Patent Application
20060264917
Embodiments of the present invention are generally related to vision correction systems. In one embodiment, the invention provides systems and methods for verifying a laser refractive procedure, ideally by ablating a customized corrective scleral contact lens before imposing a corresponding refractive correction in the corneal tissues.
Known laser eye procedures generally employ an ultraviolet or infrared laser to remove a microscopic layer of stromal tissue from the cornea of the eye to alter the refractive characteristics of the eye. The laser removes a selected shape of the corneal tissue, often to correct refractive errors of the eye. Ultraviolet laser ablation results in photodecomposition of the corneal tissue, but generally does not cause thermal damage to adjacent and underlying tissues of the eye. The irradiated molecules are broken into smaller volatile fragments photochemically, directly breaking the intermolecular bonds.
Laser ablation procedures can remove the targeted stroma of the cornea to change the cornea's contour for varying purposes, such as for correcting myopia, hyperopia, astigmatism, and the like. Control over the distribution of ablation energy across the cornea may be provided by a variety of systems and methods, including the use of ablatable masks, fixed and moveable apertures, controlled scanning systems, eye movement tracking mechanisms, and the like. In known systems, the laser beam often comprises a series of discrete pulses of laser light energy, with the total shape and amount of tissue removed being determined by the shape, size, location, and/or number of a pattern of laser energy pulses impinging on the cornea. A variety of algorithms may be used to calculate the pattern of laser pulses used to reshape the cornea so as to correct a refractive error of the eye. Known systems make use of a variety of forms of lasers and/or laser energy to effect the correction, including infrared lasers, ultraviolet lasers, femtosecond lasers, wavelength multiplied solid-state lasers, and the like. Alternative vision correction techniques make use of radial incisions in the cornea, intraocular lenses, removable corneal support structures, thermal shaping, and the like.
Known corneal correction treatment methods have generally been successful in correcting standard vision errors, such as myopia, hyperopia, astigmatism and the like. However, as with all successes, still further improvements would be desirable. Toward that end, wavefront measurement systems are now available to measure the refractive characteristics of a particular patient's eye. By customizing an ablation pattern based on wavefront measurements, it may be possible to correct minor regular and/or irregular refractive errors so as to reliably and repeatably provide visual acuities of 20/20 or better. Unfortunately, these measurement systems are not immune from measurement error. Similarly, the calculation of the ablation profile, the transfer of information from the measurement system to the ablation system, and the operation of the ablation system all provide opportunities for the introduction of errors, so that the actual long term visual acuities provided by real-world wavefront-based correction systems may not be as good as might be theoretically possible.
In light of the above, it would be desirable to provide improved vision correction systems and methods.
Various embodiments of the invention provide methods and systems for verifying procedures used to correct aberrations in the eye resulting in vision defects such as myopia, etc. Particular embodiments are useful for pre-operatively verifying the effectiveness of laser eye surgical procedures such as photorefractive keratectomy (PRK), phototherapeutic keratectomy (PTK), laser in situ keratomileusis (LASIK), and the like.
In a first aspect, the invention provides a method for verifying vision correction for an eye of a patient. The method comprises measuring irregular aberrations of the eye. A determination is made for a proposed refractive correction for treatment of the eye. The determination can be based on the measured aberrations or other optical evaluation of the eye. A central portion of a verification lens is configured to correspond with the proposed correction. A peripheral portion of the verification lens is positioned upon the sclera of the eye so that the central portion is optically aligned with the aberrations. This can be accomplished by registering the verification lens with the eye. Then a determination is made whether the corrected vision of the eye with the verification lens is acceptable. This determination is used to verify the proposed correction. The determination can include an evaluation of one or more of visual acuity, accommodation and contrast sensitivity as well the reading of an eye chart. The determination can be made after the verification lens has been worn for a period of hours, a day or even multiple days. Also, several determinations can be made over a desired period and the results compared (e.g., by quantitative or qualitative means). Various embodiments of the method can be used to evaluate a number of eye treatments including laser refractive treatments and the like. Also, in many embodiments, the irregular aberrations or other optical errors of a patient's eye can be measured with a wavefront sensor which, in specific embodiments, can be configured to measure refractive error. Measurements from the wavefront sensor can be used to produce a wavefront shape which can be used to configure the verification lens to correspond to the proposed correction. For example, in one embodiment, the wavefront shape is used to generate an ablation pattern (described below) for fabrication of the verification contact lens or a corrective contact lens worn by the patient on a long term basis.
In various embodiments, a treatment portion of the lens can have an aspheric shape configured to correspond to a proposed correction to treat various conditions of the eye such as refractive errors, higher order aberrations and presbyopia. Typically, the treatment portion comprises a central portion of the lens, but can comprise a non-central portion or even the entire lens.
In various embodiments, the peripheral portion of the lens can be configured to stabilize or otherwise reduce movement of the verification lens. For example, in one embodiment, the peripheral portion is used to stabilize the verification lens during determination of the corrected vision. This can be accomplished by configuring the peripheral portion to have a surface contour corresponding to a surface contour of the sclera so that the peripheral contour stabilizes the verification lens on the eye. The peripheral portion can also be used to reduce movement of the verification lens such as that which may result from blinking, eye movement (e.g., nystagmus) or head movement or a combination thereof. Also, the peripheral portion can be used to facilitate registration by supporting a substantial portion of the verification lens on the eye.
In various embodiments, the verification pattern can be an ablation pattern. The ablation pattern can be generated based on a proposed refractive correction treatment of the eye. The ablation pattern for the verification lens can be calculated from the measured irregular aberration of the eye, and from characteristics of the lens material, such as a refractive index of the lens material, a rate of ablation of the lens material, and/or ablation properties of the lens material (e.g., the propensity of the lens material to differ in ablation depth across a uniform ablation energy beam, such as any “central island” properties of the lens material). A corneal tissue of the eye may also be ablated according to an ablation pattern, and the ablation pattern may similarly be calculated based on the measured optical error of the eye and on the corneal tissue characteristics, such as a refractive index of the corneal tissue, a rate of ablation of the corneal tissue, and/or a shape of ablation of the corneal tissue. In many embodiments, the wavefront shape can be used to generate the ablation pattern to produce a corrective scleral lens which can be worn by the patient on a long term basis similar to conventional correct contacts lenses known in the art. (e.g., daily wear, extended wear, etc.)
In another aspect, the invention provides a method for forming a lens used to verify vision correction treatment for an eye of a patient or a corrective lens configured to be worn by the patient on a long term basis. The method includes measuring irregular aberrations of the eye and then determining a proposed refractive correction for treatment of the eye. An ablation pattern is then calculated based on the refraction correction, wherein the lens ablation pattern corresponds to an intended eye ablation pattern. A lens work piece is provided which has a central portion and a peripheral portion. The peripheral portion is configured to be positioned on the sclera of the eye. The lens workpiece is then ablated using an ablation system such that the ablation pattern is imposed on the central portion. In an exemplary method, the ablation system can be a laser ablation system but other lens shaping equipment and processes such as lathing or milling are equally applicable. Optionally, the lens workpiece can be a plano lens.
In still another aspect, the invention provides a system for correcting and/or verifying correction of irregular aberrations of an eye of a patient. The system includes a sensor for measuring the irregular aberrations of the eye and a processor for generating a verification pattern of laser energy corresponding to a refractive procedure plan of the eye. The procedure plan is intended to correct the measured irregular aberrations. The verification pattern can be an ablation pattern corresponding to an intended ablation pattern for treatment of the eye according to the procedure plan. The system also includes a lens workpiece and a laser system for directing laser energy onto the lens workpiece according to the verification pattern such that optical properties of the eye, as corrected by the verification lens, can verify the procedure plan. The workpiece has a central portion and a peripheral portion with the peripheral portion being configured to be positioned on the sclera. In various embodiments, the peripheral portion can be configured to optically align the central portion with aberrations on the eye, support a substantial portion of lens on the eye as well as stabilize the lens on the eye.
In other aspects, the invention also provides related systems for verifying and/or correcting various optical errors of an eye.
FIGS. 4A-C illustrate materials and lens assemblies that can be used to fabricate a verification contact lens,
Embodiments of the present invention are particularly useful for enhancing the accuracy and efficacy of laser eye surgical procedures such as photorefractive keratectomy (PRK), phototherapeutic keratectomy (PTK), laser in situ keratomileusis (LASIK), and the like. Preferably, embodiments of the invention can provide verification of the improvement of the optical system in the eye and provide feedback to physicians before the vision correction procedures. All references referred to in this application are hereby incorporated herein by reference.
The system of the present invention can be easily adapted for use with existing laser systems. By providing verification of actual improvements of the optical system in the eye, embodiments of the invention also allow the physician to evaluate the procedure plan, and whether additional measurements or an alternative plan should be prepared. Thus, the feedback provided by embodiments of the invention may facilitate sculpting of the cornea so that the eye meets and/or exceeds the normal 20/20 threshold of desired vision. In various embodiments, additional vision criteria may used either alone or in combination with an evaluation of acuity. For example, an embodiment of the invention provides patient feedback on near acuity and/or long-term effects, optionally providing near acuity of J3 or better and in some cases J1 or better.
Referring now to
In various embodiments laser 12 comprises an excimer laser, which in a preferred embodiment comprises an argon-fluorine laser configured to produce pulses of laser light having a wavelength of approximately 193 nm. Laser 12 will preferably be designed to provide a feedback stabilized fluence at the patient's eye, delivered via delivery optics 16. Embodiments of the invention may also be useful with alternative sources of ultraviolet or infrared radiation, particularly those adapted to controllably ablate the corneal tissue without causing significant damage to adjacent and/or underlying tissues of the eye. Such sources include, but are not limited to, solid state lasers and other devices which can generate energy in the ultraviolet wavelength between about 185 and 215 nm and/or those which utilize frequency-multiplying techniques. Hence, although an excimer laser is the illustrative source of an ablating beam, other lasers may be used in the present invention. Also, in other embodiments, system 10 need not be a laser based system but can be any optical or other lens profiling system known in the art for producing a verification lens such as a scleral contact lens.
Laser 12 and delivery optics 16 will generally direct laser beam 14 to the eye of patient P under the direction of a computer or processor 22. Processor 22 will generally selectively adjust laser beam 14 to expose portions of the cornea to the pulses of laser energy so as to effect a predetermined sculpting of the cornea and alter the refractive characteristics of the eye. In many embodiments, both laser 14 and the laser delivery optical system 16 will be under computer control of processor 22 to effect the desired laser sculpting process, with the processor ideally altering the ablation procedure in response to inputs from the optical feedback system described herein below. The feedback will preferably be input into processor 22 from an automated image analysis system, or may be manually input into the processor by a system operator using an input device in response to a visual inspection of analysis images provided by the optical feedback system. Processor 22 will often continue and/or terminate a sculpting treatment in response to the feedback, and may optionally also modify the planned sculpting based at least in part on the feedback.
Laser beam 14 may be adjusted to produce the desired sculpting using a variety of alternative mechanisms. The laser beam 14 may be selectively limited using one or more variable apertures. An exemplary variable aperture system having a variable iris and a variable width slit is described in U.S. Pat. No. 5,713,892, the full disclosure of which is incorporated herein by reference. The laser beam may also be tailored by varying the size and offset of the laser spot from an axis of the eye, as described in U.S. Pat. Nos. 5,683,379 and 6,203,539 and 6,331,177 the full disclosures of which are incorporated herein by reference.
Still further alternatives are possible, including scanning of the laser beam over the surface of the eye and controlling the number of pulses and/or dwell time at each location, as described, for example, by U.S. Pat. No. 4,665,913 (the full disclosure of which is incorporated herein by reference) and as demonstrated by other scanning laser systems such as those manufactured by LaserSight, Alcon/Summit/Autonomous, WaveLight Technologies AG, Chiron Technolas, and by Bausch and Lomb. Other approaches can include using masks in the optical path of laser beam 14 to vary the profile of the beam incident on the cornea and using hybrid profile-scanning systems in which a variable size beam (typically controlled by a variable width slit and/or variable diameter iris diaphragm) is scanned across the cornea as described in U.S. Pat. No. 6,673,062, the full disclosure of which is incorporated herein by reference. The computer programs and control methodology for these laser pattern tailoring techniques are well described in the patent literature.
Referring now to
Based on the measurements of the eye, a corneal ablation pattern may be calculated 44 by processor 22 (or by a separate processor) for ablating the eye with system 10 so as to correct the optical errors of the eye. Such calculations will often be based on both the measured optical properties of the eye and on the characteristics of the corneal tissue targeted for ablation (e.g., the ablation rate, the refractive index, the propensity of the tissue to form “central islands” or decreased central ablation depths within a uniform energy beam, and the like). The results of the calculation will often comprise an ablation pattern in the form of an ablation table listing ablation locations, numbers of pulses, ablation sizes, and or ablation shapes to effect the desired refractive correction. The ablation table in turn can be stored in an electronic database known in the art (e.g., a relational database) and/or in memory resources known in the art (e.g., RAM, ROM, etc.). An exemplary method for generating ablation patterns is described in U.S. Pat. No. 6,673,062, the full disclosure of which is incorporated herein by reference.
Rather than directly proceeding to the ablation, another ablation pattern may also be calculated 46 for ablation of a verification lens 90. In an embodiment, verification lens 90 can be a scleral contact lens 90s having a peripheral portion 90pp and a central portion 90cp as is described herein. The ablation pattern for the verification lens may be calculated based on the measured optical properties of the eye, together with the characteristics of a lens material including the refractive index of the lens material, the ablation rate of the lens material, any ablation shape-effects of the lens material, and/or the like. The verification lens may then be aligned with the ablation system and ablated 48 using system 10 or optionally, using a system similar to that shown in U.S. Pat. No. 6,638,271 which is also incorporated herein by reference. However, other contact lens laser ablation systems known in the art may also be used. For embodiments using a scleral lens, the ablation pattern is imposed on the central portion of the lens so that the resulting optical profile of the central portion corresponds with the proposed ablative (or other) correction of the eye.
After the verification lens has been generated, the lens is positioned on the patient's eye and evaluated for proper fit and/or alignment 50. Alignment step 50 can be accomplished using visual observation and/or other contact lens fitting methods known in the art. In one embodiment, the doctor can verify that the central portion 90cp is aligned with the cornea C using topographic measurement system 100 or other eye measurement means known in the art. System 100 can also be used to verify that the curvature of lens profile 90p matches that of corneal profile Cp. In embodiments where lens 90s has alignment indicia 92a (described herein), alignment step 50 can be facilitated by a visual determination to make sure that the alignment indicia 92a align with iris patterns IP, the Limbus Li or other feature of the eye. If the lens is not properly aligned, the physician can perform an in situ alignment manually or with the aid of a corneal keratometer or topographic measurement system 100 or other corneal/contact lens instrument known in the art. Proper alignment provides a higher correlation between the corrective effect produced by the verification lens and the corrective effect of the intend eye ablation procedure.
In various embodiments, a pre-alignment step 41, may be done prior to wavefront measurements. Similar to alignment step 50, pre-alignment can be accomplished using visual observation and/or other contact lens fitting methods known in the art. Pre-alignment may be particularly useful where the wavefront is subsequently measured with the scleral lens in place, using registration marks (described herein) indicating how the scleral lens rests on the cornea. Embodiments having pre-alignment provide a means for improving the correlation between the correction produced by the verification lens and the subsequent ablation procedure. In alternative embodiments, a combined wavefront-topography system can be used to make measurements which account for aberrations of the eye as well as the surface contour of the eye for fitting the lens.
After an alignment/fitting determination, visual performance using the verification lens can be assessed 52. Visual performance assessment 52 can be done immediately after the fitting determination, that same day after the patient has worn the lens for a number of hours or even after the patient has worn the lens for a number of days (e.g., two or more) though not necessarily continuously. The types of visual determination which can be made include without limitation, measurement of visual acuity (e.g., using a standard eye chart), depth of field, accommodation, contrast sensitivity and combinations thereof. One or more of these tests may be done under varying lighting conditions. The patient could also complete a subjective visual performance questionnaire. Information from one or more of these tests could be stored on a database and be used for evaluation of subsequent visual corrective plans for the particular patient, or a patient population or even a sub-population (e.g., pediatric patients or myopic patients). When using a scleral verification lens 90s, prior to the visual assessment, the patient may register the verification lens with their eye by positioning the peripheral portion of the lens on the sclera so that the central portion of the lens is optically aligned with aberrations of the eye.
Visual performance of the verification lens may be assessed by having the patient scan an eye chart to determine visual acuity. If the measured visual acuity is equal to or better than some predetermined threshold value, often 20/20 or better and optionally 20/15 or better, the eye is ablated with the planned ablation pattern 54. If not, a second measurement may be taken and the process repeated, and if acuity still remains unacceptable, the ablation may not be performed 56.
Referring now to FIGS. 3A-E, a discussion will now be presented of verification lens 90. Current contact lenses include corneal lenses and scleral lenses. For purposes of this disclosure, verification lens 90 is a scleral lens 90s. As shown in
A scleral contact lens may overcome the stability limitations of a corneal lens. As shown in
In many embodiments, the scleral contact 90s can not only be configured as a verification lens, but also as a corrective lens 90sc which can be worn by the patient to correct their vision as other corrective contact lens are used (e.g., hard and soft contact lens, etc). In various embodiments, lens 90sc can be configured as a daily wear lens, or an extended wear lens. In preferred embodiments, lens 90sc is fabricated using wavefront-driven measurements of aberrations of the eye, including measurements of irregular aberrations, as is described herein. Such methods can also incorporate measurement of the topography of the eye using, e.g., a corneal topographic measurement system described herein. These measurements can be done before or after wavefront measurements. After the corrective lens is fabricated, the wavefront measurement can also be repeated with the corrective lens in place on the eye, to verify the correction of the lens. The information from wavefront measurements with the lens in the eye, can also be used to titrate or fine tune the corrective profile of the corrective lens using lens fabrication methods described herein (e.g., lens ablation methods). Corrective lens 90sc can be a soft or hard contact lens and can thus be fabricated using soft or hard contact lens materials and processing methods known in the art including gas permeable materials and technology. Also, as is described below, corrective lens 90sc can be configured to have an aspheric shape to correct for standard errors, such as refractive errors, as well as irregular errors such as higher order aberrations and presbyopia.
In various embodiments, the scleral lens can be configured to have an aspheric shape or contour 90ac as is shown in
The peripheral portion 90pp of the lens can extend radially from over the outer portions of the cornea then extend over the limbus Li and then over selectable portions of the sclera S. Alternatively, the central portion 90cp can extend over the entire cornea C (even into the limbus Li), with the peripheral portion 90pp beginning in the limbus Li. In many embodiments, the peripheral portion can extend sufficiently over the sclera such that it underlies the eye lid even when the eye is open. This provides one means for stabilizing lens 90s on the eye and reducing movement of the lens from blinking, head movement etc. Other means are discussed below.
The peripheral portion 90pp can be configured to stabilize lens 90s on the eye so as to reduce lens movement from blinking, eye movement, head movement and other biomechanical movements. In an embodiment shown in
A discussion will now be presented of fabrication methods for a scleral lens. In various embodiments, lens 90s can be fabricated using laser ablation methods described herein or known in the art as well conventional contact lens fabrication methods. Referring now to
Suitable lens materials for lens blank 89 can include a variety of contact lens materials including a PMMA (polymethylmethacrylate) fluorocarbon copolymer, silicon acrylate and combinations thereof or other gas permeable lens materials known in the art. Also, the lens material can be selected to produce a rigid or flexible lens as well as a gas permeable lens and can thus include any number of gas permeable polymers known in the art. In a preferred embodiment, the lens material is a gas permeable lens material.
All or a portion of the ablation process can be controlled using processor 22 or other electronic control means known in the art. Accordingly processor 22 can be configured to calculate, modify or store the desired ablation pattern. Also processor 22 can be configured to control the generation of the alignment indicia 92a. In one embodiment, a stream of inert gas such as nitrogen can be blown over the lens before, during or after ablation. Other suitable gases include argon and helium. The flow of the gas can be controlled by processor 22 to increase or decrease the flow rate and/or velocity as needed. In various embodiments, processor 22 or other control means can be used to control one or more gas flow parameters responsive to one or more of the temperature of blank 89/lens 90s, rate of ablation, optical fluence, laser intensity, laser power level and the like. In various embodiments, ablation of the verification lens 90 can be performed in a vacuum or pressure chamber not shown.
Referring now to
Referring now to
As shown in
In various embodiments, lens blank 89 or the scleral lens 90s may have pre-registration marks or features 92p that will facilitate alignment of the lens on the eye. As shown in
Referring now to
As shown in
The foregoing description of various embodiments of the invention has been presented for purposes of illustration and description. It is not intended to limit the invention to the precise forms disclosed. Many modifications, variations and refinements will be apparent to practitioners skilled in the art. Further, elements or acts from one embodiment can be readily recombined with one or more elements or acts from other embodiments. Also, elements or acts from one embodiment can be readily substituted with elements or acts of another embodiment. Hence, the scope of the present invention is not limited to the specifics of the exemplary embodiment, but is instead limited solely by the appended claims.
