed laser beam to change its refractive index. The method is used to alter the refractive property, and hence the optical power, of an implantable intraocular lens after implantation in the patient's eye. In some examples, the wavelength of the laser beam is in the far red and near IR range and the light is absorbed by the crosslinked acrylic polymer via two-photon absorption at high laser pulse energy. The method can be used to form a Fresnel lens in the optical zone [of the IOL]. " (Abstract. ) As described in the '<NUM> publication, the IOL may be formed of a crosslinked acrylic polymer, and the refractive index modification is achieved through heating of the material. The laser beam may be in the blue range, or the red and near infrared range, in which case the IOL material absorbs the laser light through two-photon absorption.

<FIG> schematically illustrates an ophthalmic surgical laser system <NUM> in which embodiments of the present invention can be implemented. The system <NUM>, which can project or scans an optical beam into a patient's eye <NUM> containing the IOL <NUM>, includes control electronics <NUM>, a laser light source <NUM>, an attenuator <NUM>, a beam expander <NUM>, focusing lenses <NUM>, <NUM> and reflectors <NUM>. Control electronics <NUM> may be a computer, microcontroller, etc. with memories storing computer-readable program code to control the operation of various components of the laser system to accomplish the scanning methods described herein. Scanning may be achieved by using one or more moveable optical elements (e.g. lenses <NUM>, <NUM>, reflectors <NUM>) which also may be controlled by control electronics <NUM>, via input and output devices (not shown). Another means of scanning might be enabled by an electro optical deflector device (single axis or dual axis) in the optical path. Although <FIG> shows the optical beam directed to a patient's eye, it should be understood that in the method of claim <NUM> the intraocular lens is irradiated before placement into the patient's eye in order to customize a refractive property of the intraocular lens. The system of claim <NUM> may be configured to perform this method once the IOL has been implanted in the patient's eye.

During operation, the light source <NUM> generates an optical beam <NUM> whereby reflectors <NUM> may be tilted to deviate the optical beam <NUM> and direct beam <NUM> towards the patient's eye <NUM> and particularly into the IOL in order to alter the refractive index of the IOL material. Focusing lenses <NUM>, <NUM> can be used to focus the optical beam <NUM> into the patient's eye <NUM> and the IOL. The positioning and character of optical beam <NUM> and/or the scan pattern it forms on the eye <NUM> may be further controlled by use of an input device such as a joystick, or any other appropriate user input device.

Although not shown in <FIG>, the laser system <NUM> preferably also includes imaging and visualization sub-systems, such as and without limitation, an optical coherence tomography (OCT) system, a video monitoring system, etc. These sub-systems are used to provide images of and to locate the various anatomical structures of the eye as well as the IOL, which can assist in performance of the various methods described later in this disclosure. Many types of imaging and visualization sub-systems are known in the art and their detailed descriptions are omitted here.

In many embodiments, the light source is a <NUM> to <NUM> pulsed laser source. In many embodiments, the light source <NUM> is a <NUM> to <NUM> laser source such as an tunable femtosecond laser system or it may be a Nd:YAG laser source operating at the 2nd harmonic wavelength, <NUM>, or 3rd harmonic wavelength, <NUM>.

In operation, the light of the light source is focused and is scanned in the IOL material in order to effect a change of the refractive index in a volume of the material. The shape and volume of the volume whose refractive index is changed is determined by the change in the refractive property of the intraocular lens that is desired.

In embodiments of the present invention, the IOL material is a crosslinked acrylic polymer, made of an optically clear, hydrophobic, acrylic elastomer. Without being limited by theory, one effect of the laser irradiation of the IOL material is to change the hydrophobicity of the acrylic material. As a result, water is expelled from the area in or around the area that has been irradiated, which causes or may cause a change in the refractive index of the material. Another effect of the laser irradiation is to cause local heating of the crosslinked acrylic polymer irradiated with the laser pulses, which causes or may cause a change in the refractive index of the material. The index change typically is proportional to total energy. In embodiments of the present invention, the wavelength of the laser beam is in the far red and near IR range and the light is absorbed by the IOL material via two-photon absorption at high laser pulse energy.

As described in the '<NUM> publication, by scanning the laser beam in the IOL in concentric patterns, concentric rings of refractive index variation may be generated, forming a Fresnel type gradient index lens. Such a lens may provide high optical power changes (by adding an optical power to the optical power of the IOL), as high as multiple diopters. <FIG> shows an example of a Fresnel refractive index profile along a radial direction from the lens center. The profile has multiple zones, where in each zone, the refractive index n ramps up and then jumps to the unchanged level. To be a Fresnel lens, the size of the jumps (the phase step) between zones should be equivalent to an integer number of waves. The refractive index difference may be expressed by the differences in optical path length (OPL) through the material, where OPL=n*s, s being the thickness of the relevant material (in a more complex case, the OPL is the integral of n over the light propagation path). The Fresnel profile requires the OPL difference to be: ΔOPL=Δn*s=Nλ, where N is an integer and λ is the wavelength of the light being refracted.

In the illustrated example, a layer of the IOL material approximately <NUM> thick is modified by the laser with a variable index in a number of annular zones (<NUM> in this case) centered on the optical axis of the IOL. Each zone has a <NUM> wave difference in OPL from the inner to the outer edge of the zone (which has a parabolic profile in this example), and a <NUM> wave step transitioning to the next zone. For example, a <NUM>-zone gradient index, Fresnel diffractive lens with a diameter of about <NUM>, has an optical power of <NUM> Diopters.

In practice, it may be difficult to achieve a refractive index change equivalent to a full wave of optical pathlength difference in the IOL by a single pulse of the laser beam. The use of femtosecond laser is a highly energy dependent process to achieve the index change within the material as it is based on multiphoton (e.g., two-photon) absorption. Due to the multiphoton absorption requirement, it is preferred that the system be used at the highest possible energy because the laser photons are more efficiently absorbed at higher energy levels than at lower energy levels. On the other hand, the upper end of useful energy is limited by the change of the process from an induced index change to an induced damage of the IOL material. For these reasons, the required refractive index change at a given location are typically not achieved in a single pass of the laser; rather, the intended pattern of refractive index change is achieved by repeated multiple (e.g., tens to hundreds) laser irradiations. In one method, the irradiation is repeated multiple consecutive times using the same patterns. For example, the laser beam is scanned along a circle at a particular radius for multiple times until the desired OPL difference is achieved.

Embodiments of the present invention uses a different scanning method, as illustrated in <FIG>. It does not scan the beam in the same pattern multiple consecutive times to add up to the desired OPL difference. Rather, as shown in <FIG>, to form a zone of a predefined OPL difference profile located between radii R1 and R0 (a zone is a ring shape in the plan view), the laser beam is scanned in multiple passes; in each pass, the laser beam is scanned in concentric circles of varying radii covering all or a part of the zone, with laser energy staying at a maximum energy Emax for most of the circles. The maximum energy is the highest allowed laser energy that can be applied to the IOL materials without causing damage to the IOL and/or the eye.

More specifically, as shown in <FIG>, in the first pass, the scanned circles cover the entire zone from R1 (one boundary of the zone with minimum or zero required OPL difference) to R0 (another boundary of the zone with maximum required OPL difference). Within the radius range from R1 to R2 (referred to as the ramp region), where the required OPL difference as determined by the predefined profile is below what can be achieved by one pass of laser irradiation at the maximum energy, the laser energy for each circle is set at a value that achieves the required OPL difference for that radius. Within the radius range from R2 to R0 (referred to as the maximum energy region), where the required OPL difference is above what can be achieved by one pass of laser irradiation at the maximum energy, the laser energy is set at the maximum energy. In other words, in this pass, the applied laser energy as a function of radius only makes one short ramp to the maximum energy and then stays constant at the maximum energy until the phase step boundary R0 is reached. The location of R2 (the dividing radius between the ramp region and the maximum energy region) is determined by the profile shape of the zone and the OPL difference produced by the maximum energy. Note the scan can alternatively proceed from R0 to R1. The shaded trapezoidal shape in <FIG> represents the OPL change achieved by the first pass.

The next (second) pass skips (i.e., does not scan) the region where the first pass applied the energy ramp (i.e., between R1 and R2), and starts ramping just where the ramp of the previous (first) pass stopped (i.e. at R2). For the second pass, within the radius range from R2 to R3, where the remaining required OPL difference -- i.e., the OPL difference required by the predetermined profile minus the OPL difference that has been achieved by the previous passes (the first pass) -- is below what can be achieved by one pass of laser irradiation at the maximum energy, the laser energy for each circle is set at a value that achieves the remaining required OPL difference for that radius. Within the radius range from R3 to R0, where the remaining required OPL difference is above what can be achieved by one pass of laser irradiation at the maximum energy, the laser energy is set at the maximum energy. Thus, again, a short ramp to the maximum energy is applied and then the energy stays constant at the maximum energy until the phase step boundary R0 is reached. The scan can alternatively proceed from R0 to R2.

Additional passes are performed in a similar manner, consecutively, until the desired full step height of OPL difference is reached at radius R0.

To summarize, the parameters of the multiple passes within a zone may be defined as follows. The zone is a ring shaped area between two phase step boundaries at radius R0 and radius R1. An OPL difference profile desired to be achieved, ΔOPL, is a function of radius defined in the zone, where ΔOPL is zero at R1 and is a predefined maximum value ΔOPLmax at R0, and varies monotonously in between. A number of additional radii R2, R3,. Rm are defined consecutively between R1 and R0, where each Ri (i=<NUM>, <NUM>,. , m) is the radius at which the ΔOPL profile has a value that is a multiple of ΔOPLe, or more specifically, ΔOPLe*(i-<NUM>), where ΔOPLe corresponds to the OPL difference produced by one pass of the laser scan at the maximum energy Emax.

The multiple scan passes are performed between R0 and the respective radii R1, R2,. , Rm, e.g., the i-th pass is performed between R0 and Ri (i=<NUM>, <NUM>, <NUM>,. In each pass, the laser beam is scanned in concentric circles of varying radii from R0 to Ri (or from Ri to R0). Each pass except for the smallest pass, e.g., the i-th pass (i=<NUM>, <NUM>, <NUM>,. , m-<NUM>), has two regions: a ramp region defined as the radius range from Ri to Ri+<NUM>, and a maximum energy region defined as the radius range from Ri+<NUM> to R0. The smallest pass, between R0 and Rm, has only a ramp region and no maximum energy region. Within the ramp region of each pass, the laser energy for each circle is set at a value that produces an OPL difference of (ΔOPLr mod ΔOPLe), or more specifically, (ΔOPLr - ΔOPLe*(i-<NUM>)), where ΔOPLr is the value of the ΔOPL profile at the radius r of that circle, and mod is the modulo operation. Within the maximum energy region of each pass, the laser energy is set at the maximum energy Emax. For each pass except for the largest pass (R1 to R0), the region of the zone between R1 and Ri is a skip region where no laser beam is applied.

From the above descriptions, it can be seen that the ramp regions of all of the passes are non-overlapping with each other and collectively cover the entire zone from R1 to R0, and that the second radius ranges of all except the smallest pass partially overlap each other.

Using this scanning method, radial laser passes have the laser set at the maximum laser energy for much of each pass, which enables highly efficient laser processing at the most efficient energy set point.

In the example shown in <FIG>, the predefined OPL difference profile of the zone is shown as being approximately linear. However, the method is applicable to all possible shapes of OPL difference profiles required to be achieved so long the profile is monotonic in the zone. For example, the profile of the zone may be parabolic as shown in the example of <FIG>, or a free form profile, etc. The boundary locations (e.g. R2, R3, etc.) between the ramp region and the maximum energy region for each pass is determined by the profile shape and the OPL difference produced by the maximum laser energy.

In some embodiments, for scanned circles belonging to different passes that are located at the same radius, the laser focus positions may be shift slightly in the circumferential direction (e.g., angular direction) so they do not overlap, to avoid overdelivering laser energy in one focal area. This is advantageous particularly in areas that require a high number of passes. It allows a more uniform distribution within the IOL material and avoids possible damage due to multiple laser focus spots overlapping.

The depth of each scan pattern may also be adjusted to correct a focus depth shift effect due to multiphoton absorption. In multiphoton absorption, due to the high beam energy, the location where absorption occurs may shift away from the intended focus spot of the laser beam and toward the incident beam. This is caused by the energy of the laser pulse being absorbed and even depleted shortly before it reaches the intended focus spot due to the onset of two-photon absorption in the volume in front of the focus, as the power density becomes sufficiently high in that volume due to focusing and exceeds the threshold of two-photon absorption. Thus, in the above described scanning method, the depth location of beam absorption may be different when the applied laser energy is different. In some embodiments of the present invention, to compensate for such differences in the beam absorption locations, the intended focus position of the beam may be dynamically adjusted accordingly, to ensure that the planned effect depth is achieved for all beam energies.

In some embodiments, the variation of laser energy of the scans in the ramp regions is accomplished by varying the energy per pulse of the laser beam. In an alternative embodiment, the variation of laser energy in the ramp regions may be achieved by utilizing variable laser spot spacing of the scanned circles, either alone or in combination with varying the pulse energy of the incident laser pulses. Larger lateral spacing (lower spot density) will lead to lower refractive index change per unit area, while higher spot density will lead to higher refractive index change per unit area.

In some alternative embodiments, the various passes may be carried out in other orders. For example, referring again to <FIG>, if the passes are designated 1st, 2nd, 3rd,. nth which cover successively narrower rings of the profile zone (i.e., with successively larger skip regions), the passes may be performed in the order of 1st, nth, 2nd, (n-<NUM>)th, 3rd, (n-<NUM>)th,. This orders allows for additional effective space in between the different passes. Other orders are also possible.

Although the scan pattern are described above as being circles, they may alternatively be ellipses or arcs (i.e. parts of full circles), and the ring shaped zone may correspondingly be elliptical shaped or be an angular segment of a circular ring.

In the above-described scanning method, the multiple scanning passes may be performed at the same depth of the IOL material, or at slightly different depths. Because the OPL of a given light propagation path is the integral of the refractive index over the distance, the total OPL difference at each radius is the same regardless of whether the multiple scanning passes occur at the same depth or slightly different depths. Thus, in some embodiments, a spatial depth separation may be introduced to the different passes. In preferred embodiments, the different passes are performed at substantially the same depth, except for possible focus depth shift effect due to multiphoton absorption.

Using various embodiments of the present invention, much higher processing efficiency can be achieved which make the application more practicable in a patient's eye. The method highly increases the processing speed and makes the application usable in a treatment environment.

Claim 1:
A method for forming a zone of a Fresnel type gradient index lens in an intraocular lens, IOL, before placement into a patient's eye, the zone (R0-R1) having a ring shape and a predefined radial profile of optical pathlength, OPL, difference, the method comprising:
scanning a pulsed laser beam (<NUM>) in the IOL in multiple consecutive passes,
wherein in each pass, the laser beam (<NUM>) is scanned in concentric circles of varying radii within all or part of the zone, characterised in that
in each of all except a smallest one of the multiple passes, within a first radius range of the zone, an energy of the pulsed laser beam for each circle is below a predefined maximum energy and is dependent on the predefined radial profile of the OPL difference, and within a second radius range of the zone which is non-overlapping with the first radius range, the energy of the pulsed laser beam for each circle is the predefined maximum energy, and
wherein in the smallest one of the multiple passes, within a first radius range of the zone, the energy of the pulsed laser beam (<NUM>) for each circle is below the predefined maximum energy and is dependent on the predefined radial profile of the OPL difference.