Method and Systems for Laser Treatment of Presbyopia Using Offset Imaging
An ophthalmic surgery system and method for treating presbyopia by performing ablative photodecomposition of the corneal surface. The offset image of a variable aperture, such as a variable width slit and variable diameter iris diaphragm, is scanned in a preselected pattern to perform ablative sculpting of predetermined portions of a corneal surface. The scanning is performed to ablate an optical zone sized to match the patient pupil with a peripheral transition zone outside the pupil. The shape of the ablated optical zone is different from the shape of the final optical correction on the anterior surface of the cornea. The optical zone corrects for near-vision centrally and far-vision peripherally. A movable image displacement mechanism enables radial displacement and angular rotation of the profiled beam exiting from the variable aperture. The invention enables wide area treatment with a laser having a narrower beam than the treatment area, and can be used in the treatment of many conditions in conjunction with presbyopia such as hyperopia, hyperopic astigmatism and irregular refractive aberrations.
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The present application is a continuation of U.S. Ser. No. 12/436,736 filed May 6, 2009, which is a continuation of U.S. Ser. No. 10/600,027 filed Jun. 19, 2003 (Abandoned), which is a continuation of U.S. Ser. No. 09/901,964 filed Jul. 9, 2001 (now U.S. Pat. No. 6,663,619), which is a division of U.S. Ser. No. 09/261,768 filed Mar. 3, 1999 (now U.S. Pat. No. 6,280,435), which claims the benefit of U.S. 60/076,786 filed Mar. 4, 1998. The full disclosures, each of which are incorporated herein by reference in their entirety for all purposes.BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to surgical modifications to the eye. In a specific embodiment, the invention provides ophthalmic surgery techniques which employ a laser to effect ablative photodecomposition of corneal tissue to correct presbyopia and/or other vision defects.
With aging, a condition of the eye known as presbyopia develops. With this condition, the crystalline lens of the eye loses the ability to focus on near objects when the eye is corrected for far-vision.
Presbyopia is often treated with bifocal eyeglasses. With bifocals, one portion of the lens is corrected for far-vision, and another portion of the lens is corrected for near-vision. By looking down through the bifocals, the user looks through the portion of the lens corrected for near-vision. When viewing distant objects, the user looks higher, through the portion of the bifocals corrected for far-vision.
Efforts have been made to treat presbyopia using partitioned lenses positioned directly over the pupil of the eye. Examples include multifocal contact lenses. Unfortunately, when presbyopia is corrected with bifocal or multifocal lenses attached to the cornea, the user is simultaneously looking through the near- and far-vision corrected lenses. As a result, the user will see both in-focus and out-of-focus images simultaneously when viewing an object. This out-of-focus image superimposed on the in-focus image can cause glare and degrade vision when viewing objects at low contrast.
Another technique for treating presbyopia has been to correct one eye of the patient for near-vision and to correct the other eye for distance-vision. This technique is known as monovision. With monovision, a patient uses one eye to see distant objects and the other eye to see close objects. Unfortunately with monovision, the patient may not clearly see objects that are intermediately positioned because the object is out-of-focus for both eyes. Also, a patient may have trouble seeing with only one eye.
Laser-based systems and methods are known for enabling ophthalmic surgery on the cornea in order to correct vision defects by the technique known as ablative photodecomposition. Changing the shape of the anterior surface of the cornea will change the optical properties of an eye. These ablative photodecomposition systems and methods control ultraviolet laser radiation flux density and exposure time upon the cornea so as to achieve a desired surface change in the cornea and thereby correct an optical defect.
Several different ablative photodecomposition techniques have been described to correct specific optical errors of the eye. For example, a myopic condition may be corrected by laser sculpting a corneal surface to reduce curvature. An astigmatic condition, which is typically characterized by a cylindrical component of curvature (departing from the otherwise generally spherical curvature of the cornea), can be corrected by a cylindrical ablation. Laser sculpting a corneal surface to increase the curvature can correct a hyperopic condition.
In a typical laser surgical procedure, the optically functional region of the corneal surface to be ablated is designated the optical zone. Depending on the nature of the desired optical correction, the optical zone may or may not be centered on the center of the pupil or on the apex of the anterior corneal surface. One technique for increasing the curvature of the optical zone for hyperopia error correction involves selectively varying the area of the cornea exposed to the laser beam radiation so as to produce an essentially spherical surface profile of increased curvature. This selective variation of the irradiated area may be accomplished in a variety of ways. For example, the optical zone can be scanned with a laser beam having a relatively small cross-sectional area (compared to the optical zone) in such a manner that the ablation depth increases with distance from the intended center of ablation. The result is a substantially spherical profile for the anterior corneal surface with maximum depth of cut at the extreme outer boundary of the optical zone. Another technique for sculpting the optical zone employs a rotatable mask having a plurality of apertures. The apertures are sequentially introduced into the laser beam path to provide progressive shaping of the laser beam in order to achieve the desired profile.
Efforts have also been made to treat presbyopia using ablative photodecomposition. One specific technique of treating presbyopia creates near-vision correction by ablating a region of the lower portion of the cornea adjacent the pupil rim. With this eccentric positioning of the ablation, the near-vision lens is not centered over the pupil. Consequently, constriction of the pupil may occlude the ablated near-vision lens. Constriction of the pupil is a natural response of the eye to illumination, and could potentially disrupt near-vision.
Alternative suggested presbyopia treatments include laser ablation of a small annular region of the cornea (having a diameter not exceeding 3.5 mm), or the ablation of a central lens for near-vision, surrounded by a gradual blend zone, and then a peripheral far-vision lens, all within the optically used portion of the cornea.
Efforts have been made in the past to laser sculpt a transition zone to provide a more gradual sloping of the walls and to eliminate the sharp discontinuity between the ablation zone and the surrounding untreated cornea. These efforts have included the use of a beam rotation or scanning mechanism operated by a computer to provide programmed ablation of the transition zone to achieve a sigmoid or other profile. While somewhat effective, these efforts often suffer from the added complexity of additional optical elements, such as a rotatable off-axis mirror or revolving prism having suitable optical properties.
2. Description of the Background Art
Systems and methods relevant to laser-based treatments for presbyopia are disclosed in the following U.S. patents and patent applications, the entire disclosures of which are hereby incorporated by reference: U.S. Pat. No. 5,395,356, issued Mar. 7, 1995, entitled “Correction of Presbyopia by Photorefractive Keratectomy”; U.S. Pat. No. 5,533,997, issued Jul. 9, 1996, entitled “Apparatus and Method for Performing Presbyopia Correction”; and U.S. Pat. No. 5,314,422, issued May 24, 1994, entitled “Equipment for the Correction of Presbyopia by Remodeling the Corneal Surface by Means of Photoablation.”
Ablative photodecomposition systems and methods are disclosed in the following U.S. patents and patent applications, the entire disclosures of which are hereby incorporated by reference: U.S. Pat. No. 4,665,913, issued May 19, 1987, entitled “Method for Ophthalmical Surgery”; U.S. Pat. No. 4,669,466, issued Jun. 2, 1987, for “Method and Apparatus for Analysis and Correction of Abnormal Refractive Errors of the Eye”; U.S. Pat. No. 4,732,148, issued Mar. 22, 1988, entitled “Method for Performing Ophthalmic Laser Surgery”; U.S. Pat. No. 4,770,172, issued Sep. 13, 1988, entitled “Method of Laser Sculpture of the Optically Used Portion of the Cornea”; U.S. Pat. No. 4,773,414, issued Sep. 27, 1988, entitled “Method of Laser Sculpture of the Optically Used Portion of the Cornea”; U.S. patent application Ser. No. 07/109,812, filed Oct. 16, 1987, entitled “Laser Surgery Method and Apparatus”; U.S. Pat. No. 5,163,934, issued Nov. 17, 1992, entitled “Photorefractive Keratectomy”; U.S. Pat. No. 5,556,395, issued Sep. 17, 1996, entitled “Method and System for Laser Treatment of Refractive Error Using an Offset Image of a Rotatable Mask”; U.S. patent application Ser. No. 08/368,799, filed Jan. 4, 1995, entitled “Method and Apparatus for Temporal and Spatial Beam Integration”; U.S. patent application Ser. No. 08/058,599, filed May 7, 1993, entitled “Method and System for Laser Treatment of Refractive Errors Using Offset Imaging”; U.S. Pat. No. 5,683,379, issued Nov. 4, 1997, entitled “Apparatus for Modifying the Surface of the Eye Through Large Beam Laser Polishing and Method of Controlling the Apparatus”; and U.S. Pat. No. 5,827,264, issued Oct. 27, 1998 entitled “Method of Controlling Apparatus for Modifying the Surface of the Eye Through Large Beam Laser Polishing.”
Techniques for treating presbyopia with contact lenses are disclosed in the following U.S. patents and patent applications, the entire disclosures of which are hereby incorporated by reference: U.S. Pat. No. 5,835,192, issued Nov. 10, 1998, entitled “Contact Lens and Method of Fitting a Contact Lens”; U.S. Pat. No. 5,485,228 issued Jan. 16, 1996 entitled “Multifocal Ophthalmic Lens Pair;” and U.S. Pat. No. 5,864,379 issued Jan. 26, 1999 entitled “Contact Lens and Process for Fitting.”BRIEF SUMMARY OF THE INVENTION
It is an object of the invention to mitigate and/or inhibit presbyopia with minimal vision degradation by ablating a transition zone peripheral to an optical zone. It is a further object of the invention to ablate a cornea to produce a healed cornea with an aspheric optical zone that corrects presbyopia. In one aspect, the invention provides for ablating the cornea to a desired shape that compensates for changes in the corneal shape as the cornea heals. In another aspect, the invention provides for the simultaneous correction of presbyopic and other refractive corrections such as nearsightedness, farsightedness and astigmatism. In a yet further aspect, the invention provides for scaling the aspheric optical zone to match the size of the pupil. In yet another aspect, the invention provides for a method for treating presbyopia which includes ablating a transition zone outside an optical zone.
One of the major difficulties encountered in the application of laser surgery techniques to effect hyperopic and presbyopic refractive error corrections lies in the nature of the boundary between the optical zone and the untreated area. When the anterior surface of the cornea is sculpted to have an increased curvature, the maximum depth of cut occurs at the outer boundary of the optical zone. The generally annular region between this outer boundary and the adjacent untreated anterior surface portion of the cornea typically exhibits steep walls after the completion of the photoablation procedure. After the surgery, the eye tends to eliminate these steep walls with a stimulated healing response involving concurrent epithelial cell growth and stromal remodeling by the deposition of collagen, which results in corneal smoothing by filling in tissue in the steep walled region. This natural healing response acts to eliminate the discontinuity, resulting in a buildup of tissue in the steep walled region and over the outer portion of the optical zone. This natural phenomenon, sometimes termed the “hyperopic shift” in phototherapeutic keratectomy, causes a lack of precision for a given surgical procedure and diminished predictability, counteracting the beneficial effects of the refractive correction procedure and thereby reducing the desirability of the procedure to the prospective patient.
According to the present invention, the ablated surface can be contoured to provide an aspheric surface on a healed cornea. The invention provides for adjusting the ablation to compensate for factors effecting the final geometry of the healed cornea. These factors include corneal healing and the spatial variation of ablation. The shape of tissue ablated with a uniform laser beam pulse will depend upon the size and shape of the laser beam spot. The spatial variation of the total ablation may also cause variations in the ablated corneal shape. For example, a hyperopic ablation intended to produce a spherical ablation may demonstrate greater steepening near the center of the optical zone. This increased central curvature may form an aspheric surface that corrects for presbyopia.
The ablated surface is covered following the surgery, typically by a new epithelial layer or a repositioned anterior flap of the corneal tissue. Consequently, the final shape of the anterior surface of the cornea may be a different shape than the ablated shape. However, it is the final change in shape of the anterior surface of the cornea, not the initial ablated surface, which determines the refractive change effected by the surgery. Therefore, it may be desirable to ablate a shape on the cornea that is different from the final intended shape on the anterior surface of the cornea. For example, the optical zone may be ablated to a substantially spherical shape for correcting hyperopia. This ablated surface may then heal to an aspheric surface that corrects presbyopia.
The invention includes a method and system for performing ablative photodecomposition of the corneal surface that is capable of providing relatively smooth transition zones along with accurate sculpting of the anterior or other corneal surface to effect simultaneous symmetric or asymmetric refractive and presbyopic corrections with relatively large area coverage. The invention preferably employs a laser beam of smaller beam size than the total treatment area.
The invention further provides for the ablation of an optical zone that substantially matches the area of the pupil. For presbyopic patients, the maximum pupil diameter is typically about 5 mm. Therefore, it is an aspect of the invention that the ablated optical zone have a diameter of about 5 mm, and be user selectable (by the user of the ablation system) to a diameter between 3 and 7 mm. The optical zone is preferably ablated to form a healed aspheric surface. Preferably, the central portion of the optical zone provides near-vision correction and the peripheral portion of the optical zone provides far-vision correction.
The invention additionally provides for scaling a diameter of the aspheric surface to the pupil. This scaling of the aspheric surface permits an appropriate balance between near and far-vision correction within the pupil. For example, a patient with a 5 mm diameter pupil may have a 2.5 mm diameter zone corrected for near-vision, while a patient with a 3 mm diameter pupil may have a 1.5 mm diameter zone corrected for near-vision. Scaling of the aspheric lens may be based on areas of the pupil and/or aspheric surface.
The invention also provides for ablating a transition zone peripheral to the optical zone and to the pupil. This positioning of the ablated transition zone will produce optimal results once the cornea heals. The ablated transition zone provides greater control over the healing process and provides greater control of the shape of the healed surface within the adjacent optical zone. Because the transition zone is ablated to control the shape of an adjacent healed surface, the transition zone may produce a corneal shape which corrects for neither near- nor far-vision. Thus, the transition zone is preferably positioned outside the pupil. Further, the transition zone is preferably sized so that healing of the cornea can be controlled within the adjacent optical zone. The optimal size of the transition zone is an annular region extending radially outward about 2 mm from the outer edge of the ablated optical zone. An ablation with a 5 mm diameter ablated optical zone and an optimally sized ablated transition zone will extend about 9 mm across the cornea. Transition zones of other sizes may be ablated outside the optical zone. Dimensions of the transition zone extending radially outward from the optical zone range from about 1 to 3 mm and preferably from about 1.5 to 2.5 mm.
In a first aspect, the present invention provides a method for reprofiling an anterior surface of the cornea of the eye. The anterior surface is reprofiled from an initial shape to a multifocal aspheric shape for correcting presbyopia. The method comprises aligning a laser system with the eye. The laser system is operable to deliver ablative radiation to the cornea. A surface of the cornea is ablated to a desired shape by selectively exposing the cornea to the ablative radiation. The cornea is ablated to an ablated shape so that an optical zone extends across the pupil and so that a transition zone is disposed beyond the pupil. The ablated surface is covered to produce a final aspheric anterior corneal surface.
In some embodiments, the covering step will comprise regenerating an epithelial layer over an ablated anterior surface of the cornea. In other embodiments, the covering step will comprise repositioning a flap of the cornea over the eye after a portion of either the flap, or the underlying corneal tissues, has been ablated.
In another aspect, the present invention provides an ophthalmic surgery system for performing selective ablation of a corneal surface of the eye so as to create a desired aspheric shape for correcting presbyopia on the anterior surface of a healed cornea. The system comprises means for directing a laser beam along a path. Means are also provided for profiling the beam to produce a profiled beam with a center. Means for displacing the center of the profiled beam over an area of the corneal surface will generally be coupled to the profiling means. A computer controls the positioning of the beam center over the area, and creates a plurality of successive laser beam pulses. The position of the plurality of pulses is determined by a laser treatment table that is scaled to a dimension of a pupil.
In another aspect, the present invention provides a laser eye surgery method comprising selectively ablating corneal tissue from an eye having an uncorrected surface shape. Corneal tissue is ablated so as to produce an initial ablated shape on an anterior surface of the cornea of the eye. The ablated eye heals, and the healed eye has a healed anterior surface shape which differs significantly from the initial ablated shape. This healed shape substantially, and in some instances entirely, corrects a refractive error of the eye.
In yet another aspect, the present invention provides a laser eye surgery method comprising selectively ablating corneal tissue from an eye having a refractive error. The refractive error is selected from the group consisting of myopia, hyperopia, and astigmatism. The ablating step removes a portion of cornea so as to simultaneously correct the refractive error and mitigate presbyopia of the eye.
In yet another aspect, the present invention provides a method for treating presbyopia of an eye. The eye has a pupil, and the method comprises selectively ablating corneal tissue from the eye so as to produce an ablated corneal surface. The corneal surface has an optical zone, and a transition zone surrounding the optical zone. The optical zone of the corneal surface defines an aspheric shape to mitigate the presbyopia, and a dimension of the optical zone substantially matches a dimension of the pupil under scotopic conditions.
In yet another aspect, the present invention provides a method for treating presbyopia of an eye. The eye has a pupil, and the method comprises selectively ablating corneal tissue from the eye so as to produce a corneal surface having an optical zone, and a transition zone surrounding the optical zone. The optical zone of the corneal surface defines an aspheric shape to mitigate the presbyopia. The transition zone is disposed outside of the pupil.
For a fuller understanding of the nature and advantages of the invention, reference should be had to the ensuing detailed description taken in conjunction with the accompanying drawings.
Turning now to the drawings,
While the present invention will often be described with reference to the mitigation of presbyopia in combination with refractive hyperopia treatment, it should be understood that the benefits of the present invention are not limited to these specific procedures. These presbyopia treatment techniques may be used when no other refractive correction (other than the correction, mitigation, and/or inhibition of presbyopia) is desired, or the present treatment may be combined with therapies for one or more of myopia, astigmatism, irregular refractive aberrations, and the like, as well as with hyperopia. Still other aspects of the present invention, including methods and systems which accommodate and adjust for re-epithelization, may find uses in a broad variety of ophthalmic procedures.
The peripheral positioning of the far-vision correction advantageously permit distance viewing when the pupil is dilated at night. Anterior transition surface 215 is the anterior surface of the cornea that provides a gradual change in shape between anterior optical surface 210 and the portion of the cornea retaining the initial anterior surface 205. The outer boundary 212 of the anterior optical surface preferably extends entirely across, and is ideally substantially coextensive with, the pupil which is bounded by iris 220. The light rays passing through anterior transition surface 215 do not contribute to the image formed by anterior optical surface 210. Therefore, anterior transition surface 215 is desirably positioned outside the pupil. This positioning of anterior transition surface 215 causes the light rays passing through anterior transition surface 215 to be substantially occluded by iris 220. This occlusion improves patient vision because the light rays are blocked that do not contribute to image formation, and which would otherwise reduce the contrast of the image.
The optical correction effected by an ablative surgical procedure to the cornea is derived from a change in the anterior corneal surface from an initial anterior surface 205 to post-operative anterior optical surface 210. The anterior optical correction is the post-operative anterior optical surface 210 minus the initial anterior surface 205. An ablation profile is a change in an exposed surface profile occurring immediately after the tissue removal process. Therefore, the ablation profile is the exposed surface profile immediately after the tissue removal process minus the initial exposed surface profile. As used herein, “ablated shape” can refer either to an ablation-induced change in a surface topography on a surface of the cornea, or to the surface topography of the cornea after ablation. Similarly, “healed shape” can mean either a final corneal topography once healing is complete, or a change in the corneal topography from an initial topography to a final corneal topography once healing is complete. A healed shape differs significantly from an ablated shape when a difference between the two shapes is sufficient to be perceptible by a patient. Healing can refer either to an initial covering of an ablated surface contour or changes in a tissue structure of the cornea following an initial covering of an ablated surface contour.
The relationship of the ablated surface and the anterior corneal surface overlying the ablated surface is shown in
In one embodiment, covering of the ablated shape will cause the final shape of anterior optical surface 210 of the anterior surface of cornea 200 to be different from ablated optical zone 211. This aspect of the present invention is more fully described in the publication entitled “Corneal Ablation Profilometry and Steep Central Islands,” Journal of Refractive Surgery, 1997, Vol. 13, pp. 235-45, the entire disclosure of which is herein incorporated by reference.
Initial ablated shape 202 is covered after the ablation. Proximity to ablated transition zone 216 may cause anterior peripheral optical surface 240 to be a different shape than underlying ablated peripheral optical zone 241. However, anterior central optical surface 230 of anterior optical surface 210 is distant from ablated transition zone 216. Therefore the shape of anterior central optical surface 230 will more closely match the shape of ablated central optical zone 231. In one aspect, the covering may include regeneration of the epithelial layer following ablation of Bowman's membrane and adjacent stromal layers. In another aspect, covering includes replacing a resected portion of the cornea as is described in U.S. Pat. No. 4,903,695, issued Feb. 27, 1990, entitled “Method and Apparatus for Performing a Keratomileusis or the Like Operation.” In this aspect, the resected portion includes an epithelial layer. In a yet further aspect of covering, a tear film forms over the epithelial layer to form the anterior surface when cornea 200 is fully healed. The final shape of anterior optical surface 210 will substantially determine the optical properties of the cornea. Therefore, it may be desirable to ablate cornea 200 to form ablated optical zone 211 that is a different shape than the shape of anterior optical surface 210.
In another embodiment, ablated optical zone 211 includes ablated central optical zone 231 and ablated peripheral optical zone 241. Ablated intermediate optical zone 241 may be replaced by extending ablated peripheral optical zone 241 and ablated central optical zone 231 to border one another. Ablated central optical zone 231 provides about 2.5 D of near-vision correction with a range from about 0.5 to 4 D, preferably about 2 to 3 D and a diameter from about 1.0 to 3.5 mm and preferably from about 2 to 3 mm. Ablated peripheral optical zone 241 is ablated to provide far-vision correction and is sized to extend radially outward from the outer boundary of ablated central optical zone 231 to a diameter of about 5 mm with a range from about 3 to 7 mm and preferably from about 4 to 6 mm. Ablated transition zone 216 extends radially outward from the outer boundary of ablated optical zone 211 to a diameter of about 9 mm with a range from about 6 to 11 mm and preferably from about 7 to 10 mm. Covering of ablated optical zone 211 will cause anterior intermediate optical surface 240 to form over the border between ablated central optical zone 231 and ablated peripheral optical zone 241. Anterior central optical surface 230 will form over ablated central optical zone 231. Anterior peripheral optical surface 240 will form over ablated peripheral optical zone 241. Therefore, anterior optical surface 210 may be formed as a multifocal aspheric surface on cornea 200 by ablating only two optical zones within ablated optical zone 211.
An illustrative plot of the relative refractive power of anterior optical surface 210 as a function of radial position across the pupil is shown in
In an exemplary embodiment, ablated central optical zone 231, ablated intermediate optical zone, 236 and ablated peripheral optical zone 241 are scaled to match a dimension of the pupil. The scaling dimensions may be an area of the pupil, a diameter of the pupil, a radius, or the like. For example, ablated optical zone 211 may be decreased by about 20% from a diameter of about 5 mm to 4 mm for a patient with a 4 mm diameter pupil. In this case, ablated central optical zone 231, ablated intermediate optical zone 236 and ablated peripheral optical zone 241 are each decreased by about 20%. This scaling is desirable because it keeps the ratios of near, intermediate and far-vision nearly constant for varying pupil size. The inner boundary of ablated transition zone 216 is scaled to border the outer boundary of ablated optical zone 211. During the scaling of ablated optical zone 211, the outer boundary of ablated transition zone 216 may be scaled to match the scaling of ablated optical zone 211. Alternatively, the outer boundary of ablated transition zone 216 may be fixed to a constant value while the inner boundary of ablated transition zone 216 is varied.
The iris motor 23 is used to control the diameter of a variable diameter iris schematically depicted in
The system of
With reference to
The manner in which the slit width and diameter are varied by the computer depends upon the type of vision correction desired. For a hyperopic correction, a fixed value of the refractive correction may be used to generate the cut profile C(r). For a hyperopic refractive correction of a given fixed value, the sequencing of the aperture is done in such a manner as to satisfy the hyperopic lens equations described in “Photorefractive Keratectomy: A Technique for Laser Refractive Surgery” authored by Munnerlyn et al., J. Cataract Refract. Surg. Vol. 18, pages 46-52 (January 1988), the entire disclosure of which is hereby incorporated by reference. Also, European Patent Office publication number EP 0 628 298 A1, published Dec. 14, 1994, discloses an aperture sequencing for correcting hyperopia, the entire disclosure of which is hereby incorporated by reference.
For the correction of presbyopia, it may be desirable to vary the refractive power across the ablated surface. The cut profile C(r) may be calculated by calculating the incremental cut profiles along the surface. The incremental cut profiles are then summed to calculate the overall cut profile C(r). The incremental cut profiles may be calculated using the above hyperopic lens equation, the desired ablated refractive correction, and the position from the center of the aspheric lens.
The cut profile is given by the equation:
where ni is the number of laser pulses for the ith aperture in a sequence of aperture dimensions and radial positions, and d is the amount of material removed with each laser pulse or a scaling factor which also takes into account corneal healing. Once the cut profile has been calculated, the sequence of aperture dimensions and pulses may be calculated. The sequence of aperture dimensions is created by control of the width of the slit and the diameter of iris 32 throughout the surgical procedure. The sequence of aperture dimensions and positions are preferably incorporated into a laser treatment table.
The sequence of aperture dimensions may also be tailored to accommodate variations in the ablation profiles of individual pulses from the laser beam. For example, the spatial variation of tissue ablation may cause the geometry of tissue ablated with a single laser pulse to be deeper at the edges of an ablation adjacent the image of iris 32 and cylinder blades 35 and 36. For an individual laser pulse, this increased ablation depth near the edge of an ablation may be 50% greater than the central ablation depth. Therefore, a 4 D intended hyperopic ablation that assumes a uniform layer of tissue is removed with each laser pulse will ablate about 6 D of correction near the center of ablated optical zone 211. Clinically, the inventors have observed that patients treated with the above ablation algorithm for 3 to 4 D of hyperopia have also been successfully treated for presbyopia. However, with a +2 D correction, the correction of presbyopia is only partial. Therefore to correct presbyopia and hyperopia, it may be desirable to combine the +2 D correction with an aspheric ablation. In this case, the aspheric correction is about one half of the aspheric correction that would be ablated on an eye with no refractive error.
Preferably, the refractive correction of cut profile C(r) is scaled to match a dimension of the pupil. This scaling may be achieved by appropriately varying the refractive correction entered into the hyperopic lens equation. For example, consider the scaling of an ablation for a 5 mm pupil compared to a 4 mm pupil. If the aspheric surface includes a 1.5 D ablated curvature 1.25 mm from the aspheric lens center for the 5 mm pupil, this 1.5 D curvature will be ablated 1.0 mm from the aspheric lens center on a 4 mm pupil. This scaling maintains a balance of near and far-vision correction by accommodating individual variability in pupil size. By scaling the cut profile C(r), the scaling of the ablated optical zone is incorporated into the laser treatment table.
For the example shown in
The image of the aperture is now ready to be scanned over the anterior surface of the cornea. While several different scanning sequences are possible, the following sequence has been actually implemented with effective results. The radial position along the optical zone is broken into a series of discrete, equidistant (typically 0.1 mm apart) nodes. The number of pulses required to ablate tissue to cut depth C(r) at a node adjacent to the edge of the inner slit is calculated using
where n is the number of pulses, δC(rn) is the difference between the actual ablation depth from previous pulses and the desired ablation depth at the node, θi (rn) is the half angle coverage of the aperture at rn as previously defined. The radial ablation profile from previous pulses is calculated by summing the ablation depth from previous positions and pulses at each node as described by equation I. For the initial position, δC(rn)=C(r). The number of pulses required for each subsequent node is calculated for each node adjacent to the inner cylinder blade as the blade moves toward the edge of the optical zone. Having determined the correct number of pulses at each node, the treatment must be smoothed rotationally to ensure that it is correct and free from aberrations.
The invention affords great flexibility in performing various types of corrections by virtue of the fact that the system can be programmed to accommodate patients having differently sized physical eye parameters and refractive and presbyopic correction requirements. The variable slit width/variable diameter iris arrangement is particularly adaptable for use in the simultaneous treatment of presbyopia, hyperopia, hyperopic astigmatism and irregular refractive aberrations. For simultaneous treatment of presbyopia, hyperopia and hyperopic astigmatism, the ablation geometry is solved as a function of radial displacement and angular position of the aperture image about the rotational center. Further, in all procedures requiring a smoothing of the transition zone at the periphery of the ablation zone, the diameter of the iris is varied over a predetermined range along with the slit width variation. For presbyopia and refractive aberrations, a device such as a spatially resolved refractometer or a topography machine or both may be used to map the irregular surface contour of the cornea to determine the exact surface corrections required. Thereafter, the slit width and the iris diameter can be programmed such that corneal sculpting will achieve the desired aspheric surface geometry on a healed cornea. Alternatively, a wavefront sensor may be used to map the irregular refractive aberrations of the eye. One suitable embodiment of such a wavefront sensor is the Hartmann-Shack sensor described in U.S. Pat. No. 5,777,719, the entire disclosure of which is herein incorporated by reference.
For any of the above specific correction procedures, a treatment table is normally constructed. The treatment table contains the value of all of the discrete radial and angular positions of the optomechanical elements used to scan the image over the relevant portion of the anterior corneal surface. This table also contains the number of laser pulses per position. A typical treatment table contains on the order of about 500 different entries.
The treatment table for a given procedure may incorporate special features designed to improve the efficiency of the procedure. For example, for some procedures (e.g., simultaneous hyperopic and presbyopic correction) it can be beneficial to leave a small zone centered on the optical zone untreated. This can be done by constraining motion of the inner cylinder blade to guarantee occlusion in the small zone of interest. The diameter of the untreated zone varies from about 0.1 to 1.5 mm, is preferably from about 0.5 to 1.0 mm and is ideally about 0.7 to 0.9 mm. Also, standard tables can be constructed for a specific procedure—e.g., hyperopic correction-to different Dioptric correction values, and these standard tables can be sorted and combined to perform multiple repetitions of one or more standard tables to effect a given Dioptric correction. For example, standard tables may be created for a myopic correction for values of ¼, ½ and 1 Diopter. Using these tables, a 3.75 Diopter correction would proceed by performing the standard 1 Diopter correction three times, followed by the ½ Diopter correction and the ¼ Diopter correction.
While the invention has been described above with specific reference to ablation of an anterior corneal surface, various portions of the cornea may also be treated using the invention. For example, the epithelium may be mechanically removed by scraping, as is typically done in photorefractive keratectomy, and the exposed surface may be ablated. Further, the invention can also be used for laser keratomileusis of corneal lamella removed from the cornea. This procedure is described in U.S. Pat. No. 4,903,695, issued Feb. 27, 1990, entitled “Method and Apparatus for Performing a Keratomileusis or the Like Operation.”
In applying the invention to this procedure, a flap of corneal tissue is physically removed (either fully or partially) from the cornea, the size of the removed portion typically lying in the range from about 8 to 10 mm wide and a variable thickness up to 400 microns. This flap of tissue is typically removed using a microkeratome. Next, the flap is placed in a suitable fixture—typically an element having a concave surface—with the anterior surface face down. Thereafter, the required ablation is performed on the reverse exposed surface of the flap, after which the ablated flap is repositioned on the cornea. Alternatively, after the flap is removed from the cornea, the exposed stromal tissue of the eye can be ablated according to the invention, after which the flap is reattached over the freshly ablated stromal tissue.
The technique of shaping a cornea is further illustrated in
The covering and healing of the ablated surface decrease the difference between the intended optical correction and the anterior corneal surface optical correction as illustrated in
The effect of the covering and corneal healing of an ablated optical zone is illustrated in
By estimating a healing-induced change, an initial ablated surface shape may be derived from a desired anterior corneal surface shape and a healing-induced change as illustrated in
The ablated shape may be restricted or reduce relative to a desired anterior surface correction to obtain the desired anterior surface correction. The diameter of the relative restriction is between about 0.1 and 2 mm, preferably between about 0.2 and 1 mm and is ideally between about 0.3 and 0.7 mm. In an exemplary embodiment this restriction is about 0.5 mm as illustrated in
In some instances, it may be desirable to treat presbyopia by leaving a central region of the optical zone untreated as illustrated in
The above techniques can be used to calculate initial ablation shapes for treating conditions besides hyperopia and presbyopia. These techniques may be used to calculate the initial ablation shapes used to treat astigmatism, myopia and irregular refractive aberrations of the eye. For example, the higher order aberration terms of an irregular refractive aberration may be over corrected on an ablated corneal surface to form an anterior surface on a healed cornea with a desired optical correction of the higher order aberrations.
The above technique of making a multifocal optical correction on the anterior surface of the cornea can be applied to both eyes of a patient to provide an improved correction of presbyopia with binocular vision. The correction of presbyopia preferably covers about a 3 D range. However, with binocular vision this approximately 3 D range of presbyopia correction may be treated by treating each eye with a multifocal optical correction having less than the full 3 D range of presbyopia correction. In this case, the average refraction of each of the two eyes is different to provide clear vision over the full 3 D range. A first eye is corrected for near-vision, and a second eye is corrected for distance vision. The multifocal anterior optical surface provides improved focus for objects intermediate to near and far-vision. For example, one eye is treated to have an average refraction of −0.75 D with a 1.5 D multifocal range of focus. This eye has an effective focus from 0 to −1.5 D. The other eye is treated to have an average refraction of about −2.25 D with a 1.5 D multifocal range of focus. This eye has an effective focus from about −1.5 D to −3 D. The effective range of focus of the two eyes combined is about 3 D. The multifocal range on each eye varies between about 0.5 and 2.0 D, and is preferably between about 1.0 and 1.5 D. The difference between the average refraction of the two eyes varies between about 0.5 and 2.5 D, and is preferably between about 1 and 2 D.
While the above provides a full and complete disclosure of the preferred embodiments of the invention, various modifications, alternate constructions and equivalents may be employed as desired. For example, while the invention has been described with specific reference to the system of
1. A method of treating a first eye and a second eye of a patient to mitigate presbyopia, the method comprising:
- providing a presbyopia correction covering a desired optical power range by: correcting the first eye to have a first average refraction and a first range of focus, the first range of focus being less than the desired optical power range; correcting the second eye to have a second average refraction and a second range of focus, the second range of focus being less than the desired optical power range;
- wherein the first range and the second range of focus combine to provide focus throughout the desired optical power range.
2. The method of claim 1, wherein the first average refraction differs with the second average refraction by 0.5 D to 2.5 D after correction.
3. The method of claim 2, wherein the first average refraction differs with the second average refraction by 1 D to 2 D after correction.
4. The method of claim 1, wherein the first eye is corrected for far vision.
5. The method of claim 3, wherein the second eye is corrected for near vision.
6. The method of claim 1, wherein the desired optical power range is between a 1 D range and a 4 D range.
7. The method of claim 1, wherein the desired optical power range is about a 3 D range.
8. The method of claim 5, wherein the first range of focus for the first eye is between a 0.5 D range and a 2.0 D range after correction.
9. The method of claim 8, wherein the first range of focus for the first eye is between a 1.0 D range and a 1.5 D range after correction.
10. The method of claim 8, wherein the first average refraction for the first eye is between 0.25 D and −1.75 D after correction.
11. The method of claim 10, wherein the first average refraction for the first eye is about plano after correction.
12. The method of claim 6, wherein the second range of focus for the second eye is between a 0.5 D range and a 2.0 D range after correction.
13. The method of claim 12, wherein the second range of focus for the second eye is between a 1.0 D range and a 1.5 D range after correction.
14. The method of claim 13, wherein the second average refraction for the second eye is between −1.25 D and −2.25 D after correction.
15. The method of claim 14, wherein the second average refraction for the second eye is about −1.5 D after correction.
16. A system for reshaping a first eye and a second eye of a patient to mitigate presbyopia, the system comprising:
- a laser for generating an electromagnetic radiation beam;
- an optical scanning system for directing the electromagnetic radiation beam along a beam path; and
- a processing system coupled with the laser and the optical scanning system, the processing system configured to provide a presbyopia correction covering a desired optical power range by: identifying a first aspheric shape modification for the first eye and a second aspheric shape modification for the second eye, the first aspheric shape modification providing a first average refraction and a first range of focus to the first eye, and the second aspheric shape modification providing a second average refraction and a second range of focus for the second eye, the first range of focus and the second range of focus each being less than the desired optical power range; and wherein the first range of focus and the second range of focus combine to provide focus throughout the desired optical power range.
17. The system of claim 16, wherein the first aspheric shape modification corrects the first eye for far vision and wherein the second aspheric shape modification corrects the second eye for near vision.
18. The system of claim 17, wherein the first range of focus for the first eye and the second range of focus for the second eye is between a 1.0 D range and a 2.0 D range after correction.
19. The system of claim 18, wherein the first average refraction for the first eye is between 0.25 D and −0.75 D after correction and wherein the second average refraction for the second eye is between −1.25 D and −2.25 D after correction.
20. A method of treating a first eye and a second eye of a patient to mitigate presbyopia, the method comprising:
- providing a presbyopia correction covering at least a 3 D range by: correcting the first eye to have a 0.25 D to a −0.75 D average refraction and at least a 1.5 D range of focus; correcting the second eye to have a −1.25 D to a −2.25 D average refraction and at least a 1.5 D range of focus;
- wherein the at least 1.5 D range of focus for the first eye and the at least 1.5 D range of focus for the second eye combine to provide focus throughout the at least 3 D range.
Filed: Aug 5, 2013
Publication Date: Apr 10, 2014
Applicant: AMO Manufacturing USA, LLC (Santa Ana, CA)
Inventors: Marc Odrich (Riverdale, NY), Kenneth Greenberg (Ridgefield, CT), Jerome A. Legerton (San Diego, CA), Charles R. Munnerlyn (San Jose, CA), John K. Shimmick (Belmont, CA)
Application Number: 13/958,799
International Classification: A61F 9/008 (20060101);