DEVICE AND METHOD FOR THE AMELIORATION OF ECTATIC AND IRREGULAR CORNEAL DISORDERS

Abstract

Devices and methods for the amelioration of ectatic corneal disorders using corneal augmentations derived from corneal tissue are disclosed. The shape of the augmentation is determined using data obtained from mapping of a patient's cornea based on computerized corneal topography and tomography. Factors considered include the maximum keratometry and specific iso-deviation contours. In one embodiment, an augmentation is a corneal inlay, intended for insertion into an intrastromal pocket. In a further embodiment, the augmentation is a corneal onlay, intended to be positioned over a region of the cornea from which the epithelial layer has been removed. The corneal onlay is held in place until the epithelial layer regrows over the augmentation. In a further embodiment, the inlay or onlay augmentation is followed by a post-augmentation, further reshaping of the corneal augmentation. In one embodiment, this further reshaping is photorefractive keratectomy (PRK) surgery.

Claims

1-21. (canceled)

22. A method for amelioration of an abnormality of a cornea, the method comprising: determining a severity of the abnormality of the cornea; creating a corneal map of the cornea quantifying a deviation of the abnormality from an optimal corneal shape; calculating, using the corneal map and the severity, a three-dimensional shape of a corneal augmentation to ameliorate the abnormality of the cornea; producing the corneal augmentation with the three-dimensional shape; and augmenting the cornea with the corneal augmentation.

23. The method of claim 22, wherein producing the corneal augmentation comprises obtaining a corneal template from a source other than the cornea being treated, wherein the corneal template is one of a corneal autograft, corneal allograft, a corneal xenograft, and a manufactured corneal tissue.

24. The method of claim 22, wherein the abnormality is keratoconus, the severity is measured by a maximum keratometry (K-max), and the corneal map is obtained using corneal tomography or corneal topography.

25. The method of claim 24, wherein a maximum thickness of the corneal augmentation is proportional to the maximum keratometry of the keratoconus and is determined by the equation: t=10?K-max?300, where t represents the maximum thickness in ?m, and K-max represents the maximum keratometry measured in diopters.

26. The method of claim 22, wherein the three-dimensional shape is a sector cut from a doughnut shape.

27. The method of claim 26, wherein the sector cut from the doughnut shape has an inner radius of about 3 mm to about 5 mm and an outer radius of about 7 mm to about 9 mm.

28. The method of claim 27, wherein the sector cut from the doughnut shape has a uniform thickness determined using the equation: t=10?K-max?300, where t is thickness in ?m, and K-max is maximum keratometry measured in diopters.

29. The method of claim 22, wherein the corneal map is an elevation map and the three-dimensional shape has a plan projection that is one of a curve, a polygon, a lenticule, a doughnut, a crescent or an arc.

30. The method of claim 29, wherein the plan projection is at least in part a best fit to an iso-elevation line of the elevation map.

31. The method of claim 22, wherein producing the three-dimensional shape comprises generating, using a processor, a cutting file based on the corneal map and the severity, wherein the cutting file contains instructions to form the corneal augmentation using a femtosecond laser.

32. The method of claim 22, wherein the corneal augmentation is an inlay and augmenting the cornea further comprises creating an intra-stromal cavity using a femtosecond laser, wherein the intra-stromal cavity is sized and shaped to accommodate the inlay.

33. The method of claim 22, wherein the corneal augmentation is an onlay placed external to the cornea being treated and augmenting the cornea further comprises removing, using a femtosecond laser, a contiguous region of epithelial tissue corresponding in area to a plan projection of the corneal augmentation.

34. The method of claim 33, wherein augmenting the cornea further comprises retaining the onlay on the cornea using a surface chamfer of epithelial tissue on a periphery of the removed contiguous region of epithelial region.

35. The method of claim 22, the method further comprising after augmentation, reshaping the cornea with photorefractive keratectomy (PRK) surgery using an excimer laser.

36. A device for amelioration of an abnormality of a cornea, the device comprising: a corneal augmentation having a three-dimensional shape, wherein the three-dimensional shape has a plan projection that is one of a curve, a polygon, a lenticule, a doughnut, a crescent, or an arc, and wherein the plan projection is at least in part a best fit to an iso-elevation line of an elevation map.

37. The device of claim 36, wherein the three-dimensional shape is a sector cut from a doughnut shape having an inner radius of about 3 mm to about 5 mm and an outer radius of about 7 mm to about 9 mm.

38. The device of claim 37, wherein the three-dimensional shape has a uniform thickness determined using the equation: t=10?K-max?300, where t is thickness in ?m, and K-max is maximum keratometry measured in diopters.

39. The device of claim 36, wherein the three-dimensional shape is determined by a method comprising: determining a measure of severity of the abnormality of the cornea; creating a corneal map of the cornea quantifying a deviation of the abnormality from an optimal corneal shape; and calculating, using the corneal map and the measure of severity, the three-dimensional shape of the corneal augmentation to ameliorate the abnormality of the cornea.

40. A system for amelioration of an abnormality of a cornea, the system comprising: at least one processor configured to: generate a corneal map of a patient indicating a measure of severity of the abnormality and a deviation between the abnormality and an optimal corneal shape; calculate, using the corneal map, a three-dimensional shape of a corneal augmentation to ameliorate the abnormality of the cornea; and cause a laser and a moveable stage to produce the corneal augmentation having the three-dimensional shape.

41. The system of claim 40, wherein the corneal map is an elevation map and the three-dimensional shape has a plan projection that is one of a curve, a polygon, a lenticule, a doughnut, a crescent or an arc, and wherein the plan projection is at least in part a best fit to an iso-elevation line of the elevation map.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0017] FIG. 1A shows a schematic cross-section of a normally functioning human eye.

[0018] FIG. 1B shows a schematic cross-section of a human eye exhibiting an abnormality of the cornea.

[0019] FIG. 2A shows a schematic cross-section of a cornea having two intra-stromal cavities in preparation for having corneal augmentations as inlays.

[0020] FIG. 2B shows a schematic cross-section of a cornea having two intra-stromal cavities.

[0021] FIG. 2C shows a schematic cross-section of a cornea having two intra-stromal corneal augmentations as inlays.

[0022] FIG. 3A shows a schematic cross-section of a cornea exhibiting keratoconus.

[0023] FIG. 3B shows a schematic cross-section of a cornea prepared to receive a corneal augmentation as an onlay.

[0024] FIG. 3C shows a schematic cross-section of a cornea augmented with a corneal augmentation as an onlay.

[0025] FIG. 3D shows a schematic cross-section of a cornea augmented with a corneal onlay after regrowth of the epithelial tissue.

[0026] FIG. 4 shows a schematic plan view of a human eye.

[0027] FIG. 5A shows a plan view of a doughnut shaped corneal template.

[0028] FIG. 5B shows a plan view of two segments cut from a doughnut shaped corneal template.

[0029] FIG. 5C shows a cross-sectional view of a segment cut from a doughnut shaped corneal template.

[0030] FIG. 6A shows a plan view of a tangential map of a cornea exhibiting keratoconus.

[0031] FIG. 6B shows a schematic plan view of doughnut segment corneal augmentations located relative to a tangential map of a cornea exhibiting keratoconus.

[0032] FIG. 7A shows schematic rendering of an elevation map of a cornea exhibiting keratoconus.

[0033] FIG. 7B shows a schematic cross-section showing a surface of a cornea exhibiting keratoconus and a best fit sphere as a reference.

[0034] FIG. 7C shows a schematic cross-section showing a surface of a cornea exhibiting keratoconus and an enhanced best fit sphere as a reference.

[0035] FIG. 8A shows a schematic representation of an iris image superimposed on an elevation map.

[0036] FIG. 8B shows a schematic representation of an elevation map showing a keratoconus circle and a 3-mm representation of a pupil.

[0037] FIG. 9 shows a schematic representation of a corneal augmentation shaped to have a plan projection matching an iso-elevation line.

[0038] FIG. 10A shows a schematic plan view of one embodiment of a corneal augmentation.

[0039] FIG. 10B shows a schematic cross-sectional view of one embodiment of a corneal augmentation.

[0040] FIG. 11 shows a schematic plan view of a corneal augmentation shaped to avoid covering the pupil.

[0041] FIG. 12 shows a schematic plan view of a corneal augmentation having a doughnut shape to avoid covering the pupil.

[0042] FIG. 13 shows a flow diagram showing representative steps in the automated determination of a three-dimensional shape of a corneal augmentation.

[0043] FIG. 14 shows a flow diagram showing representative steps in the automated fabrication of a corneal augmentation.

BEST MODE FOR CARRYING OUT THE INVENTION

[0044] FIG. 1A shows a schematic cross-section 101 of a normally functioning human eye.

[0045] In a normally functioning human eye, an incoming, parallel beam of light 110 may be light correctly focused 111 onto the retina 108 by the combined action of a lens 107 and a cornea 105. The image created on the retina 108 may then be transmitted to the brain via the optic nerve 109. The anterior cavity 106 is typically filled with a clear fluid, the aqueous humor, and separates the cornea 105 from the lens 107.

[0046] FIG. 1B shows a schematic cross-section 102 of a human eye exhibiting an abnormality of the cornea that may be an ectatic disorder.

[0047] Corneal ectasia may be caused by the thinning and subsequent distortion of the cornea and may be manifested as a condition such as, but not limited to, keratoconus, pellucid marginal degeneration and keratoglobus. As a consequence of the thinning, the cornea 112 exhibiting an ectatic disorder may be distorted away from the normal spheroidal shape of a healthy cornea, thereby impairing its optical performance. For instance, only a small fraction of an incoming, parallel beam of light 110 may be correctly focused on the retina 108, while the remainder of the light 113 may not brought to a correct focus on the retina.

[0048] FIG. 2A shows a schematic cross-section of a cornea exhibiting an ectatic disorder.

[0049] As shown, the cornea may be exhibiting keratoconus 209 in which a portion of the cornea may assume an irregular optical surface that may sometimes be referred to as a cone.

[0050] The degree or severity of the keratoconus 209 may be characterized by the deviation of the cornea from an optimal optical structure. Such an optimal optical structure may, for instance, be an ideal cornea, i.e., a portion of spheroid having a refractive power in the range of 30 to 50 diopters with an eccentricity ranging from ?2 to +2. The severity of the condition may be quantified by a number of clinical variables. These variables may, for instance, include the following: [0051] 1: The maximum keratometry or K-max. This may be measured as the maximum deviation of the cornea from the ideal and may determine the severity of the keratoconus. A measure of the maximum keratometry 210 may, for instance, be obtained using an instrument such as, but not limited to, a Pentacam? manufactured by OCULUS Optikger?te GmbH in Wetzlar, Germany. The measurement may be quantified in diopters or as a deviation in ?m of the anterior surface of the cornea 211 from a best fit sphere 207 for the anterior surface of cornea, or as a deviation in ?m of the posterior surface of the cornea 212 from a best fit sphere 208 for posterior surface of cornea, or a combination thereof. [0052] 2: An estimate of the corneal curvature over the visual axis. This may be obtained from refraction measurements of the degree of myopia and hyperopia caused by the deformed cornea. The myopia may be measured assuming the visual axis passes through the steepest part of the deformed cornea, i.e., the cone of the keratoconus. The hyperopia may be measured by assuming the visual axis passes through the flatter part of the deformed cornea. Both of this refraction measurements may also be calculated from data obtained using corneal tomography or topography as performed by an instrument such as, but not limited to, the aforementioned Pentacam?. [0053] 3: The location of the so-called cone of the keratoconus, particularly the location of the cone relative to the pupil. This clinical location may be obtained by overlying a map of the cornea with an iris image. A map of the cornea may show the local focusing power of the cornea and may be obtained with an instrument such as, but not limited to, a Pentacam?. Optical topography and tomography instruments such as the Pentacam? typically have an iris camera that may provide a suitable iris image. [0054] 4: The diameter of the cone on the cornea. This may, for instance, be obtained from an elevation map that may compare the local height of the cornea to a reference surface such as, but not limited to, a best fit sphere. For instance, a best fit sphere 207 for the anterior surface of the cornea may be compared to the anterior surface of the cornea 211 to produce an elevation map. A roughly circular patch may then become apparent as the boundary at which the cornea starts to deviate significantly from the best fit sphere. The diameter of a best fit circle to this region may then be deemed to be the diameter of the cone. The same calculation may be done comparing the posterior surface of the cornea 212 to a best fit sphere 208 for the posterior surface of the cornea.

[0055] Based on the clinical measurements of the severity, location and diameter of the keratoconus cone, a clinician may then determine both a best device, or corneal augmentation, and a best course of treatment. The device may be either a corneal inlay or a corneal onlay and the treatment may, for instance, be a multistep treatment in which a corneal inlay or onlay is added to the patent's cornea, followed later by laser reshaping of the thickened cornea.

[0056] FIG. 2B shows a schematic cross-section 202 of a cornea having two intra-stromal cavities in preparation for having corneal augmentations as inlays.

[0057] Depending on factors such as, but not limited to, the severity and location of the disorder, a clinician may opt to treat it with a single inlay, or with multiple inlays.

[0058] The intra-stromal cavities 213 and 214 may be created in the corneal stroma 205 using any suitable surgical means though the use of a femtosecond laser may be preferred as the photodissociation incisions produced by a femtosecond laser cause minimal damage to surrounding tissue. The intra-stromal cavities 213 and 214, or pockets, may create a space appropriately sized and shaped to each receive a corneal augmentation. A typical cornea is about 540 ?m +/?30 ?m thick though, with ectasia, the thickness in regions may be as little as 300 ?m. An optimal depth for locating the intra-stromal cavities may be between 90 ?m from the epithelial tissue and at least 100 ?m above the posterior surface of the cornea, or Descemet's layer. Preferably, the location may be as close to the 90 ?m limit as possible. There may be entrances to the intra-stromal cavities 213 and 214 that pierce the epithelial tissue 206 and allow for the insertion of the corneal augmentations.

[0059] FIG. 2C shows a schematic cross-section 202 of a cornea having two intra-stromal corneal augmentations 216 and 218 that may be corneal inlays.

[0060] The corneal augmentations 216 and 218 may have been placed, or inlayed, into the intra-stromal cavities 213 and 214 thereby ameliorating the keratoconus by strengthening and reshaping the cornea. In particular, both the anterior surface of the cornea 211 and the posterior surface of the cornea 212 may now more closely aligned to the best fit sphere 207 for anterior surface of cornea and the best fit sphere 208 for posterior surface of cornea respectively. The cornea may now more closely approximates an ideal optical structure, thereby improving its optical performance and the patient's vision.

[0061] FIG. 3A shows a schematic cross-section 301 of a cornea exhibiting keratoconus.

[0062] As in FIG. 2A, the cornea may be exhibiting keratoconus 209 having a maximum keratometry 210 in a vicinity of the thinnest part of the corneal stroma 205. The deformation of the cornea may be measured as a deviation of the anterior surface of the cornea 211 from a best fit sphere 207 for anterior surface of cornea. An almost identical pattern may be seen in the deviation of the posterior surface of the cornea 212 from a best fit sphere 208 for posterior surface of cornea. Both these deviations may be mapped and visualized as elevation maps by means of tomography or topography using an instrument such as, but not limited to, the Pentacam? mentioned above.

[0063] FIG. 3B shows a schematic cross-section 302 of a cornea prepared to receive two corneal augmentations as corneal onlays. A first surgical step in the onlay procedure may be to remove one or more regions 305 and 310 of epithelial tissue 206. This removal may be performed by any suitable surgical procedure, but the use of a femtosecond laser may be preferred as the photodissociation incisions produced by a femtosecond laser cause minimal damage to surrounding tissue. The regions 305 and 310 in which epithelial tissue is removed may typically be on either side of the thinnest part of the corneal stroma 205.

[0064] In addition to removing the epithelial tissue, a surface chamfer 306 may be produce on a periphery of the region of removed epithelial tissue. This may also be done using a femtosecond laser and may serve to help secure the on-laid corneal augmentation.

[0065] FIG. 3C shows a schematic cross-section 303 of a cornea augmented with two corneal augmentations 308 and 311 that may be corneal onlays.

[0066] The corneal augmentations 308 and 311 may be corneal onlays that may be placed over, or on-laid, over the regions in which epithelial tissue has been removed. The corneal augmentations may be held in place temporarily by having its outer periphery tucked under a surface chamfer 306 on the periphery of the region of removed epithelial tissue. The corneal augmentation may also or instead be temporarily held in place by surgical glue or sutures, or a combination thereof.

[0067] FIG. 3D shows a schematic cross-section 304 of a cornea augmented with two corneal onlays after regrowth of the epithelial tissue 309.

[0068] Regrowth of the epithelial tissue may take approximately a few days to a week. During this period a patient may wear surgical contact lenses to protect the augmentation. As the epithelial tissue regrows, the corneal augmentations 308 may integrate with the corneal stroma 205 thereby strengthening and reshaping the cornea. In particular, both the anterior surface of the cornea 211 and the posterior surface of the cornea 212 may now be more closely aligned to the best fit sphere 207 for anterior surface of cornea and the best fit sphere 208 for posterior surface of cornea respectively. The cornea may now more closely approximate an ideal optical structure, thereby ameliorating the keratoconus. This may also improve the cornea's optical performance and the patient's vision.

[0069] Although the procedures detailed in FIGS. 2A-C and 3A-D, are shown as having two corneal augmentations each, there are many occasions on which a single suitably shaped and placed corneal augmentation may prove as, or even more, effective in ameliorating the corneal abnormality.

[0070] The procedures detailed in FIGS. 2A-C and 3A-D, i.e., augmentation with corneal inlays and corneal onlays, may themselves be sufficient to ameliorate the abnormality, or ectatic corneal disorder. However, they may also or instead be a first step, and may be followed by a post-augmentation further shaping of the corneal augmentation. The post-augmentation further shaping of the corneal augmentation may, for instance, be a surgery such as, but not limited to, a photorefractive keratectomy (PRK) surgery or a phototherapeutic keratectomy (PTK). Such surgeries may, for instance, be accomplished using a suitable laser such as, but not limited to, a femtosecond laser, or an Excimer laser, or a combination thereof.

[0071] FIG. 4 shows a schematic plan view 401 of a human eye. As shown, the eye typically consists of an eyeball 407 contained within a protective socket and surrounded by eyelashes 408. Components of the eye that participate in the imaging function of the eye include the iris 406 and the pupil 405. The pupil 405, for instance, is a variable aperture through which light rays pass to be imaged onto the retina at the rear of the eye.

[0072] FIG. 5A shows a plan view 501 of a doughnut shaped corneal template.

[0073] The initial corneal template, before being shaped into a doughnut, may have been obtained as any suitable material such as, but not limited to, as a corneal autograft, a corneal allograft, a corneal xenograft, a manufactured corneal tissue, or some combination thereof. In a preferred embodiment, the corneal template may be obtained from a donated human cornea, as prepared, and or preserved, by, for instance, a reputable eye bank such as, but not limited to, CorneaGen Inc., headquartered in Seattle, WA, which is a subsidiary of SightLife, Inc, also headquartered in Seattle, WA.

[0074] Such eye banks typically treat the corneal template for multiple purposes, such as but not limited to: [0075] improve the biocompatibility of the corneal template by decellularization; [0076] aid in preserving the corneal template by decontamination and sterilization; [0077] maintain the clarity of the corneal template and minimize edmea by deturgessing agents; [0078] increase the biomechanical strength of the corneal template by the addition of stiffening agents; [0079] improve the case of performing the augmentation procedure by marking for orientation, and by suitable dying for visibility; [0080] allow the corneal template and the corneal augmentation obtained from it to be kept at room temperature for reasonable lengths of time, typically up to two years, and, [0081] improve postoperative healing and prophylaxis by soaking in drugs, biologics, or regenerative therapies.

[0082] The initial corneal template may then be shaped into a doughnut, or ring shape, having a circular outer radius 505 and a circular inner radius 506. This shaping may, for instance, be done using a femtosecond laser or an Excimer laser. The doughnut, or ring shape, may have one or more lateral cuts 507 that may also be accomplished using a femtosecond laser. These lateral cuts may result in corneal segments having a required arc length 508.

[0083] The outer radius 505 may, for instance, be in a range of 7 to 9 mm, and is more preferably about 8 mm. The inner radius 506 of a doughnut shaped corneal template may be in a range of 3 to 5 mm and is more preferably about 4 mm.

[0084] FIG. 5B shows a plan view 502 of two segments 509 and 510 cut from a doughnut shaped corneal template. Once trimmed to an appropriate thickness, these segments may then be suitable corneal augmentations. They may be used singly or in combination. Although FIG. 5B shows two segments being cut from the doughnut, a single arc shaped segment having an arc length of greater than 180 degrees may instead be obtained from the doughnut.

[0085] FIG. 5C shows a cross-sectional view 503 of a segment cut from a doughnut shaped corneal template. Once trimmed to an appropriate thickness, this segment may then be a suitable corneal augmentation.

[0086] A typical width 512 of a doughnut sector shaped corneal augmentation may be in a range of 3 to 5 mm and is more preferably about 4 mm.

[0087] A thickness 511 of a doughnut sector shaped corneal augmentation may depend on a severity of the corneal abnormality. The thickness 511 of the corneal augmentation may, for instance, be proportional to the maximum keratometry, a.k.a. the K-max, of the abnormality.

[0088] For instance, a satisfactory relationship between maximum thickness of the corneal augmentation and K-max has been determined through experience to be that represented in Table 1.

TABLE-US-00001 TABLE 1 Maximum thickness of collagen augmentation in ?m verses maximum keratometry measured in Diopters Tissue Thicknees Maximum Keratometry (um) (Diopters) 100-200 45-50 200-250 50-55 250-300 55-60 300-350 60-65 350-400 65-70 400-450 70-75 450-500 >75

[0089] The values in Table 1 may be approximated by the equation:

[00001]$\begin{array}{cc}t=10?K-\max -300& \left(1\right)\end{array}$ [0090] where t represents the maximum thickness in ?m, and K-max represents the maximum keratometry in diopters.

[0091] FIG. 6A shows a plan view 601 of a tangential map of a cornea exhibiting keratoconus.

[0092] Data obtained in examining an eye using tomographic or topographic systems such as, but not limited to, a Pentacam? may be displayed in a number of ways including, but not limited to, pachymetric maps that display the corneal thickness, axial and tangential maps that display local curvature of the cornea, and elevation maps that display the corneal surfaces with respect to a reference surface.

[0093] A tangential map is typically displayed in false color, with particular colors representing specific local powers of refraction. For instance, a iso-diopter line 605 of elevated power may be displayed in a warmer color tending to the red end of the spectrum, while a iso-diopter line 606 of diminished power may displayed in colder color tending to the blue end of the spectrum. A maximum keratometry 210 may, therefore, be displayed as a dark red. A typical tangential map may fill the circumference 607 of the cornea and be overlaid with a 3-mm circle 608 representative of the pupil of the eye.

[0094] FIG. 6B shows a schematic plan view 602 of two doughnut segment corneal augmentations located relative to a tangential map of a cornea exhibiting keratoconus.

[0095] As shown in FIG. 6B, a first corneal augmentation 609 may be located on one side of the maximum keratometry 210. The first corneal augmentation 609 may further be located so that an outer edge is, in part, a best fit to a first iso-diopter line 610 of elevated power, while an inner edge may be a best fit to a second iso-diopter line 611 of elevated power. The arc length of the first corneal augmentation 609 may also be constrained by the iso-power lines.

[0096] A second corneal augmentation 612, if deemed necessary for amelioration of the corneal disorder, may be located on the other side of the maximum keratometry 210. The second corneal augmentation 612 may further be located such that an outer edge may be, in part, a best fit to a first iso-diopter line 613 of diminished power, while an inner edge may be, in part, a best fit to a second iso-diopter line 614 of diminished power. The arc length of the second corneal augmentation 609 may also be constrained by the iso-power lines.

[0097] FIG. 7A shows schematic rendering of an elevation map 701 of a cornea exhibiting keratoconus.

[0098] Data obtained in examining an eye using tomographic or topographic systems such as, but not limited to, a Pentacam? may be displayed in a number of ways including, but not limited to, pachymetric maps that display the corneal thickness, axial and tangential maps that display local curvature of the cornea, and elevation maps that display the corneal surfaces with respect to a reference surface.

[0099] An elevation map is typically displayed in false color, with particular colors representing particular amounts of deviation of the corneal surface from a reference surface. In order to conform to patent office drawing requirements, the elevation map 701 has been shown with dotted lines representing iso-elevation lines, i.e., lines that would normally be displayed as a particular color. For instance, iso-elevation line 706 represents a particular amount of elevation of a corneal surface above a reference surface and would, by convention, normally be displayed by a warm color tending to the red end of the spectrum. The iso-elevation line 707 represents an elevation of a corneal surface below a reference surface and would normally be displayed by a cold color tending to the blue end of the spectrum. A zero iso-elevation line 705 would normally be displayed as a color in the yellow to green part of the spectrum.

[0100] The numbers 0, 90, 180 and 270 represent orientation in degrees as per ophthalmic convention.

[0101] FIG. 7B shows a schematic cross-section 502 showing a surface of a cornea exhibiting keratoconus 710 and a best fit sphere 709 as a reference.

[0102] The cross-section 702 is taken on the line BB in FIG. 7A. The best fit sphere 709 is the best fit sphere to the entire corneal surface 708 that may include data points from the region of keratoconus 710. The elevation map shown in FIG. 7A may represent the difference between the best fit sphere 709 and one of the surfaces of the cornea. As a point of reference, in normal eyes the anterior elevations are typically in a range 1.63+/?1.4 ?m. In a patient with keratoconus, the anterior elevations may be the range of 20.9+/?21.9 ?m. Best fit spheres typically have a radius in a range of 6.5+/?2 mm.

[0103] FIG. 7C shows a schematic cross-section 703 showing a surface of a cornea exhibiting keratoconus 710 and an enhanced best fit sphere 711 as a reference surface.

[0104] The enhanced best fit sphere 711 may be calculated using data from the corneal surface 708 but excluding data from the region 712 that may represent the region most affected by the keratoconus 710.

[0105] FIG. 8A shows a schematic representation 801 of an iris image 406 superimposed on an elevation map.

[0106] By having the image of the iris 406 superimposed on the elevation map, it may be possible to determine the relative position of the pupil 405 and a circle 806 defining a diameter of a keratoconus. Also shown are the other iso-elevation lines 805.

[0107] FIG. 8B shows a schematic representation 802 of an elevation map having iso-elevation lines 805. Also shown are a keratoconus circle 806 and a 3 mm circle 807 that may represent the position of the pupil. The circle 806 defining a diameter of a keratoconus may, for instance, be a best fit circle to the iso-elevation line at which the surface of the cornea starts to deviate significantly from the best fit sphere. The diameter of a best fit circle may be deemed to be the diameter of the cone of the keratoconus.

[0108] Also shown is a vector 810 representing a distance and direction between the center of the pupil and the center 808 of the keratoconus maximum.

[0109] FIG. 9 shows a schematic representation 901 of a corneal augmentation 905 shaped to have a plan projection matching an iso-elevation line 805 of an elevation map of a cornea. The corneal augmentation 905 may be roughly centered over the keratoconus maximum 808.

[0110] The selection of an appropriate iso-elevation line may define the peripheral shape of a plan projection of the corneal augmentation 905 and its maximum thickness may be determined by the severity of the keratoconus as measured by the value of the keratoconus maximum, a.k.a. K-max.

[0111] For instance, a satisfactory relationship between maximum thickness of the corneal augmentation and K-max has been found through experience to be that represented in Table 1 shown above, and may be approximated by Equation 1, shown above.

[0112] FIG. 10A shows a schematic plan view 1001 of a corneal augmentation 905.

[0113] Although the corneal augmentation 905 shown in the figure has a plan projection matching an iso-elevation line of an elevation map of a cornea, one of ordinary skill in the art may appreciate that the plan projection may be any suitable plan projection such as, but not limited to, a polygon that may be a best fit, in part, to the iso-elevation line, a lenticule that may be a best fit, in part, to the iso-elevation line, a circle that may be a best fit, in part, to the iso-elevation line, a free-form curve that may be a best fit, in part, to the iso-elevation line, a crescent shape may be a best fit, in part, to the iso-elevation line, or some combination thereof.

[0114] The corneal augmentation 905 may have been created from a corneal template that may then have been transformed into to the appropriate three-dimensional shape using any suitable material removal or cutting techniques such as, but not limited to, a computer guided femtosecond laser, or a computer guided Excimer laser, or some combination thereof.

[0115] The corneal template may have been obtained as any suitable material as discussed in more detail previously.

[0116] FIG. 10A also shows the corneal augmentation 905 marked with placement indicia. The indicia may for instance be small holes punched in the corneal augmentation and arranged to provide both positioning and orientation information. For instance, a first placement indicium 1005 marking a 90-degree alignment may have three small holes that indicate placement vertically up. A second placement indicum 1006 marking a 270-degree alignment may have only a single hole, that indicates placement vertically down. When an imaginary line is drawn from first indicium to the second, the line may pass through the center of the 3 mm diameter 807 circle representing a pupil. In actual placement, when correctly placed, the imaginary line may pass through the center of the patient's pupil. Similarly, a third placement indicium 1008 marking a 180-degree alignment may have two holes, while a fourth placement indicium 1007 marking a 0-degree alignment that may have a single hole. When an imaginary line is draw from the third to the fourth placement indicium to it may pass horizontally thorough the center of the pupil when the augmentation is correctly positioned and oriented.

[0117] One of ordinary skill in the art may appreciate that although the placement indicia have been described in terms of punched holes any suitable marking system may be used including, but are not limited to, colored dyes, small incisions, or some combination thereof.

[0118] FIG. 10B shows a schematic cross-sectional view 1002 of a corneal augmentation 905. As shown, the corneal augmentation 905 has a crescent shaped cross-section with a maximum thickness 1009 that may be proportional to the maximum keratometry, or K-max, and may be determined by Equation 1, or Table 1. If the corneal augmentation 905 is intended for use as an onlay, the posterior surface 1010 may be shaped to be a match to the anterior surface of the cornea in the region where the onlay augmentation is intended to be placed.

[0119] Although the augmentation cross-section is shown as a crescent shape, one of ordinary skill in the art may realize that it may be of any suitable shape such as, but not limited to, a rectangle, an oval, a sphere, a portion of a sphere, or some combination thereof.

[0120] FIG. 11 shows a schematic plan view 1101 of a corneal augmentation 1105 shaped to avoid covering the pupil.

[0121] The plan projection of the corneal augmentation 1105 shaped to avoid covering the pupil may have a portion 1106 of the periphery that may be fitted to an iso-elevation line 805, and a portion 1107 of the periphery to a 3-mm diameter 807 circle representing a position of a pupil. A reason for making such an augmentation may be to avoid the augmentation interrupting a patient's line of sight as the surface of the augmentation may not be sufficiently smooth and may adversely affect the patient's vision.

[0122] Although the plan projection of the augmentation shown in FIG. 11 is drawn as a partial best fit to an iso-elevation line and a partial best fit to a circle, one of ordinary skill in the art may appreciate that the plan projection may be any suitable shape such as, but not limited to, a crescent, or an arc, or a free form curve, or some combination thereof that may also be partial best fits to an iso-elevation line and/or to a circle representing the pupil.

[0123] FIG. 12 shows a schematic plan view 1201 of a corneal augmentation 1205 having a doughnut shape to avoid covering the pupil.

[0124] The cut-out's purpose may be to avoid obscuring a line of sight through the cornea as the surface of the augmentation may not be sufficiently smooth to ensure sufficiently unperturbed transmission of light.

[0125] An outer periphery of the plan projection of a corneal augmentation 1205 having a doughnut shape to avoid covering the pupil may be a free form best fit to an iso-elevation line, or it may be any suitable geometric shape such as, but not limited to, a polygon or a circle, that may also be, in part, a best fit to a selected iso-elevation line. The corneal augmentation may also have a cut-out 1206 shaped and sized to avoid obscuring the pupil, as represented by the 3-mm diameter 807. The plan projection of this cut-out may be a circle that encompasses the 3-mm diameter 807 circle, or it may be a best fit to it. One of ordinary skill in the art may appreciate that the plan projection of the cut-out may also be any suitable free form shape, or polygon, or a combination thereof that may also encompass or be a best fit to the 3-mm diameter 807 circle representing a pupil.

[0126] FIG. 13 shows a flow diagram 1301 showing representative steps in the automated determination of a three-dimensional shape of a corneal augmentation.

[0127] In Step 1301 TOPOGRAPHIC & TOMOGRAPHIC EVALUATION a patient's cornea may be examined using a suitable computer controlled topographic or tomographic instrument such as, but not limited to, a Pentacam?.

[0128] In Step 1302 DETERMINE OPTIMAL 3D SHAPE, a suitably programmed digital processor may take the data obtained in the previous step and calculate an optimal three-dimensional shape for a corneal augmentation to ameliorate a patient's corneal abnormality. This calculation may, for instance, include some or all of the concepts discussed above such as, but not limited to, a relationship between the maximum keratometry and the suitable thickness of the augmentation and having the periphery of the augmentation be, in part, a best fit to one or more iso-deviation in elevation, or iso-power lines. The calculation may also take account of other data that may be provided such as, but not limited to, properties of a patent's other eye or cornea.

[0129] In Step 1303 GENERATE & EXPORT CUTTING FILE the suitably programmed digital processor may convert the optimal three-dimensional shape into a form suitable for use by computer controlled micro-precision shaping machine. This may result in a cutting file formatted in a suitable CAD format. Suitable CAD format file types include, but are not limited to, the well-known STEP and STL file formats.

[0130] FIG. 14 shows a flow diagram 1401 showing representative steps in the automated fabrication of a corneal augmentation.

[0131] In Step 1401 OBTAIN CUTTING FILE the CAD cutting file generated in the process described above may be input to a suitable a computer controlled micro-precision shaping machine. The micro-precision shaping machine may include a femtosecond laser and a computer controlled micro-precision XYZ stage. Such a stage may, for instance, be constructed from components supplied by, for instance, Thorlabs of Newton, NJ. The components may, for instance, include their MLS203-1-Fast XY Scanning Stage and their MZS500-E Z-Axis Piczo Stage.

[0132] In Step 1402 MACHINE OPTIMAL 3D SHAPE, a corneal template mounted on the computer controlled micro-precision XYZ stage the may be translated past the focal point of a suitably powerful femtosecond laser in order to produce the corneal augmentation. This process may be analogous to 3D printing in reverse, i.e., successive layers of material may be removed instead of being added.

[0133] One of ordinary skill in the art may appreciate that although the invention has been described primarily with respect to keratoconus, the inventive methods may be used, or adapted for use, for a variety of other corneal ectasia such as, but not limited to, keratoglobus, pellucid marginal degeneration, posterior keratoconus, post-LASIK ectasia, Terrien's marginal degeneration, and irregular astigmatism.

[0134] One of ordinary skill in the art may further appreciate that although the invention has been described primarily through reference to elevation maps, the inventive steps may also or instead be implemented through the use of other corneal maps such as, but not limited to, pachymetric maps that display the corneal thickness, and axial and tangential maps that display local curvature of the cornea.

INDUSTRIAL APPLICABILITY

[0135] The present inventions may have applicability in the field of optical devices and in the field of corrective eye surgery.