HK1164100B - Method and apparatus for universal improvement of vision - Google Patents

Description

Method and apparatus for overall improvement of vision

The present application is a divisional application of a patent application having an application date of 2007, 3 and 8, and an application number of 200780016536.0, entitled "method and apparatus for improving eyesight in general".

Technical Field

The present invention relates generally to methods and devices for improving eye vision, and more particularly to methods and devices for improving vision at all distances (hereinafter referred to as "global improvement").

Background

The most common defects in human vision are caused by the inability of the eye to focus incident light to a common focal point on the retina. For example, myopia may be due to the eye focusing light in front of the retina, hyperopia may be due to the eye focusing incident light behind the retina, and astigmatism may be due to the eye not having a common focus. Human optical scientists often model the cornea as a portion of an ellipsoid defined by orthogonal major and minor axes.

Today, vision is often improved in one of two ways: a lens is placed in front of the eye (e.g., contact lenses or spectacle lenses) or within the eye (e.g., intraocular lenses) in order to properly refocus incident light into the eye. Alternatively, the shape of the effective outer surface of the cornea is altered, for example, by laser ablation surgery or other surgical means to alter the shape of the anterior surface of the cornea. Such surgical procedures for correcting visual acuity are generally directed to increasing or decreasing the surface curvature of the cornea. Some procedures are intended to change the shape of the cornea to be more spherical, while others are intended to change the shape of the cornea to an "average" ellipse, or more recently, to correct for it based on wavefront (wave front) analysis, which is a method intended to correct for the "higher order aberrations" of the eye.

Contact lenses or spectacle lenses are used to provide vision correction for objects of interest at different distances from the eye (e.g., objects relatively close to the eye or objects further from the eye). In this regard, different lens powers (lentiscopes) have been provided for different areas of the lens to allow the wearer to see objects at different distances. Conventional "multifocal" contact lenses are lenses in which there is a difference in optical power at different extents or regions of the lens surface. Such zones have been constructed to form spherical segments or spherical dihedral shapes of different optical powers on the lens. While such lenses have provided vision correction at certain distances, such lenses have not provided sufficient overall vision improvement to restore the natural visual acuity of the eye, which requires multiple levels of depth correction in addition to distance refractive error correction. Furthermore, variable focal length spectacle lenses have been provided in which a central optical zone is formed with a curvature that varies continuously with vertical position in order to provide vision correction over all distances. However, the wearer must raise or lower his head to make adjustments to the distance. Some contact lens designs provide two or more zones of refractive power in different circles (bands) on the anterior surface. Such lenses translate (translate) position according to the position of the eyelid. To provide clear vision with this conversion design, the wearer must likewise raise or lower his head in order to adjust for the distance of the object being viewed. Requiring the wearer to make such adjustments is not optimal.

It would be desirable to provide overall vision improvement without requiring any additional physical movement by the wearer.

Disclosure of Invention

From the surface modeling technique disclosed in U.S. patent No.5,807,381, using an analysis of clinical measurements, applicants have discovered that the cornea of an eye having an ideal "turtleback" shape will exhibit an overall improvement in vision if the surface curvature of the cornea of the eye is altered solely to correct for poor distance vision. As used herein, a "turtleback" shape will be understood to exhibit the flattest surface curvature at a point located at the edge closest to the nose, where the surface curvature is determined along a semi-meridian from that point on the cornea to a central point. Moving up and around the cornea periphery, the surface curvature will continuously increase until it reaches a maximum at the vertical end of the cornea (verticalextreme). The surface curvature will then decrease continuously until it reaches a median value at the edge of the cornea furthest from the nose, will increase continuously to a maximum at the vertically lowest edge of the cornea, and will decrease continuously until it returns to a minimum at the edge of the cornea closest to the nose.

According to the present invention, an overall improvement in vision is achieved by effectively changing the shape of the cornea to an ideal turtleback shape on which the necessary curvature adjustment is imposed to achieve vision correction for distant objects of interest. According to one embodiment, the cornea is actually altered to the desired shape by a corneal surgery, preferably a laser cutting surgery. According to a second embodiment, a contact lens is placed over the cornea, the contact lens having the desired turtleback shape for distance vision correction.

According to the present invention there is provided a method for improving or planning an improvement in eye vision, comprising the steps of: on a surface model of the cornea of the eye, focal points at different positions on the surface model are determined, and the model is modified so as to move the focal points to predetermined positions with respect to a predetermined reference axis without forcing them to move to a common point, the modified model representing a desired reconstruction of the cornea, wherein the modifying step represents an effective reshaping of the cornea by applying an optical lens to the eye intended to correct refractive errors.

Further according to the invention, there is provided an optical lens having an anterior surface, a posterior surface and an optical center on its anterior surface, the anterior surface having an M-wave shape such that the surface curvature measured along a curve passing through the optical center varies substantially as a smoothed letter M with respect to an angular direction about the optical center, wherein the 0 ° angular direction is substantially the point closest to the nose when the lens is worn and the central foveal point of M occurs substantially at the point furthest from the nose when the lens is worn corresponding to a 180 ° direction, the maximum values of M occur substantially at the vertically highest and lowest ends of the lens when the lens is worn corresponding to 90 ° and 270 ° directions respectively, wherein the curve passing through the optical center on the anterior surface of the lens defines on the anterior surface focal zones corresponding to different positions on the corneal surface of the eye, each focal zone is shaped to move the focus of the corresponding location of the cornea to a predetermined position relative to a predetermined reference axis in the eye without forcing the focus of each zone to a common point.

The present invention also provides a method of determining a required change in shape to the cornea of an eye, the method being performed with the aid of a computer system comprising a display device, the method comprising the steps of: modeling an anterior corneal surface as a surface model tailored to an M-wave shape such that surface curvature measured along a curve passing through an optical center varies substantially as a smoothed letter M in relation to an angular direction about the optical center, wherein the 0 ° angular direction is substantially the point closest to the nose when the lens is worn and the M's central foveal point occurs substantially at the point farthest from the nose when the lens is worn corresponding to a 180 ° direction, the M's maximum value occurs substantially at the vertically highest and lowest ends of the lens when the lens is worn corresponding to 90 ° and 270 ° directions, respectively; viewing the surface model on the display device: generating a first signal configured to control another apparatus to shape a contact lens so that an anterior surface of the lens has the M-wave shape; or generating a second signal configured to control the device according to the M-wave shape, wherein the curve modeling the front surface and passing through the optical center defines different focal regions, the method further comprising the steps of: in the modeling step the focal points of the different focal zones are determined and the model formed by the modeling step is modified such that the focal points are moved to predetermined positions relative to a predetermined reference axis without forcing them to move to a common point, the modified model representing a desired reconstruction of the cornea.

Drawings

The foregoing brief description and further objects, features and advantages of the invention will be more fully understood in connection with the following detailed description of the presently preferred embodiments, taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a block diagram illustrating a method of achieving vision correction by laser cutting of the cornea or an appropriately shaped corrective lens in accordance with the present invention;

FIG. 2 is a schematic diagram illustrating a planar image of a point cloud obtained by a corneal image acquisition system;

FIG. 3 is a schematic plan view similar to FIG. 2 illustrating a plurality of splines and how they connect data points through the point cloud;

FIG. 4 is a perspective view of a corneal matching surface (matringsurface) illustrating how a characteristic curve is constructed;

FIG. 5 is a graph illustrating axial focus astigmatism of a cornea at a 3mm diameter;

FIG. 6 illustrates radial focus astigmatism corresponding to FIG. 5;

FIG. 7 is a graph illustrating axial focus astigmatism of the cornea at 5mm diameter;

FIG. 8 illustrates radial focus astigmatism corresponding to FIG. 7;

FIG. 9 is a graph illustrating axial focus astigmatism of the cornea at 7mm diameter;

FIG. 10 illustrates radial focus astigmatism corresponding to FIG. 9;

FIG. 11 illustrates a method of modifying a corneal model by being orthogonal to a central axis;

FIG. 12 illustrates the concept of off-center (centered) orthogonalization;

FIGS. 13-15 are plan views illustrating a macula of 72 foci P distributed in spiral, rose (rose) and double rose patterns, respectively, on an anterior surface of the macula (macula); and

fig. 16 illustrates three waveforms useful in describing an ideal turtleback adjustment of the cornea that provides overall vision improvement.

Detailed Description

In connection with modern corneal surgery, such as corneal ablation surgery, for clinical applications and for the design and manufacture of contact lenses, high resolution cameras are used to obtain a digitized array of discrete data points on the corneal surface. One system and camera that has been available for mapping (map) the cornea is the PAR corneal mapping system (PARCTS) of the PAR vision system (parvision system). PARCTS maps corneal surface topology in three-dimensional cartesian space, i.e., along an x-coordinate, a y-coordinate, and a depth (Z) -coordinate.

The "line-of-sight" is a straight line segment from a fixed point to the center of the entrance pupil. As more fully described in Mandell, "locating the cornea signalling center from video to retina", j.reflective surgery, v.11, page number 253-.

The point on the cornea where the line of sight intersects the corneal surface is the "optical center" or "center of sight (sight)" of the cornea. It is the primary reference point for refractive surgery because it usually represents the center of the area to be cut in photorefractive keratectomy. Line of sight has traditionally been programmed into laser control systems to govern corneal cutting procedures. However, some surgeons prefer to use the pupillary axis as a reference line. Other surgeons have approximately centered the cutting profile as the corneal vertex, which is generally defined as the area on the cornea with the greatest change in curvature. Experienced practitioners have used various techniques for finding the center of the field of view. In one technique, the angle λ (anglelambda) is used to calculate the position of the center of the field of view relative to the pupil ("light") axis. See the article by Mandell, supra, which includes a detailed discussion of the angles κ and λ, the disclosure of which is incorporated herein by reference in its entirety.

During a LASIK corneal ablation procedure, a portion of the corneal surface is reflected and the exposed surface is ablated. The collected elevation data is used to guide a cutting device, such as a laser, so that the corneal surface can be selectively cut to more closely approximate a spherical surface of appropriate radius about the line of sight, or an "average" ellipse, or a wavefront fingerprint within the cutting zone. Using the line of sight as a reference line for surgery may reduce myopia or otherwise correct pre-operative dysfunctions or visual abnormalities. However, a more irregularly shaped cornea may result, which may exacerbate existing astigmatism or introduce astigmatism or spherical aberration in the treated eye. This would complicate any vision correction measures that need to be taken subsequently. Moreover, any substantial surface irregularity introduced can cause development of scar tissue or local accumulation of tear stains, both of which can adversely affect vision.

The use of the visual line or the pupillary axis as a reference axis for performing the surgical procedure implies the following assumptions: the cornea is symmetric about an axis that extends along a radius of the eye. However, the cornea is an "asymmetric spherical" surface. By "spherical" it is meant that the radius of curvature along any corneal "meridian" is not constant (a "meridian" can be considered to be a curve formed by the intersection of the corneal surface with a plane containing the pupillary axis). In essence, the corneal curvature tends to flatten out gradually from the geometric center to the periphery. By "asymmetric" is meant that the corneal meridians do not exhibit symmetry about their centers. The degree to which the cornea is spherical and/or asymmetric varies from patient to patient or from eye to eye of the same patient.

Analysis of clinical measurements performed according to the surface modeling technique of U.S. patent No.5,807,381 indicates that the point on the corneal surface that is farthest from the reference plane of PARCTS (hereinafter referred to as the "HIGH" point) is a more efficient reference point for corneal ablation and lens design compared to the corneal center or pupil center. Specifically, as shown in patent No.5,807,381, laser ablation about an axis passing through the "high" point produces a much more regularly shaped cornea and removes less corneal material (material) than if the same procedure were performed about an axis near the center of the eye (e.g., the pupillary axis).

Analysis of clinical measurements according to the methods of U.S. Pat. No.5,807,381 and International patent application No. PCT/US03/1763 (published as WO03/101341), the disclosures of which are hereby incorporated by reference in their entirety, has questioned the assumptions that have been made regarding the structure of the human cornea inherent in such well-known corneal analysis techniques as wavefront analysis and astigmatic disc technology (placido disc technology). In particular, it was found that unlike other optical systems, the central portion of the cornea (e.g., extending outward to a 32mm diameter) is not necessarily optically superior to a substantially larger portion of the cornea (e.g., extending outward to a 7mm diameter) in terms of its ability to focus. The central portion of the cornea exhibits a large amount of focused astigmatism. That is, different regions on the cornea are not focused to the same point on the focal axis. In fact, they do not even focus on the same axis. Typically, this difference in focus is most pronounced in the central portion of the cornea, and from the center, the difference in focus actually decreases as the diameter increases.

As disclosed in PCT/US03/1763, vision may be improved by adjusting the focus of the cornea (referred to herein as "orthogonalization") so that different regions are focused to virtually the same axis. This can be done by corneal shaping (e.g., by cutting) or by applying a suitable corrective lens, effectively reducing both radial and axial focal astigmatism. For many patients, an additional benefit of orthogonalization is the substantial reduction of presbyopia (defective myopia). That is, many presbyopic patients who wear orthogonalized contact lenses without components that focus at different distances can achieve both near and distance vision improvement. However, as is common, adequate improvement in both near and distance vision cannot be achieved, and thus, cannot provide full vision improvement for most myopes with aging associated with near vision defects.

The process of achieving laser cutting of the cornea and shaping of a contact lens according to the present invention is illustrated in block diagram form in fig. 1. This process utilizes a cornea image acquisition system (cornealagecapturesystem) 610, a height analysis program (eleventionanalysisprogram) 620, a computer aided design system (computeraideddedsignsystem) 630, a command processor (CommandProcessor)640, and a cornea shaping system (corneasahapingsystem) 650. In conjunction with the elevation analysis program 620, the corneal image capture system 610 generates a three-dimensional topographic (topographic) map of the patient's cornea. The computer aided design system 630 is utilized as an aid in editing or modifying corneal mapping data to create a surface model and data relating to the model is sent to the corneal shaping system 650 via the command processor 640. The command processor 640 uses the mapping data from the computer-aided design system 630 describing the surface of the cornea to be shaped to generate the sequence of command/control signals required by the cornea/lens shaping system 650. The cornea/lens shaping system 650 accepts from the command processor 640 a sequence of commands describing the three-dimensional motion of the cornea/lens shaping system (any coordinate system may be used; for example, cartesian, radial or spherical coordinates) in order to shape the cornea or to shape a machine (e.g., a lathe) for manufacturing a contact lens.

The corneal image acquisition system 610 and the elevation analysis program 620 are preferablyCornea mapping system "System ") that can be derived from the PAR vision system. The height analysis program 620 is a software program executed by a processor (e.g., an IBMTM-compatible PC). Program 620 generates a three-dimensional element (the Z coordinate represents the distance from a reference plane within the eye) for each of a plurality of sample points on the corneal surface as measured by system 610. Each point is defined by its X-Y coordinates mapped into a reference plane and its Z coordinate is determined from the intensity of the point. One way to calculate the height (i.e., Z coordinate) of each point is to compare the X-Y and brightness values measured from the patient's cornea 14 to the coordinates and brightness values of some reference surface of known height (e.g., a sphere of known radius). These reference values may be stored in advance.

The final output of the height analysis program 620 is the X-Y-Z coordinates of a plurality of sample points, commonly referred to as a point cloud (pointcloud), on the surface of the cornea 14. It will be apparent to those skilled in the art that any method capable of producing X, Y, Z corneal data that provides location and elevation information for points on the corneal surface to the required accuracy may be used. In a preferred embodiment, approximately 1200 points are spaced apart from one another in a grid pattern, as viewed in the X-Y plane, so that the projections of the points on the X-Y plane are approximately 200 microns apart from one another.

The X-Y-Z data output from the height analysis program 620 may be formatted in a number of well-known machine-specific (machine-specific) formats. Preferably, the data is formatted in a data exchange file (DXF) format, i.e., an industry standard format commonly used for transferring data between applications. DXF files are ASCII data files that can be read by most computer aided design systems.

Referring now to fig. 2 and 3, a point cloud 100 is depicted (i.e., as projected into the X-Y plane), as would appear when viewing the reference plane along the Z-axis. Each point corresponds to a particular location on the patient's cornea. These data are typically generated from a defined area (working area) of the cornea of approximately 10mm by 10 mm. Thus, there may be as many as 50 rows of data points. The computer-aided design system 630 generates a model (model) or surface 108 (see fig. 4) that matches a topographic map of the patient's corneal surface from the data points produced by the elevation analysis program. In a preferred embodiment, the computer-aided design system 630 is an Anvil5000^TMA program available from manufacturing consulting service (manufacturing consulturationservice) of scottdale (Scottsdale) of Arizona, usa.

Preferably, the cornea matching surface 108 is produced by first generating a plurality of splines 102, wherein each of the plurality of splines 102 is defined by a plurality of data points of the point cloud 100. The generation of splines that intersect multiple data points (i.e., knots) is known per se to those skilled in the art, and once the input data is entered, it may be passed through an navil 5000^TMThe procedure is completed. For more information on the generation of surface models, see U.S. Pat. No.5,807,381, the disclosure of which is incorporated herein by reference. In the preferred embodiment, known non-uniform rational B-spline equations are used to generate the splines, but they may also be generated by other known mathematical equations of splines, such as cubic spline equations or rational uniform B-spline equations. As shown in FIG. 3, in a preferred embodiment, each of the splines 102 lies in a plane parallel to the X and Z axes and includes a row of points from the point cloud 100 in FIG. 3.

A surface 108 is then generated from the splines 102 that matches the corneal surface of the scanned eye. There are many well known mathematical formulas that can be used to generate a surface from a plurality of splines 102. In a preferred embodiment, the well-known nurb (non-uniform rational B of curved surfaces) surface equation is used to generate the corneal surface from splines 102. In this embodiment, the scan area of the eye is approximately 10mmx10mm, thus creating aApproximately 50 splines 102 are built. As shown in fig. 3, a bare (skinned) surface segment 104 is created for a small number (e.g., 5) of adjacent splines. These adjacent bare surface sections 104 share a common boundary spline. Thus, approximately 10 bare surface segments were generated from the point cloud and were generated by Anvil5000 in a manner known to those skilled in the art^TMThe program merges these approximately 10 bare surface sections together to create a composite surface 108.

Neither the original data points nor the knots of splines 102 are necessarily located on surface 108, since the surface is mathematically generated when using the nurb surface equation formula. However, the surface 108 estimates the points within a predetermined tolerance.

A HIGH point (i.e., the point with the greatest Z value) on the generated corneal matching surface 108 is determined. A cylinder 106 of a predetermined diameter is then projected onto the corneal mating surface 108 along an axis parallel to the Z-axis and past the HIGH point. Cylinder 106 preferably has a diameter of about 3mm to about 8mm, typically about 7mm, and the closed contour formed by the intersection of cylinder 106 and surface 108 projects as a ring 106' in the X-Y plane. On the mating surface 108, the contour defines the outer edge 26 of the working area of the cornea. The cornea is most symmetric and spherical about the HIGH point, thus providing the best optical performance at that point.

The outer rim 26 must fit within the (fit) point cloud in order to be able to form the surface of the cornea based on the measured corneal data. The computer-aided design system 630 can then illustrate the default ring 106 '(in the X-Y plane) relative to the point cloud, for example, on a monitor screen, so that the operator can ensure that the ring 106' falls within the point cloud. Further, system 630 can be set up to determine if ring 106 'falls within point cloud 100, and if it does not fall completely within point cloud 100, then alert the user to manipulate the ring (i.e., move the center point of the ring and/or change the radius of the ring) so that ring 106' is located within corneal data point cloud 100. In the worst case, if not enough data is available from the scanned eye, the eye should be rescanned to ensure that the working area of the cornea will fit properly within the point cloud. Alternatively, the area of the point cloud may be made large.

It should be understood that the ring 106' is only a ring when viewed in the X-Y plane (i.e., viewed along the Z-axis). In practice, the outer edge 26 approximates an ellipse and lies in a plane that is inclined relative to the reference plane. The line perpendicular to the tilt plane passing through the HIGH point will be referred to as the "local z-axis" or "tilt axis" and the inclination of the tilt plane relative to the reference plane will be taken as the tilt angle of the corneal working volume.

The cornea is approximately 600 μm thick. In most corneal ablation procedures, a depth of less than 100 μm of the cornea is ablated because there is virtually no risk of scarring by such lasers as are commonly used. Beyond a depth of 100 μm, there is a risk of scar-like defects being left. For example, 120 μm deep cuts are known to cause scarring. However, there is the possibility that the risk of scarring due to surface cutting may be reduced by drug therapy prior to or simultaneously with laser treatment. However, most laser surgery today does not result in scarring, since most procedures are performed under a LASIK scalpel (flap). There is a concern in LASIK that the cut will be too deep with the remaining bed (residual) being less than 250 μm. If the remaining beds are less than this number, structural obstacles may occur. The amplitude of the corneal undulations is typically about 15 to 20 microns from the peak to the valley, and can be as large as 30 microns.

The surgical operations performed according to the invention and the optical lenses manufactured according to the invention will seek to correct the vision of the patient according to the required correction established in the "refraction test". When performing this test, the patient sits in a chair equipped with a special device called a phoropter, through which the patient looks at an eye chart approximately 20 feet away. As the patient looks into the phoropter, the doctor manipulates lenses of different strengths (strength) into view and asks the patient each time whether the patient makes the test chart appear clearer or more blurred through the particular lens placed. In fact, the doctor is able to vary the dioptric power or diopter correction about two orthogonal axes, as well as the degree of rotation of those axes about the Z-axis along the line of sight. The physician continues to modify these three parameters until he reaches optimal vision. The results of the refraction test are generally given in the "a, b, c" table, where "a" is the diopter correction in the first axis, "b" is the additional diopter correction required in the second orthogonal axis, and "c" is the angle of rotation of the first axis relative to the horizontal. The information form is given for each eye and is immediately available for grinding a pair of lenses of the glasses.

A technique for generating a characteristic curve on the surface 108 will now be described, which will be useful in the following. A plane 110 (see fig. 4) is constructed that contains the LOCALZ-axis. The intersection between the plane 110 and the surface 108 defines a first characteristic curve 112. Plane 110 is then rotated, as indicated by line 114, in an increment of 5 deg. in, for example, a counterclockwise direction about the local z-axis, wherein its intersection with surface 108 defines a second characteristic curve 116, represented by the dashed line in fig. 4. This process continues at fixed rotational increments around the local z-axis, for example 5 ° at a time, until the plane 110 sweeps 360 ° to produce a complete set of characteristic curves (meridians), in this case 72 (360 °% 5 °).

Each of these characteristics is then estimated with the best-fit spherical (circular) arc. One way to do this is to simply select a circular arc that passes through three known points of each curve (e.g., the point on which the contour line 106' is in contact, the HIGH point, and the point that is in between these two points when viewed in projection along the local (local) Z-axis). Once the spherical arc is generated, the focus of the portion of the cornea represented by the circular arc can be estimated by the center of the arc. Techniques for locating the center of a spherical arc are well known. The resulting set of arc centers then provides a representation of focus astigmatism.

For illustrative purposes, the previous procedure was performed on a corneal model of a patient with uncorrected visual acuity of 20/15. Figure 5 is a focused astigmatism diagram of a portion of the cornea along the local z-axis extending outward to a diameter of 3.0 mm. In this case, the focus starts at 7.06mm along the LOCALZ-axis and extends an additional 6.91mm outward. FIG. 6 illustrates that the radial divergence within a 3mm diameter is 1.2 mm. Likewise, FIG. 7 illustrates that axial focus astigmatism for a 5mm diameter portion of the cornea begins at 8.99mm and extends an additional 1.69 mm. As shown in figure 8, the radial astigmatism of the same portion of the cornea is 0.49 mm. Figure 9 illustrates that the axial focus astigmatism at 7mm starts at 8.68mm and extends axially an additional 0.47mm, while figure 10 illustrates that the corresponding radial astigmatism is 0.33 mm. It is clear that focus astigmatism is most severe in the central part of the cornea and decreases significantly as the part of the cornea considered is larger. It would therefore be clearly desirable to be able to reduce or eliminate focus astigmatism in at least the central portion of the cornea. This can be achieved by "orthogonalizing" at least a portion of the cornea. Herein, the term "orthogonalizing" refers to reshaping the surface model so that it refocuses the cornea piecewise in the direction of the LOCALZ-axis. The reshaped surface model may then be applied (e.g., by cutting) to the cornea, or the back surface of the contact lens (or another type of optical lens) may be shaped, in order to achieve the desired focus astigmatism correction. It has been found that orthogonalizing the cornea not only reduces radial focus astigmatism, but also substantially reduces axial focus astigmatism, and results in more uniformity in the radius of curvature of the orthogonalized portion of the cornea.

Fig. 11 illustrates the orthogonalization process. This is done for each arc representing a characteristic curve in the manner described below. After the piecewise refocusing, the modified arcs are reassembled into a modified surface model having refocusing characteristics.

In fig. 11, 130 represents one of the semi-meridian arcs corresponding to the characteristic curve. Arc 130 has a center point C whose position has been enlarged to demonstrate a focal point radially spaced from the LOCALZ-axis. Orthogonalization of arc 130 begins by creating a chord (chord)132 between the two ends of the arc. A perpendicular bisector 134 of chord 132 may be constructed and will pass through point C and intersect the LOCALZ-axis at point X. Using the distance from point H (the HIGH point) to point X as the radius, a new arc 130' can now be drawn between the two endpoints of arc 130. Arc 130' will be focused on the local z-axis and will have a larger radius of curvature than arc 130.

In this regard, the arc 130 'may be accepted as the arc defining the modified surface model 108'. However, it would be desirable to avoid too large a change in corneal thickness. Thus, a certain threshold (e.g., 0.0075mm) is defined, and if any portion of arc 130 'is greater than the distance in or out of surface 108, arc 130' is not accepted for use in the modified surface model. However, point x may be moved up or down by half (byhalfthiextceover) on the LOCALZ-axis (depending on the direction in which it is desired to move arc 130'). The arc 130' may then be redrawn and retested against the threshold. This readjustment and detection will continue until an acceptable arc 130' is found. The next arc is then orthogonalized. After all arcs have been orthogonalized, a new surface model 108' is created from all arcs.

As described above, the orthogonalization process may be used in a corneal ablation procedure. Prior to surgery, a corrected corneal surface model is generated that is shaped to reduce macula deterioration (macular degeneration) and provide a refractive correction established by vision testing (as described in the aforementioned patents), and all arcs are orthogonalized. The corrected corneal surface model is then registered (register) with the unmodified corneal surface model and moved toward the unmodified surface until the corrected surface just touches the unmodified surface. If the point of initial contact is in the center of the corrected surface, it moves toward the uncorrected surface until the periphery of the corrected surface just contacts the uncorrected surface at the diameter of the proposed cutting procedure. If the point of initial contact is at the periphery of the corrected surface, it moves toward the uncorrected surface until the center of the corrected surface just touches the uncorrected surface. The corrected surface will then be transferred so that it is at least partially within the cornea, and the cornea is cut until the transferred corrected surface becomes the new surface of the cornea.

The central region of the retina is called the macula (macula), and the very center of the macula, called the fovea (foveola), is the most sensitive. While the macula generally has a diameter in the range of 6 to 7 millimeters, the central foveola generally has a diameter of about 0.35 mm. With perfect orthogonalization, all sub-portions of the cornea are refocused to the center of the macula, i.e., the fovea. When orthogonalizing is performed by refocusing all sub-regions onto the local z-axis, the orthogonalization is not perfect.

According to one aspect of the invention, sub-portions of the cornea may be refocused so as to place their focal points outside the fovea still within the macula, at a controlled lateral distance from the local z-axis. The macula has the shape of a generally spherical cap-shaped segment, and is typically between 6mm and 7mm in diameter and approximately 0.88mm deep.

The difference between the introduced defocus and the off-center focus of the present invention should be noted. Ophthalmologists have long known that distance focusing can be mitigated by defocusing when prescribing corrective lenses, and the benefits of near vision can be obtained. According to the invention, there is no defocus. All sub-portions of the cornea remain fully focused, but the focal point is shifted away from the local z-axis.

Fig. 12 illustrates the concept of off-center orthogonalization. Arc 130 is a sub-portion of the cornea that has an astigmatic focal point X. A normal orthogonalization as shown in fig. 11 would move the focus X to the local z-axis, LZ. Perfect orthogonalization will move it to the foveola F on the macula M. The off-center orthogonalization creates a new arc 130 "'focused at point X' that is a predetermined radius r from the fovea. The axis Z' is parallel to the LOCALZ-axis and passes through point X. For ease of estimation, the macula may be considered flat in the region between axes LZ and Z'.

The preferred way to perform off-center orthogonalization utilizes the technique discussed with respect to fig. 4. Specifically, the anterior surface of the cornea was divided into 72 arcs rotationally spaced by 5 °, and each arc was orthogonalized off-center. The resulting 72 focal spots should be well distributed in the foveal working area W ', wherein the foveal working area W' preferably has a diameter of less than 0.07 mm. Fig. 13 is a top plan view of a fovea showing 72 points P distributed in a spiral pattern on the fovea surface.

A more preferred structure of these points is illustrated in fig. 14. The pattern is formed by polar equationWhere R is the two-dimensional radius of the point from the fovea, a is a constant selected to properly disperse the points throughout the working region M',is the angle of rotation of a particular arc on the cornea. This pattern is preferably helical, since each quadrant of the active area M' has a focal point at the full range of distances from the fovea.

Another preferred pattern is illustrated in fig. 14. In this case, the pattern is made up of two overlapping rose patterns, a large one 150 and a small one 150' offset 45 from the pattern 150. Only one petal of each rose pattern is shown with dots, but it will be understood that each of the other petals is also provided with dots. The dots are evenly distributed between the patterns 150 and 150'. However, the pattern 150 provides the outermost dots and has dots distributed over its outermost two thirds. The pattern 150' provides the innermost dots and distributes them evenly. As a result, the pattern in fig. 14 provides well-distributed dots near or far from the fovea.

It will be appreciated that in all the focus patterns that have been shown, in most cases, the points are equally spaced along the curve. However, those skilled in the art will appreciate that the dots may be provided with unequal spacing so as to be more concentrated in a particular area (e.g., the center or outermost region of the workspace).

In some cases, a further method for off-center orthogonalization has been developed defining further embodiments of the present invention, which is preferred for all of the above embodiments to enhance the overall improvement. This method will be referred to as "offset" off-center orthogonalization. This method is performed exactly as shown in fig. 11, except that once the arc 130' is reshaped, it is tilted clockwise to move point X (the end point of the axis of the arc) to the left in fig. 11 and across the local Z-axis so that it is located at a preselected distance or offset from the local Z-axis. Currently, offset values of less than 0.01mm, preferably approximately 0.0025mm, are contemplated. However, distances in the range of about 0.0025mm to about 0.01mm are still effective.

Fig. 16 illustrates three waveforms that may be used to describe an idealized turtleback shape. Each waveform is a polar plot of curvature (given in diopters) as a function of rotational position. For example, waveform A represents the cornea of an actual patient that is myopic, astigmatic, and exhibits age-related presbyopia. The polar angle is the angle of rotation of a plane containing the local Z-axis (about the tilted local Z-axis) relative to a reference position where the plane intersects the base of the cornea at a position closest to the nose. The curvature is diopters equal to the radius of the arc: the arc, when having a particular rotational orientation, is closest to the semi-meridian arc created by the intersection of the surface of the cornea with the plane. The diopter value is related to the radius of the circular arc by the well-known formula:

337.5 arc radius ═ diopter value

Ideally (to improve vision most comprehensively), waveform a should be shaped to substantially resemble the letter "M", and so is referred to herein as the "M-wave (M-wave)" of the cornea. In this example, it is a somewhat distorted M.

As an initial step in reshaping the cornea to improve vision overall, an idealized M-wave is generated for the cornea. An idealized waveform is generated starting from a polar representation of the patient's cornea (e.g., waveform a) showing the surface curvature along the natural semi-meridian arc of a particular corneal surface. This waveform is independent of waveform a, except that the lowest diopter value in the two waveforms is preferably approximately the same, but waveform B preferably meets some criteria. However, in some cases, improved vision performance can be obtained by making the baseline of 1.5 diopters of waveform B higher than waveform A. First, the peak-to-peak diopter change of the waveform is adjusted to about 3 diopters, preferably about 2.875 diopters. It has been found that if this diopter range is reduced to less than 2 diopters or greater than 4 diopters, there is a significant deterioration in near vision correction. Furthermore, the dip point (dip) D in the M-wave is adjusted so that it is between about 40% and 60% of the peak-to-peak amplitude of the M-wave. Preferably, it is about 50%. The entire waveform is then adjusted to smoothly transition (transition) between the various values. Preferably, when a smooth curve is generated, the peaks occur at about 90 ° and 270 °, and the depression points occur at about 180 °. This produces an ideal M-wave representing the patient's cornea. This wave is represented by the waveform B in fig. 16.

In fact, each lens will have the same M-waveform except for the adjustment made to match the flattest curvature (K value) of the cornea, as determined by, for example, a refractive test, and the necessary distance vision correction. The K value and diopter are typically measured and commonly available to an ophthalmic professional when fitting a lens. To customize the patient's M-wave, it is only necessary to pick up the baseline of the M-wave corresponding to its K value and shift the waveform vertically to provide the diopters necessary to correct distance vision. This defines the lens shape of the patient's custom eyeglasses.

It will be appreciated that waveform B exhibits the flattest surface curvature at 0 ° (the point in waveform B corresponding to the edge of the cornea that will be closest to the nose). Increasing the polar angle, the surface curvature continuously increases until it reaches a maximum at about 90 ° (corresponding to the vertically highest edge of the cornea). The surface curvature then continuously decreases until it reaches a median value at about 180 deg. (corresponding to the edge of the cornea furthest from the nose) and continuously increases to a maximum value at about 270 deg. (corresponding to the vertically lowest edge of the cornea) and continuously decreases until it reaches 0 deg., where the surface curvature returns to its minimum. Thus, the surface described by the M-wave has the idealized turtleback shape discussed above.

In the preceding paragraph, it is assumed that the M-wave of the patient's right eye is being considered. The reference or 0 angle is selected as the point closest to the nose and the polar angle increases counterclockwise. The M-wave for the left eye may be the same (i.e., 0 is at the point furthest from the nose and the polar angle increases clockwise), or it may be a mirror image of the right eye (i.e., 0 is at the nose but the polar angle increases counterclockwise). The former approach would simplify manufacturing and reduce cost since the same lens would be used for both eyes.

In some cases, a better overall improvement in vision will be obtained if an additional adjustment is provided to the surface model represented by waveform B. That is, if an offset is provided, the surface model is orthogonalized off-center by an offset from the local Z-axis of less than about 0.005 mm. The offset is most preferably about 0.0025 mm. An upper offset limit of 0.005mm was chosen because experiments showed that at this value, both distance and near vision deteriorated significantly. As the offset is further increased, distance vision continues to deteriorate significantly.

In one embodiment, the surface model represented by waveform B represents the shape of the posterior surface of a contact lens used by a patient. According to the present invention, the shape of the anterior surface of the lens can be derived by providing the diopter adjustment along waveform B determined to be necessary to correct the patient's distance vision. Typically, this diopter correction will be determined according to conventional refraction testing. At each angle, the anterior surface diopter value Da and radius Ra are determined according to the Zeiss lens formula:

Da＝(-PDp)/(1-(((T/1000)/Na)*Dp))

Ra＝(N_L-N_A)*1000/Da

wherein the content of the first and second substances,

da is the diopter value of the front arc

Dp is the diopter value of the posterior arc

N_LIs the refractive index of the material from which the lens is made

N_AIs the refractive index of air

P is a factor regulating magnification (power)

T is the lens thickness.

After this diopter adjustment, waveform C is generated.

Those skilled in the art will appreciate that the posterior surface of the contact lens need not be shaped as defined by waveform B. In fact, the posterior surface of the contact lens may be any shape calculated to generally conform to the patient's cornea, such as a spherical or ellipsoidal surface. The idealized M-wave is turtle-back shaped, rather than spherical or elliptical, and is universal and independent of the patient's native cornea, except that it preferably has the same minimum curvature as the cornea. Furthermore, the matching to the flattest curvature of the cornea is not relevant for vision correction, but is done to ensure that the lens will be more comfortable.

When the lens is placed on the eye, the lens, the cornea and the tear film therebetween will have substantially the same refractive index. In this way, only the interface between the air and the front surface of the lens will have a considerable impact on vision improvement. The use of the surface shape defined by waveform B for the posterior surface of the lens minimizes unnecessary thickness variations in the lens that may introduce some distortion.

Those skilled in the art will appreciate that the surface model represented by waveform C may also be used to define a desired corneal shape after surgery. Surgery constitutes the actual reshaping of the cornea, while the use of contact lenses constitutes an effective reshaping.

It should be understood that the contact lenses just described above are custom designed contact lenses. However, it is contemplated that M-wave lenses can be provided with pre-prepared prescription forms, as is currently done with mass produced lenses. For example, where the lens has an M-wave posterior surface, the lens can be provided in different base curvature variations or "sizes" (e.g., a larger base curve for a relatively flat cornea, a medium base curve for a cornea of medium or average curvature, and a smaller base curve for a more steeply shaped cornea). In all cases, the M-wave has the idealized shape described above, so the only difference between the dimensions is the actual value of the initial curvature. Each posterior curve set will include a lens subset having a different anterior curve, so that each size will include a lens subset having the necessary diopter adjustment for correcting a different distance of refractive error. The patient will only require two optometry tests in order to get a corrective prescription. First, the optometrist will perform a conventional refraction test to determine the diopter correction required for distance vision. Then, during the initial visit, the optometrist or lens fitter may also perform a conventional keratometer test, which produces diopter readings for the flattest and steepest portions of the cornea. The flattest curvature of the keratometer test determines whether the patient requires a lens with a small, medium or large back surface base curve (for optimal comfort), and the refractive test also establishes the required distance correction. Given this prescription, the eye professional will easily configure the patient with the most appropriate M-wave lens that will provide overall vision improvement.

Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various additions, modifications and substitutions are possible, without departing from the scope and spirit of the invention. For example, the invention is applicable not only to corneal incisions and contact lenses, but also to any other type of lens, including cataractous, phakic, intraocular, intracorneal, and spectacle lenses.

Claims (8)

1. A method for generating a desired surface model of a cornea of an eye with the aid of a computer program for generating a surface model of a cornea, comprising the steps of: on a surface model of a cornea of an eye, focal points at different positions on the surface model are determined, and a shape of the surface model is modified so as to move the focal points to predetermined positions relative to a predetermined reference axis without forcing them to move to a common axis, the modified model representing a desired surface model.

2. The method of claim 1, wherein the reference axis passes through a HIGH point.

3. The method of claim 1, wherein the reference axis is a LOCALZ-axis.

4. The method of claim 1, wherein the surface model of the cornea closely represents at least a portion of the surface of the cornea in three-dimensional space as a smooth, freeform surface, the modifying step comprising changing the shape of at least a portion of the surface model to produce a modified surface model.

5. The method of claim 1, wherein the shape is modified such that multiple focal points are offset to form a predetermined pattern on the retina of the eye.

6. The method of claim 5, wherein the predetermined pattern is one of a ring, a spiral, a rose pattern, and a double rose pattern.

7. An optical lens having an anterior surface, a posterior surface and an optical center on its anterior surface, the anterior surface having an M-wave shape such that the surface curvature measured along a curve passing through the optical center varies substantially as a smoothed letter M with respect to an angular direction about the optical center, wherein the 0 ° angular direction is substantially the point closest to the nose when the lens is worn and the central foveal point of the M occurs substantially at the point farthest from the nose when the lens is worn, corresponding to the 180 ° direction, the maximum values of the M occurring substantially at the vertically highest and lowest ends of the lens when the lens is worn, corresponding to the 90 ° and 270 ° directions, respectively,

wherein a curve on the anterior surface of the lens passing through the optical center defines focal zones on the anterior surface corresponding to different locations on a corneal surface of the eye, each focal zone shaped to move the focus of the corresponding location of the cornea to a predetermined position relative to a predetermined reference axis in the eye without forcing the focus of each zone to a common point.

8. A method of determining a required shape change to a cornea of an eye, the method being performed with the aid of a computer system comprising a display device, the method comprising the steps of:

modeling an anterior corneal surface as a surface model tailored to an M-wave shape such that surface curvature measured along a curve passing through an optical center varies substantially as a smoothed letter M in relation to an angular direction about the optical center, wherein the 0 ° angular direction is substantially the point closest to the nose when the lens is worn and the M's central foveal point occurs substantially at the point farthest from the nose when the lens is worn corresponding to a 180 ° direction, the M's maximum value occurs substantially at the vertically highest and lowest ends of the lens when the lens is worn corresponding to 90 ° and 270 ° directions, respectively;

viewing the surface model on the display device:

generating a first signal configured to control another apparatus to shape a contact lens so that an anterior surface of the lens has the M-wave shape; or

Generating a second signal configured to control a device according to the M-wave shape,

wherein said curve modeling said front surface and passing through said optical center defines different focal regions, said method further comprising the steps of:

in the modeling step the focal points of the different focal zones are determined and the model formed by the modeling step is modified such that the focal points are moved to predetermined positions relative to a predetermined reference axis without forcing them to move to a common point, the modified model representing a desired reconstruction of the cornea.