Patent Grant
11793675
Cataract extraction is one of the most commonly performed surgical procedures in the world. A cataract is the opacification of the crystalline lens or its envelope—the lens capsule—of the eye. It varies in degree from slight to complete opacity that obstructs the passage of light. Early in the development of age-related cataract the power of the lens may be increased, causing near-sightedness (myopia), and the gradual yellowing and opacification of the lens may reduce the perception of blue colors as those wavelengths are absorbed and scattered within the crystalline lens. Cataract typically progresses slowly to cause vision loss and are potentially blinding if untreated.
Treatment is performed by removing the opaque crystalline lens and replacing it with an artificial intraocular lens (IOL). An estimated 3 million cases are presently performed annually in the United States and 15 million worldwide. This market is composed of various segments including intraocular lenses for implantation, viscoelastic polymers to facilitate surgical maneuvers, disposable instrumentation including ultrasonic phacoemulsification tips, tubing, and various knives and forceps.
However, post-surgical visual acuity in patients with a newly implanted IOL is often imperfect. There is a need for improved methods of correcting the refractive properties of an IOL after implantation in order to improve post-surgical outcomes.
In many embodiments, a method of altering a refractive property of a crosslinked acrylic polymer comprises generating a light beam with a light source; and irradiating the crosslinked acrylic polymer with the light beam, thereby producing a predetermined change in a refractive property of the crosslinked acrylic polymer. Preferably, irradiation with the laser light beam results in a change in refractive index of the cross-linked acrylic polymer, thereby causing the predetermined change in the refractive property. In many embodiments, a first change in the refractive index is negative during a first time period after irradiation and a second change in the refractive index is positive in a second time period after irradiation. In many embodiments, a change in refractive index of the cross-linked acrylic polymer relative to the pre-irradiation refractive index at a location within the crosslinked acrylic polymer is linearly related with a total energy of the irradiation with the light source.
In preferred embodiments, the light source is a pulsed laser source, and the pulsed laser source produces femtosecond or longer up to a few nanosecond laser pulse. In preferred embodiments, the pulsed laser pulses irradiate the crosslinked acrylic polymer and produce a first change in the refractive index which is negative during a first time period after irradiation and a second change in the refractive index which is positive in a second time period after irradiation. The first time period may occur either before or second time period, i.e. the change may be negative and then becomes positive, or vice versa. This predetermined change in refractive index relative to the pre-irradiation refractive index at a location within the crosslinked acrylic polymer is determined by controlling a total energy of the irradiation with the light source.
A method of altering a refractive property of an implantable intraocular lens having an optic body including an optical zone and a peripheral zone entirely surrounding the optical zone, comprises generating a light beam with a light source; and irradiating the optical zone with the light beam. The optical zone comprises a crosslinked acrylic material and irradiation with the light beam produces a predetermined change in a refractive property of the crosslinked acrylic polymer, thereby altering a refractive property of the intraocular lens. Preferably, irradiation with the laser light beam results in a change in refractive index of the cross-linked acrylic polymer, thereby causing the predetermined change in the refractive property. Preferably, first change in the refractive index is negative during a first time period after irradiation and a second change in the refractive index is positive in a second time period after irradiation, and becomes stable over a long period of time. Preferably, the change in refractive index relative to the pre-irradiation refractive index at a location within the crosslinked acrylic polymer is linearly related with a total energy of the irradiation with the light source.
In another aspect, the present invention provides a method of altering a refractive property of an implantable intraocular lens having an optic body including an optical zone and a peripheral zone surrounding the optical zone, the method including: generating a light beam using a light source and a light delivery optical system; and irradiating the optical zone with the light beam, wherein the optical zone comprises a material configured to change its refractive index upon irradiation by the light beam, thereby altering a refractive property of the intraocular lens.
In some embodiments, the optical zone comprises a crosslinked acrylic material, and wherein irradiation with the light beam produces a predetermined change in the refractive index of the crosslinked acrylic polymer. In some embodiments, the intraocular lens is implanted in a patient's eye before the irradiating step, and the light beam with a wavelength of 400 to 450 nm or 650 to 800 nm is used.
In some embodiments, the light source is a pulsed laser source, and irradiating step includes scanning a focus spot of the pulsed laser beam within the optical zone of the intraocular lens according to a scan pattern. In some embodiment, the scan pattern is designed to compensate for a multi-photon absorption-induced shift in absorption depth. In some embodiments, the scan pattern is designed to compensate for a thermal lensing effect, which is an optical effect on subsequent laser pulses caused by a temperature gradient induced by previous laser pulses. In some embodiments, the scan pattern includes forming a plurality of layers (or lines, or spots) in an interlaced manner such that any layers that are immediately adjacent each other in their spatial order are not immediately adjacent each other in the time order in which they are formed. In some embodiments, the scan pattern in the optical zone is configured to produce a refractive index modification profile of a Fresnel lens.
This summary and the following detailed description are merely exemplary, illustrative, and explanatory, and are not intended to limit, but to provide further explanation of the invention as claimed. Additional aspects, features, objectives and advantages of the invention will be set forth in the descriptions that follow, and in part will become apparent from the written description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention, or may be learned by practice of the invention.
In many embodiments, a method of altering a refractive property of a crosslinked acrylic polymer comprises generating a light beam with a light source; and irradiating the crosslinked acrylic polymer with the light beam, thereby producing a predetermined change in a refractive property of the crosslinked acrylic polymer. Preferably, irradiation with the laser light beam results in a change in refractive index of the cross-linked acrylic polymer, thereby causing the predetermined change in the refractive property. In some embodiments, a first change in the refractive index is negative during a first time period after irradiation and a second change in the refractive index is positive in a second time period after irradiation. In some embodiments, a change in refractive index of the cross-linked acrylic polymer relative to the pre-irradiation refractive index at a location within the crosslinked acrylic polymer is linearly related with a total energy of the irradiation with the light source.
In preferred embodiments, the light source is a pulsed laser source, and the pulsed laser source produces at least one of femtosecond laser pulse and picosecond laser pulses. In the preferred embodiments, the pulsed laser pulses irradiate the crosslinked acrylic polymer and produce a first change in the refractive index is negative during a first time period after irradiation and a second change in the refractive index is positive in a second time period after irradiation. The first time period may occur either before or second time period. The predetermined change in refractive index relative to the pre-irradiation refractive index at a location within the crosslinked acrylic polymer is determined by controlling a total energy of the irradiation with the light source.
A method of altering a refractive property of an implantable intraocular lens having an optic body including an optical zone and a peripheral zone entirely surrounding the optical zone, comprises generating a light beam with a light source; and irradiating the optical zone with the light beam. The optical zone comprises a crosslinked acrylic material and irradiation with the light beam produces a predetermined change in a refractive property of the crosslinked acrylic polymer, thereby altering a refractive property of the intraocular lens. Preferably, irradiation with the laser light beam results in a change in refractive index of the cross-linked acrylic polymer, thereby causing the predetermined change in the refractive property. Preferably, first change in the refractive index is negative during a first time period after irradiation and a second change in the refractive index is positive in a second time period after irradiation. Preferably, the change in refractive index relative to the pre-irradiation refractive index at a location within the crosslinked acrylic polymer is linearly related with a total energy of the irradiation with the light source.
Preferably, the light source is a pulsed laser source. The pulsed laser source produces femtoseconds or longer up to a few nanoseconds laser pulses. A first change in the refractive index caused by irradiation with the pulsed laser is negative during a first time period after irradiation and a second change in the refractive index is positive in a second time period after irradiation. Preferably, the change in refractive index relative to the pre-irradiation refractive index at a location within the crosslinked acrylic polymer is linearly related with a total energy of the irradiation with the light source.
One embodiment of an intraocular lens suitable for use in connection with the present invention is shown in
As illustrated in
The optic body 11 is preferably generally circular having a radius Ro and is typically constructed of deformable-elastic transparent lens body of crosslinked acrylic material having a tensile strength sufficient to resist deformation after implantation into the eye as by forces exerted by growing tissue around the IOL; a flexibility as measured by elongation at break sufficient to allow the lens body to be readily folded, rolled or otherwise deformed to a low profile condition for implantation through a small incision into the eye; an elastic memory which enables the folded lens body to naturally and at a controlled rate return to its original shape and optical resolution without damaging or otherwise traumatizing eye tissue; and a low-tack surface which will not stick to surgical instruments used to hold and guide the lens body during insertion and positioning within the eye.
In particular, the optic body is a crosslinked acrylic material comprising copolymers of methacrylate and acrylate esters which are relatively hard when cold and relatively soft at body temperature, crosslinked with a diacrylate ester to produce a cross-linked acrylic material having a substantially tack-free surface, a crosslink density between 0.5×10−2 and 1.5×10−2 moles per liter, a glass transition temperature in the range of −30° to 25° C., a tensile modulus in the range of 1000 to 3000 psi and an elongation at break of between 100 and 300%. Such a lens body is easily folded, rolled or otherwise deformed into a low profile for insertion through a small incision and after insertion will naturally return to its original optical resolution at a slow controlled rate in between 20 and 180 seconds even if the lens body has been deformed to a low profile condition for an extended period of time. The slow return allows the surgeon adequate time to locate the folded IOL in the eye before the lens body returns to its original shape and resolution and insures that the unfolding of the lens will not damage or otherwise traumatize ocular tissue. Furthermore, the optic body of the foregoing material and composition possesses a desired tensile strength to resist deformation in response to forces exerted by tissue growing around the implanted lens body thereby maintaining the desired optical characteristics and resolution of the lens body.
In some embodiments, in the formation of the deformable-elastic acrylic material, the copolymers of methacrylate and acrylate esters are mixed at approximately a 45 to 55 weight percent ratio and the relatively hard methacrylate ester is a fluoroacrylate. The fluoroacrylate functions as a surface energy lowering agent as well as a monomer providing long term stable inertness and tensile strength to the polymer without adversely effecting the pliancy of the resulting material. In this regard, the fluoroacrylate is present in a concentration range by weight of between 5 and 25% and preferably is trifluoro ethyl methacrylate. Also in the preferred formulation of the crosslinked acrylic, the mixture of the copolymers is partially polymerized prior to chemical crosslinking with diacrylate ester in a concentration range of between 0.5 and 3.0 percent by weight. The polymer may incorporate an ultraviolet (UV) light blocking additive, preferably a permanent (chemically bound) ultraviolet (UV) light-blocking additive known in the art, such as 2-(4-benzoyl-3-hydroxyphenoxy) ethyl acrylate.
The resulting crosslinked acrylic material may be molded and formed into lens bodies machined to have the desired optical characteristics and resolution with haptics extending therefrom either integral with or separately attached to the lens body.
In a preferred embodiment, the optic body 11 is made of SENSAR® IOL brand of hydrophobic acrylic IOL material.
Although the crosslinked acrylic material described herein is described primarily for use in an optic body, the crosslinked acrylic material may be used in other applications wherein a change of refractive index is desired.
The optic body 11 material is preferably selected such that the optical zone 12 is optically clear and exhibits biocompatibility in the environment of the eye. Selection parameters for suitable lens materials are well known to those of skill in the art. See, for example, David J. Apple, et al., Intraocular Lenses. Evolution, Design, Complications, and Pathology, (1989) William & Wilkins. Foldable/deformable materials are particularly advantageous since optics made from such deformable materials may be rolled, folded or otherwise deformed and inserted into the eye through a small incision. The lens material before irradiation preferably has a refractive index allowing a relatively thin, and preferably flexible optic section, for example, having a center thickness in the range of about 150 microns to about 1000 microns, depending on the material and the optical power of the optic body 11. For example, in one embodiment, the optic body 11 is made of SENSAR® IOL brand of acrylic material, an optically clear, hydrophobic, acrylic elastomer with an optical power of 20 D. IOLS made of the composition contained in the SENSAR® IOL brand are described in commonly-owned U.S. Pat. No. 4,834,750, which is incorporated here by reference. In such an exemplary embodiment, the optical zone 12 has a center thickness Tc that is preferably in the range of about 0.5 mm or less to about 1.0 mm or more, more preferably between about 0.7 mm and 0.9 mm. The center thickness Tc may vary from these ranges depending on factors such as the lens material and the dioptric power of the optical zone 12. The optic body 11 preferably has a diameter of at least about 4 mm to about 7 mm or more, more preferably about 5 mm to about 6.5 mm or about 6.0 mm. As used herein the term “thickness” generally refers to a dimension of a portion or feature of the intraocular lens 10 as measured substantially along the optical axis 22.
The intraocular lens 10 may comprise any of the various means available in the art for centering or otherwise locating the optical zone 12 within the eye. For example, as illustrated in
The optical zone 12 may take any of the forms known in the art. For example the optical zone 12 may be biconvex, plano-convex, plano-concave, meniscus, or the like. The optical power of the optical zone 12 may be either positive or negative. The general profile or shape of the posterior face 18 and the central face 24 of the optic zone 12 may be any used for producing an optic based on refraction of incident light. For instance, the posterior face 18, the central face 24, or both faces 18, 24 may be spherical with an overall radius of curvature that is either positive or negative. Alternatively, the profile or shape of either the posterior face 18, the central face 24, or both faces 18, 24 may be parabolic or any aspheric shape common in the art for reducing aberrations such as spherical aberrations. For example, the posterior face 18 or the central face 24 may be an aspheric surface designed to reduce spherical aberrations based on either an individual cornea or group of corneas as described by Piers et al. in U.S. Pat. No. 6,609,673 and U.S. patent application Ser. Nos. 10/119,954, 10/724,852, herein incorporated by reference. Other aspheric and asymmetric surface profiles of the posterior face 18 or the central face 24 of use within the art are also consistent with embodiments of the intraocular lens 10. The posterior face 18 or the central face 24 may alternatively be configured to provide more than one focus, for example to correct for both near and distant vision as described by Portney in U.S. Pat. No. 4,898,461.
The optical zone 12 may take any of the forms known in the art. For example the optical zone 12 may be biconvex, plano-convex, plano-concave, meniscus, or the like. The optical power of the optical zone 12 may be either positive or negative. The general profile or shape of the posterior face 18 and the central face 24 of the optic zone 12 may be any used for producing an optic based on refraction of incident light. For instance, the posterior face 18, the central face 24, or both faces 18, 24 may be spherical with an overall radius of curvature that is either positive or negative. Alternatively, the profile or shape of either the posterior face 18, the central face 24, or both faces 18, 24 may be parabolic or any aspheric shape common in the art for reducing aberrations such as spherical aberrations. For example, the posterior face 18 or the central face 24 may be an aspheric surface designed to reduce spherical aberrations based on either an individual cornea or group of corneas as described by Piers et al. in U.S. Pat. No. 6,609,673 and U.S. patent application Ser. Nos. 10/119,954, 10/724,852, herein incorporated by reference. Other aspheric and asymmetric surface profiles of the posterior face 18 or the central face 24 of use within the art are also consistent with embodiments of the intraocular lens 10. The posterior face 18 or the central face 24 may alternatively be configured to provide more than one focus, for example to correct for both near and distant vision as described by Portney in U.S. Pat. No. 4,898,461.
At least portions of the posterior face 18, the central face 24, or both faces 18, 24 of the optical zone 12 may comprise one or more optical phase plates. In such embodiments, the total optical power of the optical zone 12 is a combination of the refractive power of the posterior face 18 and the central face 24, and the optical power of the one or more diffraction orders produced by the one or more phase plates. The one or more phase plates may be either a monofocal phase plate providing one dominant diffraction order or a multifocal phase plate, such as a bifocal phase plate, for providing, for instance, simultaneous near and distant vision. Other types of phase plates may also be used. For example, the phase plate may be based on a change in the refractive index of the material used to form the optical zone 12.
The total optical power of the optical zone 12 is preferably within a range of at least about +2 Diopters to about +50 Diopters or more, more preferably within a range of about +5 Diopters to about +40 Diopters, and most preferably a range of about +5 Diopters to about +30 Diopters. The total optical power may be either positive or negative, for instance within a range of about −15 Diopters or less to about +15 Diopters or more, or within a range of about −10 Diopters to about +10 Diopters. Other ranges of refractive optical power may be preferred, depending on the particular application and type of intraocular lens to be used.
In certain embodiments, the haptics 32 are characterized by a haptic thickness Th that is equal to a distance, as measured along the optical axis 22, between the distal posterior face 34 of the haptic 32 and the substantially opposing anterior face 58. Preferably, the haptic thickness Th is greater than or approximately equal to an optic edge thickness To, as measured along the optical axis 22. The thicknesses Th and To may be selected based on the particular material from which the intraocular lens 10 is made, the amount of rigidity desired, the optical power of the lens 10, and other such factors. In one embodiment, at least one of the haptic thickness The optic edge thickness To, is between at least about 0.4 mm to about 0.5 mm or more.
As a result of the step edge 39, the distal posterior face 34 of each haptics 32 has an anterior offset relative to the proximal posterior face 38. In certain embodiments, the step edge 39 has a thickness H that is much less than the optic edge thickness To. For example, the step edge thickness H is about 0.1 mm and the optic edge thickness To is between about 0.4 mm or less and about 0.5 mm or more. Alternatively, in other embodiments, the step edge thickness H is greater than or approximately equal to the optic edge thickness To. The step edge thickness H may be selected based on various design parameters, including, the particular material from which the intraocular lens 10 is made, the amount of rigidity desired in the haptics 32, and other such factors. Preferably, step edge thickness H is selected sufficiently large so that the integrity of the contact of the edge corner 50 with the posterior capsule of the eye is maintained so as to help avoid PCO.
In certain embodiments, at least a portion of the step edge 39 is a straight line and is substantially disposed at a radius R1 from the optical axis 22. Alternatively or additionally, at least a portion of the step edge 39 may be arcuate in shape. The radius R1 is advantageously greater than the radius Ro of the optic edge 20 so that a proximal portion of the haptic 32 forms a buttress 51 that is preferably thicker than a distal portion 52 of the haptic 32 and the edge thickness To. The buttress 51 of each haptic 32 provides greater haptic rigidity in the vicinity of the peripheral zone 13, resulting in a biasing force that biases the distal portion 52 of the haptic 32 away from the optical zone 12. The biasing force away from the optical zone 12 can favorably act to reduce the tendency of the haptics 32 to stick to the optical zone 12. Such sticking problems have been noted with certain one-piece IOL materials that are both soft and tacky. Another potential benefit of the step edge 39 is that the thickness of the distal portion 52 of each haptic 32 Th may be fabricated to be less than the thickness of the buttress 51, thus reducing the total volume of the intraocular lens 10 and permitting a smaller incision in the eye to be used during surgery. The greater haptic rigidity in the vicinity of the peripheral zone 13 of the optic body 11 also results in a radial force for centering the intraocular lens 10 within the eye and provides an axial force, as explained below herein. The axial force pushes the edge corner 50 that surrounds the posterior face 18 against the posterior capsule of the eye to help prevent PCO. Disposing the step edge 39 at a radius R1 that is greater than Ro provides yet another potential advantage. The greater rigidity provided by the buttress 51 permits the creation of a flex point Wf near the peripheral zone 13 that allows the haptic 32 to flex in a plane perpendicular to the optical axis 22 while maintaining overall rigidity in the vicinity of Wf. As illustrated in
In certain embodiments, the peripheral zone 13 is substantially formed by the peripheral face 28, the optic edge 20, and the peripheral portion of the posterior face 18. As illustrated in
As illustrated in
In many embodiments, the index of refraction of the acrylic material is achieved by irradiation of the acrylic material with a suitable light source. In many embodiments, the light source is a pulsed laser.
The present invention can be implemented by a system 200 that projects or scans an optical beam into a patient's eye 201 containing the optic 10, such as the system shown in
During operation, the light source 220 generates an optical beam 225 whereby reflection means 270 may be tilted to deviate the optical beam 225 and direct beam 225 towards the patient's eye 201 and particularly into the crosslinked acrylic polymer in order to alter the refractive index of said polymeric acrylic. Focusing lens' 250, 260 can be used to focus the optical beam 225 into the patient's eye 201. The positioning and character of optical beam 225 and/or the scan pattern it forms on the eye 201 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
The selected light source is not particularly limited so long as the emitted radiation is capable of modifying the refractive index of the crosslinked acrylic material in the manner desired. In many embodiments, the selected light source is a laser, and more particularly a pulsed laser source.
In many embodiments, the light source is a 320 nm to 800 nm pulsed laser source. In many embodiments, the light source 220 is a 320 nm to 800 nm laser source such as an tunable femtosecond laser system or it may be a Nd:YAG laser source operating at the 2nd harmonic wavelength, 532 nm, or 3rd harmonic wavelength, 355 nm. Other options are frequency double or tripled femtosecond laser sources which emissions fall in this spectral band. One limit of the suitable wavelengths is the transmission of the cornea. The transmission of the cornea at 355 nm is about 85% and starts to strongly drop off at 320 nm (50% transmission) to 300 nm with about 2% transmission whereas the lens absorption is approximately 99%. Also, for older people, light scattering of the cornea is minimal while light scattering of the lens has considerably increased (cataract). Important to the wavelength selection is that the crosslinked acrylic polymer shows multi-photon (two or three photo for example) absorption at the used laser wavelength and the laser wavelength itself is not linearly absorbed by the material.
In operation, the light of the light source is focused and is scanned in the crosslinked acrylic polymer in order to effect a change of the refractive index in a volume of the crosslinked acrylic polymer. 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. The shape of the volume effected by the irradiation with the light source is not particularly limited. For instance, the volume may be lens shaped, biconvex, plano-convex, plano-concave, meniscus, or the like, disc shaped, parabolic or their wave-stepped Fresnel-type combination thereof—or in any other 3-dimensional shape suitable to cause the desired change in refractive property of the intraocular lens.
Where a pulsed laser source is used, the focused pulsed laser source is swept in an array of laser pulses having a predetermined spot size and spot spacing. The array of laser pulses may be repeated in the same pattern a predetermined number of times such that substantially the same locations within the crosslinked acrylic polymer are irradiated a predetermined number of times. These array repeats may be accomplished by sweeping the laser source such that all the predetermined repeats are irradiated at a first laser position before laser source is moved to a second position in the crosslinked acrylic polymer. These repeats can also just be shifted to a slightly different depth in order to affect relative untreated volume but with the same pattern. Single lay depth difference may be in the order of 1 to 200 um more preferred 2 to 15 um. Alternatively, the array repeats may be accomplished by completing a first sweep of the array with the pulsed laser beam and depositing one pulse at each array position and then repeating the array sweep for subsequent repeat. Preferably, the crosslinked acrylic polymer absorbs at least a portion of the laser radiation.
The pulse energy of laser pulses is generally between 0.01 μJ and 50 μJ. In many embodiments, the pulse energy will be between 0.05 μJ and 20 μJ, or more precisely, between 0.1 μJ and 0.7 μJ, or between 0.05 μJ and 1 μJ.
A pulse repetition rate of the laser pulses is generally between 1 kHz and 10 MHz. In many embodiments, the pulse repetition rate is between 100 kHz to 600 kHz, or between 1 KHz to 80 KHz.
Spot sizes of the laser pulses are generally smaller than 20 μm. In many embodiments, the spot size is preferably smaller than 15 μm, typically 0.5 μm to 3 μm. In some embodiments, the spot size is in the range of 10 μm to 15 μm.
When a pulsed laser source is used, a pulse duration of the laser pulses is generally between 0.1 ps and 10 ns. For purposes of this application, femtosecond laser pulses are generally referred to as pulsed durations from 100 fs to 500 fs, and nanosecond laser pulses are defined as laser pulses from 0.5 ns to 10 ns.
A numerical aperture should be selected that preferably provides for the focal spot of the laser beam to be scanned over a scan range of 6 mm to 10 mm in a direction lateral to a Z-axis that is aligned with the laser beam. The NA of the system should be less than 0.6, preferably less than 0.5 and more preferably in a range of 0.01 to 0.4, typically between 0.03 and 0.3. In some specific embodiments, the NA is 0.15. In a femtosecond laser system, the NA is 0.02 to 0.09 with wavelength being 705 nm.
Irradiation with the light beam as described herein results in a change in refractive index of the cross-linked acrylic polymer, thereby causing the predetermined change in the refractive property of the intraocular lens. Applicants have determined that the crosslinked acrylic polymers exhibit both positive and negative changes in the refractive index of the material after irradiation with the laser light source. That is, the crosslinked acrylic materials exhibit a first change in the refractive index that is negative during a first time period after irradiation and a second change in the refractive index that is positive in a second time period after irradiation. The first time period may precede the second time period or may occur after the second time period. That is, in the crosslinked acrylic material, there is both a positive and negative index change after irradiation, and both the negative and positive changes in the index of refraction contribute to the resulting (i.e. final) index of refraction of the irradiated material.
It should be emphasized that different IOL materials respond to laser irradiation differently in terms of the sign and magnitude of the refractive index change or the time course of the change. The behavior of each material may be understood through experimentation. Some specific examples are described below, and it should be noted that the principle and methods described below may be applied to other IOL materials with suitable modifications.
Without being limited by theory, one effect of the laser irradiation 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 positive change in the refractive index. Another effect of the laser irradiation is to cause local heating portion of the crosslinked acrylic polymer irradiated with the laser pulses, which causes or may cause a negative index change in the material. Also, also changes the hydrophobicity, which causes a positive index change. The index change typically is proportional to total energy.
This feature of having both a positive and negative index change is illustrated in
Following completion of the positive and negative index changes, the irradiated volume of the crosslinked acrylic material reaches a final equilibrium state characterized by an index of refraction that is different from the index of refraction of the crosslinked acrylic polymer in its pre-irradiated state and different from the index of refraction of the of the crosslinked acrylic material that has not been irradiated. That is, the change in refractive index relative to the pre-irradiation refractive index (or relative to the index of the refraction of the non-irradiated portion of the lens) in the crosslinked acrylic polymer is proportion to a total energy of the irradiation with the light source at each location. In preferred embodiments, the change in refractive index relative to the pre-irradiation refractive index (or relative to the index of the refraction of the non-irradiated portion of the lens) in the crosslinked acrylic polymer is linearly proportional to a total energy of the irradiation with the light source at each location.
This feature is shown, for instance, in
It should be noted that for some other IOL materials, the change in refractive index at each location due to laser irradiation may change in a non-linear manner with respect to the total energy of the irradiation. The behavior of each IOL material may be understood through experimentation.
U.S. Pat. Nos. 4,834,750 and 7,615,073 and U.S. Patent Publication 2015/0335477 are incorporated herein by reference in their entirety.
Modification of refractive index of the intraocular lens may be achieved by directly altering the chemical bonds of the crosslinked acrylic material of the lens through multi-photon absorption. To directly alter the chemical bonds, photon energy of >5 eV is needed, which requires two- or three-photon absorption in the visible wavelength range. One problem with this approach is that most IOL materials are specifically made to be very resistant to chemical changes, as they are designed and manufacture to be inert and fully cured prior to implantation and should not react to anything once implanted. In the embodiments described below, instead of changing the chemical bonds to alter the chemical structure of the IOL material, a pulsed laser beam is used to locally alter the refractive index of the IOL material by means of localized heating. Further, the wavelength and power density of the pulse laser beam are selected to induce multiphoton absorption of the laser light. In other words, the laser energy is absorbed by the IOL material through multiphoton absorption, and majority of the absorbed energy is released as heat to heat the IOL material locally to alter its refractive index locally.
In some embodiments, the laser light used for refractive index modification is in either the UV/blue spectral range (e.g. 400-450 nm) or the far red/NIR spectral range (e.g. 650-800 nm), and multi-photon absorption allows for photons in these spectral ranges to be absorbed by the IOL material with relatively high absorption rate. These two wavelength ranges are preferred as they are in ranges of low human retinal sensitivity, compared to the green spectral range which has the highest sensitivity. Low spectral sensitivity therefore allows good patient compliance.
The upper panel of
The direct linear absorption in the blue/UV spectral range may also be used. In this range, however, the photochemical effect on the retina may be a concern, and the treatment must meet the retinal safety limit (which is a very low dosage). Additionally, the limited corneal transmission in this spectral range due to increased light scattering in the aged cornea of the target population may also reduce the effectiveness of such an approach.
While one specific example of IOL material is given above, different IOL materials with different single photon UV absorption characteristic may change the usable spectral range due to the specific cut-off wavelengths of their UV/blue absorbance. For yellow dyed IOL materials, this range can significantly shift into the red spectral region or into the near IR range. Further, specific resonant dye absorbers, which have narrow absorption peaks tailored to specific laser wavelengths, may be introduced into the IOL material. If the bandwidth is narrow enough, it may be used even in the visible spectral range as only little energy is absorbed. Dyes which are specifically only sensitive for two-photon absorption may also be used.
The two-photon absorption coefficient of the IOL material may be derived experimentally.
The two-photon absorption coefficient as a function of the pulse energy may be obtained by measuring the transmission rate of the light through the sample as a function of pulse energy, then fitting two constants (threshold and coefficient) to the measured transmission rate data. In one particular example, the equation used for the curve fitting is as follows:
Where Pm is the incident power on the material, w0 is the Gaussian beam waist radius, and:
Where zR is the Rayleigh range, z0 is the beam waist location, z is the location of bottom of material, zm is location of the top of the material, and β is the TPA coefficient which has two fit parameters Pth and Pwidth as given below:
As mentioned earlier, certain chromophores may be added to the IOL material to absorb other laser wavelengths to induce two-photon absorption and the associated heating. For example, a UV-blocking IOL material, containing a UV filter, such as the TECNIS® OptiBlue IOL, which has relatively high absorption for blue light, can be altered with a 780 nm short pulsed laser as it still has significant absorption at 390 nm, while the non-UV-blocking IOL material, such as the SENSAR® IOL is already in the transition zone for this wavelength. It is also possible to use wavelength specific absorbers for 515 nm light which may then allow the use of 1030 nm lasers light which are non-visible for the patients. The TECNIS® OptiBlue IOL is described in commonly-owned U.S. Pat. No. 7,278,737, which is incorporated herein by reference.
One effect of two-photon absorption is the self-limitation of the laser effect on the material at the focus spot. Such self-limitation is caused by the light 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.
This self-limitation effect can prevent plasma formation and the associated damage of the IOL material due to high power density at the intended focus spot. Thus, higher pulse energy may be used without damaging the IOL material. In other words, this effect intrinsically increases the dynamic range of the desired effect without causing optical breakdown in the laser focus and damage of the sample. On the other hand, the variable depth effect, i.e. the change in absorption depth with pulse energy, means that the laser pulse irradiation pattern should be designed to take this effect into account, so that the actual absorption depth occurs at intended depths. In practice (see
In addition to a Gaussian beam profile, other beam profiles may be used, such as a top hat shaped beam (where the light intensity profile is flat in a center region), a vortex beam (where the light intensity peaks at radial positions away from the beam center), etc. For example, spatial pulse shaping using vortex beams can be utilized to optimize the induced laser efficacy while increasing the threshold for material damage as the threshold for plasma formation is hard to reach under these conditions. A vortex beam can form a ring shaped focus spot in the material, which can result in a more spatially even distribution of energy as compared to a beam profile that peaks at the beam center.
Another factor that generates a self-limiting effect during laser processing of the IOL material is thermal lensing. Thermal lensing in an optical medium is induced by temperature gradient in the medium, which changes the refractive index of the material and causes bending of the light. The effect is temporary, and disappears when the temperature gradient disappears due to heat diffusion. When processing the IOL material using a laser beam, when the pulse repetition rate is sufficiently high and the focus spots of successive pulses are located sufficiently close to each other in space, the focusing of the subsequent pulses may be affected by the thermal lensing effect due to the heat generated by previous laser pulses. The induced thermal lensing may limit the formation of a good laser focus spot, i.e., it may defocus the laser beam.
The magnitude of the thermal lensing effect for a given material may be estimated by numerical simulation. In methods described below that take thermal lensing effect into consideration, simulation results may be used to determine, for a given set of parameters, whether the effect of thermal lensing is desirable/undesirable or acceptable/unacceptable, or to optimize various parameters, depending on practical requirements.
Generally speaking, if defocusing of the laser beam is to be avoided, the successive laser spots in a scan pattern should be placed outside of the thermal impact zone of the previous pulses. On the other hand, the defocusing reduces the energy density at the focus spot, which may beneficially avoid plasma formation at the focus spot and the resulting damage of the lens material. As a result of the defocusing, a much higher average power of the laser beam may be used without causing plasma formation and damage to the IOL material. Thus, in some embodiments, the laser parameters (such as pulse energy, pulse repetition rate, etc.) and the scan pattern (such as the spot spacing between adjacent laser spots) are designed such that a thermal lensing effect is induced in the IOL material to cause subsequent laser pulses to be defocused. When such a technique is used, a laser beam of higher average power may be used without damaging the IOL material.
Another method that takes thermal lensing effect into consideration is interlaced scan patterns. The thermal lensing effect is such that placing one pulse or line too close to a previous one may reduce the efficiency of the index change. By creating a pattern that increases the time given for heat to dissipate before the laser returns, efficiency can be increases. For example, if multiple laser scan layers 1, 2, 3, 4, 5, 6, 7, and 8 are to be formed in that spatial order (e.g. from deep to shallow, or from shallow to deep), then instead of forming the layers in a time order of layers 1, 2, 3, 4, 5, 6, 7, and 8, the layers may be formed in an interlaced time order such as layers 1, 3, 5, 7, 2, 4, 6, and 8; or 1, 5, 2, 6, 3, 7, 4, and 8; or some other interlaced scheme. Similarly, for the scan lines within a scan layer or the spots within a scan line, the lines or spots may be formed in the interlaced manner. More generally, an interlaced pattern here refers to a laser pulse scan pattern where layers (or lines, or spots) that are immediately adjacent each other in the spatial order are not immediately adjacent each other in the time order. Numerical simulations mentioned earlier may be used to determine what spatial spacing is needed for a given laser pulse repetition rate to avoid unacceptable thermal lensing, so as to design the interlaced scan pattern accordingly. By generating interlaced scan patterns, one can generate significant index changes with high efficiency without damaging the lens material.
In another scanning method that utilizes the thermal lensing effect, pre-pulses that have much lower energy than the refractive index modifying pulses (e.g., 1:10 to 1:100 of the energy of the refractive index modifying pulses) are delivered to the IOL material at suitable locations to heat the IOL materials to form a transient thermal lens, which will slightly defocus the subsequent refractive index modifying pulses that immediately follow the pre-pulses. The delay between pre-pulse and pulse should be about 100 ps to 100 ns. One practical benefit of this technique is to deal with the fact that the patient's corneal transparency may deviate spot to spot significantly. At places where the corneal transparency is high, the pulse energy that reaches the IOL material will be stronger; at these places, thermal lensing effect in the IOL will also be stronger, causing the laser focus spot to be more defocused, thereby reducing the power density at the focus spot. Thus, the thermal lensing effect can mitigate the undesirable effect of variation in the patient's corneal transparency. Another practical benefit of thermal lensing is that it allows for the use of optical systems with relatively low numerical aperture. In-vivo refractive index modification requires relatively low (<0.2) numerical aperture (NA). Small NA is beneficial for cost of the system and efficacy of the refractive index modification. NA less than 0.01 can become dangerous, however, because of the small beam diameter on the retina. Using the pre-pulsing technique, or simply taking advantage of the previous treatment pulses, to create thermal lens on the way to the retina, the beam can be defocused, and the light spot on the retina is correspondingly larger.
In practice (see
To obtain high refractive index differences within an IOL material, multiple modified layers may be spatially stacked on top of each other, and the refractive index changes of the multiple modified layers add to each other along the optical path in a generally linear relationship. Similar effects can be generated by use of a laser optical system with a relatively low NA, which forms a longer (in the depth direction) focus spot that can generate the full desired refractive index change of the IOL within one modified layer.
To produce desired refractive index change over a volume of the lens, refractive index change produced by single laser pulses are combined by scanning the pulsed laser beam (“writing”) according to a pattern. Scanning a pattern of laser pulses in the lens loads the lens with thermal energy, as significant amount of energy is absorbed in the IOL as described earlier. The thermal load in the lens need to be carefully managed. Numerical simulation, such as thermal FEM modeling, may be used to calculate expected temperature distribution produced by a pulsed laser scan pattern.
For safe human applications, the optical geometry of the laser system may be designed to ensure a sufficiently large light distribution area on the retina in order to reduce light intensity there. Because the laser beam is focused inside the IOL and then passes through the IOL to reach the retina, and because the IOL has a positive optical power, the refractive power of the IOL will cause the beam spot on the retina to be more concentrated as compared to when the IOL is not present. To ensure that safety limits for the retina are satisfied, the beam concentration effect of the IOL may be counteract by pre-compensating the input laser beam. In one embodiment, the pre-compensation is achieved by directing the laser beam to the IOL at an angled direction that is non-parallel to the optical axis. As a result, higher laser power may be used to process the IOL without exceeding the safety limit for the retina, which improves the laser processing speed. This is illustrated in
The heat induced refractive index change in IOL materials may be positive or negative, depending on the laser energy and other parameters, and may change with time after laser irradiation. After a certain time, such as one day, the change of refractive index will stabilize. Different IOL materials also respond differently to the laser treatment. For example, the final index change is mostly positive for the SENSAR® IOL material, but may be negative for some other IOL materials, such as for example, acrylic IOL materials having a higher water content. The amount of induced refractive index change may be measured for each IOL material, for example, using a phase shifting interferometer.
In practice, for a given IOL material, the amount of induced refractive index change, as a function of laser energy and other parameters such as NA, laser pulse duration, laser repetition rate and pattern (such as spot spacing and timing, due to thermal lensing), laser wavelength, etc., is empirically determined. Based on such data, the laser parameters and scan pattern can be designed to achieve a given target result of desired refractive index modification of the IOL. More specifically, as shown in
In an alternative embodiment, by scanning the pulsed laser beam in the IOL in concentric patterns, concentric rings of refractive index variation may be generated, forming a Fresnel lens. Such a lens may provide high optical power changes (it adds an optical power to the optical power of the IOL), as high as multiple diopters. In one example, a Fresnel lens formed this way (see
As discussed above, the change in refractive index of the IOL in response to laser treatment depends on a multitude of factors, and at the same time, the laser treatment is limited by various eye safety concerns. Therefore, suitable laser system parameters for a refractive index modification procedure may vary greatly. In some embodiments, for the SENSAR® IOL material, the various laser system parameters fall within the following preferred ranges. Laser wavelength: 650 to 800 nm, more preferably, 680 to 720 nm; laser pulse energy: 10 nJ to 10 uJ, more preferably, 100 nJ to 2 uJ; laser pulse duration: 10 fs to 10 ps, more preferably, 100 to 600 fs; laser pulse repetition rate: 10 to 1000 kHz, more preferably, about 300 kHz; laser focus spot size: 5 to 25 um, more preferably, 7 to 12 um; numerical aperture (NA) of the incident beam: 0.01 to 0.15, more preferably, 0.03 to 0.12; number of repeats (successive laser pulses irradiated at the same position): 1 to 14. For the laser scan pattern, the spot spacing in the transverse direction will typically change with focus spot size and repetition rate; the spot spacing should be sufficiently small to create substantially uniform index change zone throughout. For a beam with a Gaussian profile, the spot spacing is preferably smaller than the beam spot size. The spot spacing may be different in different scan directions of the scan pattern. In the depth direction, the spot separation is 1 to 100 um, and more preferably, 3 to 10 um.
In one particular example that used a circular scan pattern, the spot spacing was 2.5 um in the angular direction and 4 um in the radial direction (i.e. between adjacent circles of the scan pattern), and the beam had a super-Gaussian profile with an 8 um diameter. In this example, the pulse energy was 0.9 uJ, a total of 10.8 J of energy was deposited in a 20 mm2 area, and the treatment time 0.1 W power was 108 seconds. The phase change generated by one layer of modification was about 0.06λ, and about 1.2λ for 20 layers.
In summary, the use of multi-photon absorption allows for the use of high absorption of the IOL material in the UV/blue spectral and in the far red spectral range, where the photopic sensitivity of the eye is relatively low. The use of laser wavelengths outside the spectral sensitivity of the human eye allows treatment of patients without the significant visual effects during patient exposure and good patient compliance during the laser treatment. Due to the short pulse duration needed to get a two photon absorption, effective heating shorter than the thermal relaxation time is enabled. Additionally, due to the non-linear absorption of two or more photons, the exposure in the laser focal volume is self-limiting as the laser light upfront of the laser focus will start to be absorbed as soon as the threshold of multiphoton absorption is reached. Further, the effect of thermal lensing, i.e. the defocusing of subsequent neighboring laser spots in the scan pattern due to thermal lensing caused by the previous laser pulses, may be avoided by placing subsequent laser pulse spots outside of the thermal impact zone of the previous pulses; the thermal lensing effect may also be taken advantage of to defocus the laser spots which allows for higher pulse energy to be used. Also, the overall thermal management of the induced thermal load within the IOL and surrounding tissue becomes and important practical consideration, as overloading the IOL and surrounding tissue with heat should be avoided to avoid thermal damage.
The refractive index modification methods described above may also be used for customization of IOLs during production, or in-office modification after production but before implantation into patients' eyes. In such applications, the wavelength restrictions and the eye safety considerations are eliminated because no patient's sys is present, and higher laser power may be used to increase the processing speed. In an in-office modification process, the target refractive index modification is customized for the intended patient, and the laser scan patterns is designed to achieve such a target modification.
In addition to IOLs, the refractive index modification methods described above may also be used to modify the refractive properties of contact lenses.
In various embodiments described above, the methods for modifying refractive index of the IOL material may be carried out by the laser system describe earlier which includes the control electronics 210. The control electronics 210 may include a computer, microcontroller, etc., and associated memory devices that store computer readable program code. The computer or microcontroller executes the computer readable program code to control the laser light source 200 and other components of the laser system 200 to execute the above described methods.
The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. The term “connected” is to be construed as partly or wholly contained within, attached to, or joined together, even if there is something intervening. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate embodiments of the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.
While certain illustrated embodiments of this disclosure have been shown and described in an exemplary form with a certain degree of particularity, those skilled in the art will understand that the embodiments are provided by way of example only, and that various variations can be made without departing from the spirit or scope of the invention. Thus, it is intended that this disclosure cover all modifications, alternative constructions, changes, substitutions, variations, as well as the combinations and arrangements of parts, structures, and steps that come within the spirit and scope of the invention as generally expressed by the following claims and their equivalents.
This application claims priority to and is a continuation of U.S. patent application Ser. No. 16/375,784, filed Apr. 4, 2019, now U.S. Pat. No. 11,154,424, which claims the benefit under 35 U.S.C. § 119(e) of U.S. Provisional Patent Application Nos. 62/654,192, filed Apr. 6, 2018 and 62/720,882, filed Aug. 21, 2018. The contents of the above applications are incorporated herein by reference in their entireties.
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| Child | 17451812 | US |
