This application was filed as a PCT international patent application on day 5 and 14 of 2015, and claims priority to U.S. patent application serial No. 14/692,960, filed on day 22 of 2015, 4 and 2015, the disclosure of which is incorporated herein by reference in its entirety. U.S. patent application Ser. No. 14/692,960, filed 2013, 7, 10, entitled "REVERSIBLY DEFORMABLE Artificial CORNEA AND method of Implantation" (REVERSIBLY DEFORMABLE ARTIFICIAL CORNEA AND METHODS FOR RIMPLANTATION), is a continuation-in-part of U.S. patent application Ser. No. 13/979,122, U.S. patent application Ser. No. 13/979,122 is a domestic stage of International application No. PCT/US2011/053510 filed 2011, 9, 27, which claims the benefit of U.S. provisional patent application Ser. No. 61/388,386 filed 2010, 9, 30, 35U.S. C.119, the disclosure of which is incorporated herein by reference in its entirety. The U.S. specification claims priority to all of the above-mentioned applications.
Summary of The Invention
The present disclosure overcomes at least some of the problems of prior keratoprostheses noted above. In certain embodiments, the artificial cornea is manufactured for implantation within a layer of the cornea without penetrating into the anterior chamber of the eye. By avoiding such penetration, the risk of eye infection (endophthalmitis) is greatly reduced. In certain embodiments, the keratoprosthesis, or portions thereof, are designed to be sufficiently flexible and durable that they can be implanted through a small incision into the corneal pocket when the size of the entry incision into the pocket is smaller than the size of the keratoprosthesis in its relaxed state. This implantation is advantageous both because it further inhibits the invasion of bacteria surrounding the implant into the anterior chamber and because it helps anchor the implant, which allows the device to self-retain even without sutures or adhesives. However, in general, the implant should be at least somewhat more rigid than the corneal tissue, which will allow the implant to maintain an optically advantageous shape after implantation.
With existing keratoprostheses, they have not been consistently installed to match the natural shape of the cornea. This is important because mismatches between the keratoprosthesis optical element and the corneal surface cause clinically significant problems. In the case of a Boston keratoprosthesis, the height of the optical element is above the level of the carrier donor cornea, causing a constant foreign body sensation to the patient and requiring constant use of a bandage contact lens to prevent abrasion of the conjunctiva on the inner side of the eyelids. Alphacor, on the other handTMIs located 300 microns below the level of the host cornea, which creates a pit or hole that continuously accumulates debris, such as mucus, thereby limiting the patient's vision improvement.
In certain embodiments, the keratoprosthesis is implanted into the cornea using an incision having very precise dimensions. The accuracy of the dimensions allows the keratoprosthesis to be accurately mounted in the cornea such that the surface of the keratoprosthesis is flush with the surface of the optical element of the keratoprosthesis and there is no gap between the optical element and the corneal tissue. The ability to create corneal incisions with this high level of accuracy has only recently become possible with the availability of femtosecond lasers and mechanical corneal pocket makers. In some examples, the corneal incisions are created using a femtosecond laser with a typical tolerance of about +/-3 microns. In further examples, corneal pocket incisions may also be created with a mechanical corneal pocket maker, which typically has a tolerance of +/-50 microns or better. Manually manufactured capsular bags may also be used to implant the keratoprostheses disclosed herein, however, it is not possible to ensure that the optical elements are flush with the surface of the host cornea because the human hand cannot make incisions with a precision of +/-50 microns.
In certain embodiments, the cut that creates the opening for the optical element of the keratoprosthesis of the present disclosure also exactly matches the angle of the optical element, i.e., the cut of the cornea adjacent to the optical element matches the angle of the optical element to within +/-30 degrees, in certain examples +/-10 degrees. For example, if the side of the optical element makes a 90 degree angle with the plane created by the junction of the edge and the optical element, the adjacent corneal incision should also be 90 degrees with the plane created by the junction of the edge and the optical element.
In other examples, a corneal incision is made to remove a volume of corneal tissue that has a shape similar to the three-dimensional shape of the artificial cornea (fig. 9A). This interference or interlocking fit of the keratoprosthesis with the corneal tissue can help retain the device within the cornea, as shown in fig. 9B.
In a specific example of the present disclosure, the keratoprosthesis has a central optical element that is machined to a very tight tolerance to maintain a preselected optical element height within a tolerance of ± 50 μm or less. Since 50 μm is the average thickness of the epithelium on the cornea, and the corneal epithelium is able to respond by thinning or thickening to offset any differences between the surface level of the keratoprosthesis and the native cornea. Thus, by carefully controlling the depth of the corneal pocket to within similar or smaller tolerances, the optical element height of the keratoprosthesis can be matched to the height of the native cornea to protect the eye and tear film above the keratoprosthesis and improve patient comfort. The optical element height is typically maintained between 200 μm and 400 μm to allow the natural corneal tissue to have sufficient thickness to cover the edge of the artificial cornea to reduce the risk of erosion through the tissue. In the case of an abnormally thick cornea, such as is commonly found in patients with corneal edema caused by endothelial failure, the height of the optical element may be as much as 800 μm to compensate for this increased thickness.
Thus, in certain embodiments, a reversibly deformable keratoprosthesis comprises a monolithic body having a central optical element surrounded by an annular rim. By "monolithic" it is meant that the central optical element and the edges are a single, continuous body of material, without seams, joints, etc. For example, the keratoprosthesis may be formed from a single blank or slab of a material, typically a polymeric hydrogel of the type commonly used in forming intraocular lenses (IOLs), such as those commercially available from Benz Research. The polymeric hydrogel material may also have both hydrophobic and hydrophilic properties, such as a copolymer of hydroxyethyl methacrylate and methyl methacrylate that has been subjected to a plasma surface treatment. Alternatively, the keratoprosthesis may be molded, machined or laser cut from a material comprising an interpenetrating network or a collagen-based hydrogel.
The monolithic body has a diameter when hydrated in the range of 4mm to 10 mm. The central optical element has a diameter in the range of 3mm to 9mm and an optical element height (D, fig. 4) in the range of 200 μm to 800 μm. The optical element height is manufactured to tolerances of +/-50 microns or less to allow for a close fit to the surrounding recipient corneal tissue. The annular rim has a ring width in the range of 0.5mm to 4.5mm and a median thickness in the range of 50 μm to 200 μm. In certain examples, the polymeric hydrogel is selected to have a modulus in the range of 0.3MPa to 100MPa when fully hydrated. In certain examples, the tensile strength is at least 1.5MPa and the elongation at break is at least 100%. Suitable host materials should be at least partially permeable to oxygen, typically having an oxygen permeability (dK) of at least 3 barrers. Exemplary materials having excellent oxygen permeability, e.g., a dK of at least 60, include: lotrafilcon A, Lotrafilcon B, Balafilcon A, Comfilcon A, Senofilcon A, Enfilcon A and Galyfilcon A.
In some embodiments, the annular rim of the corneal implant surrounds the posterior edge of the central optical element. Additionally, the anterior surface of the central optical element typically has a convex shape to provide, when implanted in the cornea, a refractive power generally equal to or consistent with that of the native cornea, typically in the range of 30 diopters to 70 diopters. Typically, the front surface of the central optical element has a convex shape and the back surface has a concave shape. The radius of curvature of the posterior optic and edge generally corresponds to the range of curvature of the native cornea, in the range of 6.2mm to 10 mm.
In certain embodiments, the annular rim has a plurality of apertures to allow nutrients and oxygen to pass therethrough. Since the skirt is to be implanted between adjacent layer surfaces of the cornea, it is important that nutrients can pass through it to maintain the health of the corneal tissue. In certain embodiments, the pores comprise 10% to 90% of the annular region of the rim, typically about 33% of the region. In some embodiments, the apertures are circular holes arranged evenly around the annular edge, but they may take a number of other geometries, such as crenellations (crenellations) in the outer edge of the annular edge.
In another example of the present disclosure, a method of implanting a keratoprosthesis into a cornea to replace a damaged central region of the cornea is disclosed that includes forming a central anterior opening having a posterior surface surrounded by a surrounding sidewall in the cornea. In some examples, the openings have a uniform depth, typically in the range of 200 μm to 800 μm, wherein the depth is selected to match the height of the peripheral wall of the central optical element of the implant, in some examples within ± 50 μm. The artificial cornea is implanted within the central anterior opening such that the peripheral thickness or wall height of the central optical element matches the peripheral sidewall of the central anterior opening within a tolerance of ± 50 μm to provide the advantages discussed above.
In a particular embodiment of the method, in addition to forming the central anterior opening, a layered pocket is formed over at least a portion of the peripheral sidewall of the central anterior opening, and an edge portion of the implant is inserted into the layered pocket to anchor the implant in the opening. Typically, the layered capsular bag completely surrounds the central anterior opening and the annular rim extends completely around the implant. In other exemplary embodiments, the layered pocket is formed around a periphery of a posterior surface of the central anterior opening, and an annular rim into the layered pocket is disposed around a posterior edge of a central optical element of the corneal implant.
In certain embodiments, the central anterior opening is formed to have a diameter that is less than the diameter of the central optical element, typically 70% to 99% of the diameter of the central optical element, so that the partially elastic corneal tissue can be tightly sealed around the peripheral wall of the implant to help prevent extrusion of the implant after the sutures are removed, inhibit epithelial ingrowth, inhibit bacterial entry, and prevent aqueous loss from the anterior chamber. The keratoprosthesis may be implanted into the central anterior opening by one of two different techniques. In a first technique, the artificial cornea is constrained (i.e., deformed) to reduce its width and introduced in a posterior direction through the upper surface of the central anterior opening. The keratoprosthesis may be released from its constrained state within the central anterior opening so that it adopts its unconstrained geometry to occupy the volume of the central opening, typically with the annular rim inserted into a laminar pocket. Alternatively, a separate lateral opening may be formed into the central anterior opening from the side of the eye and a constrained keratoprosthesis introduced therethrough.
In certain embodiments, the artificial cornea is adapted to support the growth of a viable corneal epithelium on the periphery of the anterior surface of the optical element. Establishing a viable epithelium on the peripheral anterior surface will advantageously provide a biologic seal around the edge of the anterior surface of the optical element to prevent bacteria from entering the corneal pocket through the junction of the raised optical element and the corneal stroma. In some instances, the center of the optical element remains free of corneal epithelium after implantation, which will allow the central surface of the optical element (which is critical to optical performance) to remain optically smooth even in cases where the patient's eye is unable to form a smooth, optically well-performing epithelium. In certain embodiments, the corneal epithelium of the patient is capable of growing over a width in a range of 0.1mm to 1mm on the periphery of the anterior surface of the optical element.
Promoting growth of living corneal epithelium on the periphery of the anterior optical element may be achieved by coating or covalently bonding certain biomolecules, such as extracellular matrix proteins or growth factors, that promote such growth on the periphery of the anterior surface of the optical element, typically to a width within the ranges set forth above. Suitable biomolecules include collagen, fibronectin, laminin, fibronectin adhesion promoting peptide sequence (H-trp-gln-pro-pro-arg-ala-arg-ile-OH) (FAP), and epidermal growth factor. In other examples, the outer periphery of the optical element can be made porous or textured to allow corneal epithelial cells to more readily bind to the surface of the outer periphery of the anterior side of the optical element.
Many materials that can be used to make artificial corneas generally do not support the growth of corneal epithelial cells without undergoing special surface treatments as described above. In these cases, the artificial cornea may be formed of such a material that does not promote growth, and the outer periphery is treated to promote growth. In the case where the artificial cornea is formed of a material that inherently supports epithelial growth, such as collagen or a collagen derivative, a polymer that does not support epithelial growth, such as silicone or methacrylate, may be coated on the central surface of the optical element to keep the central surface of the optical element free of epithelium.
In certain embodiments, different portions of the keratoprosthesis are made of materials that exhibit different mechanical properties. For example, in certain embodiments, the anchoring portion of the keratoprosthesis is made of a material having different mechanical properties than the material of the optical portion of the keratoprosthesis. In some of these embodiments, the different mechanical properties are achieved by using different materials. In other embodiments, different mechanical properties are achieved by subjecting different portions of a keratoprosthesis made of a single material to different treatments, such as mechanical, radiation (e.g., electromagnetic), thermal, and/or chemical treatments. In other embodiments, the different mechanical properties are achieved by using both different materials and different material treatments. The artificial cornea with different mechanical properties in different parts can improve patient comfort, improve visual quality, reduce the chance of extrusion and improve the ability of the artificial cornea to reversibly deform. In general, a stiffer optical portion results in better optical performance, but may cause more patient discomfort. Generally, the stiffer the anchoring portion, the less likely the keratoprosthesis will spontaneously extrude from the eye, but there may be more discomfort and a greater risk of erosion through corneal tissue over time.
Furthermore, a keratoprosthesis having an optical portion with a first set of mechanical properties and an anchoring portion with a second set of mechanical properties consistent with the present disclosure may allow the keratoprosthesis structure to facilitate nutrient permeability (e.g., by incorporating a large amount of empty space in the anchoring portion) without increasing the risk of post-implantation extrusion.
In certain embodiments, the amount of material used for the anchoring portion of the keratoprosthesis is reduced or minimized. This may reduce the overall weight of the keratoprosthesis, reduce its chances of extrusion, improve its reversible deformation properties and improve the nutrient permeability of the keratoprosthesis.
In view of the above, in one case, a corneal implant includes an artificial cornea for replacing excised corneal tissue, the artificial cornea including a relaxed state and a deformed state and being reversibly deformable such that the artificial cornea can be returned from the deformed state to the relaxed state and can be implanted into an eye through an opening smaller than a width of the artificial cornea in the relaxed state; the artificial cornea further comprises an optical portion and an anchoring portion, the optical portion comprising a material having a first set of mechanical properties and the anchoring portion comprising a material having a second set of mechanical properties.
In another case, a corneal implant comprises an artificial cornea for replacing excised corneal tissue, the artificial cornea comprising a relaxed state and a deformed state and being reversibly deformable such that the artificial cornea is capable of returning from the deformed state to the relaxed state and is implantable into an eye through an opening smaller than a width of the artificial cornea in the relaxed state; the artificial cornea further comprises an optical portion and an anchoring portion, the optical portion comprising a material that has been treated differently than the anchoring portion.
In another case, a corneal implant comprises an artificial cornea for replacing excised corneal tissue, the artificial cornea comprising a relaxed state and a deformed state and being reversibly deformable such that the artificial cornea is capable of returning from the deformed state to the relaxed state and is implantable into an eye through an opening smaller than a width of the artificial cornea in the relaxed state; the artificial cornea further includes an optical portion and an anchoring portion, the optical portion including a material having a first set of mechanical properties, and the anchoring portion including a material having a second set of mechanical properties selected to self-retain the anchoring portion within the cornea.
In another case, a corneal implant comprises an artificial cornea for replacing excised corneal tissue, the artificial cornea comprising a relaxed state and a deformed state and being reversibly deformable such that the artificial cornea is capable of returning from the deformed state to the relaxed state and is implantable into an eye through an opening smaller than a width of the artificial cornea in the relaxed state; the artificial cornea further comprises an optical portion and an anchoring portion, the anchoring portion comprising a material that has been treated differently than the optical portion so as to self-retain the anchoring portion within the cornea.
In another case, a corneal implant comprises an artificial cornea for replacing excised corneal tissue, the artificial cornea comprising a relaxed state and a deformed state and being reversibly deformable such that the artificial cornea is capable of returning from the deformed state to the relaxed state and is implantable into an eye through an opening smaller than a width of the artificial cornea in the relaxed state; the artificial cornea further comprising an optical portion and an anchoring portion; the optical portion comprises a sidewall, a groove (grove) disposed in the sidewall, and a first material; the anchoring portion comprises a second material, an inner ring and an outer ring such that there is an open space between the inner and outer rings and such that the inner ring is joined to the groove; wherein the first material comprises a modulus of elasticity that is different from a modulus of elasticity of the second material; wherein the first material comprises a tensile strength that is different from a tensile strength of the second material; and wherein the first material comprises an elongation at break that is different from the elongation at break of the second material; and wherein at least one of the modulus of elasticity, tensile strength, and elongation at break of the second material is selected to self-retain the anchoring portion within the cornea.
Detailed Description
Various embodiments are described in detail herein with reference to the drawings, wherein like reference numerals represent like parts and assemblies throughout the several views. Reference to various embodiments does not limit the scope of the claims. Furthermore, any examples set forth in this specification are not intended to be limiting and merely set forth some of the many possible embodiments for the claims.
Referring to fig. 1-3, a keratoprosthesis 10, consistent with the principles of the present disclosure, includes a central optical element 12 surrounded by an annular rim 14. A plurality of apertures 16, typically circular holes, are formed completely through the annular rim to allow nutrients to pass therethrough after implantation. As illustrated, the apertures 16 comprise about 33% of the total area of the annular rim 14, but the total opening or void area provided by the apertures may be any value in the range of 10% to 90% of the total area.
In some instances, the keratoprosthesis 10 is formed as a monolithic structure, i.e., a structure without seams or joints, and in some instances is formed from a single blank or piece of material. For example, the artificial cornea 10 may be machined from a block of suitable hydrogel polymer.
Optionally, the outer perimeter of the anterior surface of the central optical element may be modified (or left unmodified) to support epithelial growth over an annular region having a width typically in the range of 0.1mm to 1 mm. As described above, the annular region (bounded by dashed line 32) may be modified by coating or depositing a material that promotes epithelial growth, as the material of the central optical element inherently inhibits epithelial growth. Roughening the texture of the annular region or making the annular region porous may also promote epithelial growth on the annular region.
Typical ranges and values for the dimensions of the artificial cornea 10 are set forth in table 1 below, with reference to fig. 4-5. These dimensions are given to the keratoprosthesis in a fully hydrated state:
| dimension (d) of | Specific value | Tolerance of |
| D | 0.200mm | ±0.050mm |
| Ri | 7.6mm | ±0.127mm |
| Ro | 7.7mm | 0.127mm |
| Rc | 0.1mm | Reference device |
| Rf | 7.6mm | ±0.127mm |
| Of | 0.05mm | ±0.050mm |
| Oo | 0.256mm | ±0.050mm |
| A | 90° | ±100 |
| Da | 0.8mm | ±0.127mm |
| Df | 8mm | ±0.254mm |
| Dco | 4mm | ±0.127mm |
| Dh | 5.25mm | Reference device |
Although in some examples the annular rim 14 includes an aperture 16, such as a circular hole, it is more desirable that at least the innermost region of the annular rim adjacent the outer peripheral wall 22 and the central optical element 12 (fig. 1-3) remains solid. This solid portion of the rim immediately adjacent the optical element helps prevent bacterial entry and epithelial cell invasion in the event that the posterior cornea behind the optical element has been excised, which may be necessary when the posterior cornea is very opaque. In certain examples, the width W (fig. 3) of the solid material is maintained in the range of 0.25mm to 0.75 mm. Thus, the apertures or other open areas of the rim are disposed radially outward from the solid area.
In other embodiments, the edge 114 around the central optical element 112 may be discontinuous or, as shown in fig. 8A, may be constructed of a material having a hollow section or scaffold structure. Other variations include a discontinuous edge 214 (fig. 8B) surrounding the central optical element 212, a ring-shaped edge 314 (fig. 8C) having a rectangular or elliptical (oblong) cutout surrounding the central optical element 312, and a shelf edge 414 (fig. 8D) surrounding the central optical element 412. In some examples of these embodiments, the edge 114, 214, 314, or 414 has one or more mechanical properties that are different from one or more mechanical properties of the central optical element 112, 212, 312, or 412, respectively. In some examples of these embodiments, the edge 114, 214, 314, or 414 is made of a different material than the central optical element 112, 212, 312, or 412, respectively.
In other embodiments, fig. 9A shows a volume of tissue 440 that has been removed from a cornea 442. Figure 9B shows a corneal implant 450 configured to match the volume of removed tissue 440 shown in figure 9A. In certain examples of these embodiments, the edge 454 has one or more mechanical properties that are different from one or more mechanical properties of the central optical element 452. In some examples of these embodiments, the edge 454 is made of a different material than the central optical element 452.
Referring now to fig. 6A to 6F, implantation of the keratoprosthesis 10 of the present disclosure into the cornea C will be described. As shown in fig. 6A, a cornea C is shown having an opaque or other optically irregular area generally present in its central region. To introduce the artificial cornea 10, the central region of the cornea is cut away and removed as shown in fig. 6B. The cutting may be effected in a conventional manner, typically using a femtosecond laser, optionally in combination with a mechanical trepan, to cut out the cylindrical pockets in the posterior direction. In keratoprosthesis implantation consistent with the present disclosure, it is very important that the depth of the pocket be carefully controlled, particularly around the outer periphery. For a cornea with an average thickness of 500 to 600 μm, the depth is typically controlled to be about 200 to 400 μm below the surface of the cornea, leaving sufficient corneal posterior thickness to prevent perforation beneath the pocket. In the case of an abnormally thick cornea, such as is commonly found in the case of corneal edema caused by endothelial disorders, the depth of the pocket can be as high as 800 μm to compensate for the increase in corneal thickness. As shown in fig. 6B, the resulting capsular bag has a posterior wall PW. After the pocket P has been formed, an annular pocket AP is formed around the peripheral base of the central pocket P as shown in fig. 6C. Alternatively, a laminar pouch is first created in which the posterior wall PW and annular pouch AP are continuous, and then the central region CR is removed to create the anterior opening. The dimensions of the primary and annular pockets are selected to be compatible with the dimensions of the keratoprosthesis 10 described above. For example, if the keratoprosthesis has the dimensions set forth in Table 1, the pocket should be 200 μm deep, the diameter of the pocket should be 3.5mm, and the outer diameter of the annular pocket AP extending around the central pocket P should be 8.5 mm.
Once the central pocket P and the annular pocket AP are formed, the keratoprosthesis 10 may be folded or otherwise constrained (i.e., deformed) as shown in fig. 6B and inserted into the central pocket P in a posterior direction. When the keratoprosthesis 10 is inserted, the constraint can be released to allow the annular rim 14 to open radially outward and into the annular pocket AP, as shown in figure 6E. The keratoprosthesis 11 may then optionally be sutured in place, typically using absorbable nylon sutures. Generally, the keratoprosthesis of the present disclosure will self-leave within the cornea even without sutures.
Alternatively, as shown in fig. 6F, the keratoprosthesis 10 may be introduced through a lateral incision LI formed to provide access. The use of lateral cuts may be an option when forming the pockets, for example, using a pocket making machine as described in commonly owned U.S. patent No. 7,223,275.
In fig. 7A, the central optical element 112 of the Boston keratoprosthesis is higher than the surface of the donor carrier cornea, which would cause irritation by abrading the lining of the patient's eyelid. In FIG. 7B, AlphacorTMis located below the surface of the cornea, which creates a pocket that will accumulate mucus and debris, thus obscuring the patient's vision in figure 7C, the edge of the central optical element 12 of the keratoprosthesis of the present disclosure is at the same level as the surrounding cornea, furthermore, there is no gap between the surrounding corneal tissue and the optical element because the opening size of the cornea is slightly smaller than the diameter of the optical element to provide a snug fit.
Figure 10 is an anterior (i.e., anteriorly positioned) view of another embodiment of a corneal implant consistent with the present disclosure shown in a relaxed state. Corneal implant 500 includes a keratoprosthesis 502, an optical portion 504 having an anterior surface 505, and an anchoring portion 506. In this example, the anchor portion 506 includes a stent 507 having an inner ring 508, an outer ring 510, and at least one connecting element 512. A blank space 514 is shown between the inner ring 508 and the outer ring 510.
The artificial cornea 502 is configured to replace ablated corneal tissue in the eye of a patient. In certain examples, the keratoprosthesis 502 is configured to replace a portion of the full thickness of corneal tissue; in other examples, the keratoprosthesis 502 is configured to replace a portion of a partial thickness of corneal tissue. In certain examples, the artificial cornea 502 replaces corneal stromal tissue, which may include ablation from an anterior portion of the stroma, a posterior portion of the cornea, or both an anterior portion and a posterior portion of the cornea. In some instances, the keratoprosthesis 502 replaces corneal tissue that was ablated in front of the Descemet's membrane, i.e., a non-penetrating, partial thickness procedure. In some instances, the keratoprosthesis 502 replaces the full thickness of ablated corneal tissue, including the Descemet's membrane and endothelium, i.e., a penetrating, full thickness procedure. In some examples, the keratoprosthesis 502 allows epithelial growth on an anterior surface (e.g., anterior surface 505) after implantation. In some of these embodiments, one or more portions of the anterior surface of the keratoprosthesis are treated or modified in accordance with the above disclosure to promote new epithelial growth on a portion or the entire anterior surface 505.
In exemplary corneal implant 500, optical portion 504 is shaped to restore and/or improve vision in the eye in which it is implanted. Thus, in some examples, optic portion 504 is shaped like a lens such that it can refract light entering the patient's eye. In addition, the optical portion 504 is transparent or substantially transparent to transmit light through the eye. The exact size and shape of the optical portion 504 may vary in accordance with the above disclosure. Some examples of materials suitable for optical portion 504 have been previously described. In general, the optical portion 504 may be made of any transparent substance and may or may not be reversibly deformable. Thus, in some examples, the optical portion 504 is made of a transparent polymer (e.g., silicone, acrylic). In other examples, the optic portion 504 is made of collagen, either natural (e.g., from human or animal sources) or synthetic. In other examples, the optical portion 504 is made of a non-deformable solid such as glass or a crystal such as sapphire or diamond. In other examples, the optical portion 504 is made of a plurality of different materials. In certain examples, the optical portion has a circular perimeter, such as the perimeter of the front surface 505 of the optical portion 502. The diameter of such an optical portion 504 is typically in the range of about 3mm to about 9 mm. In an alternative example, the optic portion 502 has a polygonal or irregular perimeter, wherein the maximum distance between two points on the polygonal perimeter is in the range of about 3mm to about 9 mm. Depending on the material selected for the optical portion 502, the optical portion 502 may be manufactured in any suitable manner, such as by machining the optical portion 502 from a block of material, or molding (e.g., injection molding).
The exemplary optical portion 504 includes a front surface 505. Depending on the patient and the particular portion of the cornea being ablated and replaced, the anterior surface 505 may be embedded in the stroma, may abut the anterior surface of the stroma, or may be located anterior to the anterior elastic layer. In some examples, anterior surface 505 is configured based on refractive properties of other portions of the eye of the patient in which anterior surface 505 is implanted to provide improved or enhanced vision to the eye. In some examples, the front surface 505 is convex. The degree of protrusion can be modified to accommodate the particular optical characteristics of the patient's eye.
An exemplary anchor portion 506 extends from the optical portion. The primary purpose of anchoring portion 506 is to retain corneal implant 500 in place in the eye and to avoid extrusion of corneal implant 500, ideally without sutures or other fixation means (e.g., glue), i.e., corneal implant 500 should be self-retaining. In some examples, anchor portion 506 surrounds optical portion 504. In some examples, the anchor portion 506 includes a frame or scaffolding structure that is largely comprised of empty spaces, such as empty space 514 shown in fig. 10. In this example, the anchoring portion 506 is a bracket 507 that includes an inner ring 508 that surrounds, contacts, and mounts to the wall of the optical portion 504 and an outer ring 510 that is wider than the inner ring. The inner ring 508 and the outer ring 510 are connected by one or more connecting elements 512. In some instances, there is only one connection element 512. In other examples, there are 2, 3, 4, or more connection elements 512. In certain examples containing multiple connecting elements 512, the connecting elements 512 are evenly spaced from one another within the anchor portion 506. Between adjacent connecting elements 512 is a void space 514. In an alternative embodiment, the stent 507 is comprised of 3 or more rings, with adjacent rings being interconnected by one or more connecting elements 512.
Various aspects of anchoring portion 506 (e.g., inner ring 508, outer ring 510, and one or more connecting elements 512) may be thicker or thinner depending on the particular characteristics desired for corneal implant 500, such as strength, size, weight, material, reversible deformability, self-retaining ability of artificial cornea 502 within the patient's cornea, and the like. For example, one or more of the various aspects of the anchoring portion 506 may be made thinner to increase or maximize the amount of empty space 514 and/or to enhance the self-retention of the keratoprosthesis 502 within the patient's cornea. In addition, anchor 506 made from a thinner component may be more flexible than an anchor comprising a thicker component. In some examples, the outer ring 510 of the anchoring portion 506 is in a range of about 1mm to about 4.5mm from the optical portion 504 when the keratoprosthesis 502 is in a relaxed state. The empty space 514 allows for improved corneal nutrition, as oxygen and other nutrient molecules can easily pass from the anterior portion of the cornea to the posterior portion of the cornea, and vice versa, through the empty space 514 in the corneal implant 500. It should be clear that the empty space 514 is not empty after implantation into the cornea, but becomes filled with the patient's natural surrounding corneal tissue. This would occur, for example, if the anchoring portion 506 of the keratoprosthesis 502 were implanted in a corneal pocket surrounding the ablated corneal tissue (the optical portion 504 would replace the ablated tissue).
In order to allow the anchoring portion 506 toSelf-retention of corneal implant 500, the sum of the frictional force of anchoring portion 506 against corneal tissue and the force required to deform anchoring portion 506 to a shape less than the diameter of optical portion 504, must not be exceeded by the force applied against the surface of artificial cornea 502, including anterior surface 505. One such force is the force of the eyelid against the cornea, which is estimated to be 40 to 80g/cm2The maximum pressure in between. In fact, however, this range is used only as a minimum amount of expected pressure, as some patients may rub their eyes and apply pressures significantly higher than these. There may also be a traumatic environment where the pressure applied to the corneal surface will also exceed the pressure created by anchoring portion 506. Thus, in certain embodiments, the anchoring portion 506 is designed to have mechanical properties that allow it to resist movement within the corneal pocket, at least under normal physiological conditions.
In some examples, the friction of anchoring portion 506 within the cornea is increased (i.e., the self-retention properties of artificial cornea 502 are enhanced) by increasing the area of open spaces 514 in anchoring portion 506, thereby allowing more corneal tissue to be captured within each open space 514. The physical engagement between the corneal tissue within open space 514 and the rest of anchoring portion 506 increases friction. Additionally or alternatively, the friction between corneal implant 500 and the cornea may be increased by selecting a material for anchoring portion 506 that has a relatively high coefficient of friction. A chemical treatment or coating on the anchoring portion 506 may also increase the coefficient of friction.
The force required to deform anchoring portion 506 can also be manipulated by changing its mechanical properties. For example, increasing the Young's modulus, tensile strength, and/or compressive strength of the material selected for anchoring portion 506 will increase the amount of force necessary to deform anchoring portion 506 and thus improve retention of corneal implant 500 in the eye.
In certain examples, the anchoring portion 506 is machined or molded, as appropriate, from any one or more of the various reversibly deformable materials described, for example, above. Additionally, in some examples, the support 507 is manufactured as a single integral piece, or as multiple pieces that are subsequently joined together. The various parts of the stent 507 (e.g., the inner ring 508, the outer ring 510, and the connecting elements 512) may be connected together by any suitable means, such as glue, welding, chemical bonding, or mechanical fit.
While the inclusion of empty space 514 within anchoring portion 506 of artificial cornea 502 theoretically reduces the structural stability of anchoring portion 506 and thus its ability to retain and anchor artificial cornea 502 within a patient's eye, the particular structure (e.g., scaffold 507) and/or the fact that the anchoring material of anchoring portion 506 may be stronger or otherwise more structurally sound than optical portion 504 overcomes any of these perceived disadvantages of utilizing an anchoring portion with a larger open space while providing the advantage of improved nutrient penetration.
In some embodiments, optical portion 504 is made of a material having one or more mechanical properties that are different from those of anchor portion 506. Examples of such mechanical properties include, but are not limited to: compressive strength (the stress a material can withstand before it fails in compression); creep (slow and gradual deformation of the object over time); ductility (the ability of a material to deform under a tensile load); elongation at break; fatigue limit (the maximum stress a material can withstand under repeated loading); a flexural modulus; bending strength; fracture toughness (energy absorbed per unit area before the material fractures); hardness (ability to resist dishing); plasticity (the ability of a material to undergo irreversible deformation); poisson's ratio (ratio of transverse strain to axial strain); resiliency (the ability of a material to absorb energy when elastically deformed); shear strain; shear strength; shear modulus (ratio of shear strength to shear strain); specific modulus (modulus per unit volume); specific strength (strength per unit density); tensile strength (the maximum tensile stress a material can withstand before failure); yield strength (the stress at which the material begins to yield); young's modulus (ratio of linear stress to linear strain); coefficient of friction on the surface of the material; and a coefficient of restitution.
Selecting materials with different mechanical properties for the optical portion 504 and the anchoring portion 506 results in a keratoprosthesis 502 with a variety of different characteristics. For example, a keratoprosthesis 502 having a relatively stiff (e.g., higher young's modulus) optic portion 504 improves the optical regularity of the refractive surface (e.g., anterior surface 505) of the optic portion 504, resulting in better vision for the patient. On the other hand, a keratoprosthesis 502 having a relatively flexible (e.g., lower young's modulus) optic portion 504 may result in a refractive surface having less than optimal optical regularity, while providing a more comfortable implant for the patient, which may require less accommodation after implantation. Conversely, a stiffer optical portion 504 may require the use of a soft, bandaged contact lens over the optical portion 504 in order to provide an acceptable level of comfort to the patient.
With respect to the mechanical properties of the anchoring portion 506, an anchoring portion 506 having a relatively stiff (e.g., higher young's modulus) allows the anchoring portion 506 to be made primarily of empty spaces (e.g., empty spaces 514), which is advantageous for reasons such as those discussed above, while still providing a secure and/or self-retaining anchoring of the keratoprosthesis 502 within the corneal pocket. On the other hand, having relatively flexible anchoring portions may improve patient comfort but may reduce retention of the stability.
In order to optimize different characteristics of the keratoprosthesis, such as optical quality, comfort and retention, it is advantageous to provide a reversibly deformable keratoprosthesis 502 having multiple regions with different mechanical properties. In certain particular embodiments, it may be advantageous to provide a keratoprosthesis 502 having an optical portion 504 with different mechanical properties than its anchoring portion 506 in order to optimize different characteristics of the implant, such as optical quality, comfort, and retention.
Providing a keratoprosthesis 502 having a first set of mechanical properties for optical portion 504 and a second set of mechanical properties for anchoring portion 506 may be accomplished, for example, by differential material selection and/or differential processing of the same material as described above. In some embodiments of the keratoprosthesis 502 in a relaxed state, the optical portion 504 is formed by a sapphireA stone crystal and having a diameter D in the range of about 3mm to about 7mm2(FIG. 12), a thickness T in the range of about 150 μm to about 900 μm2(FIG. 12), a refractive index in the range of about 1.7 to about 1.8, a refractive index parallel to the corneal axis A in the range of about 300GPa to about 600GPa at about 25 ℃1(FIG. 14) Young's modulus, modulus of rigidity (shear modulus) in the range of about 100GPa to about 300GPa, Poisson's ratio in the range of about 0.2 to about 0.4 depending on orientation, parallel to the corneal axis A in the range of about 900MPa to about 1200MPa at about 25 ℃1(FIG. 14) flexural strength, perpendicular to the corneal axis A in the range of about 500MPa to about 1000MPa at about 25 ℃1(FIG. 14) a flexural strength, a compressive strength in the range of about 1.5GPa to about 2.5GPa at about 25 ℃, a hardness in the range of about 8 to about 10 (Mohs hardness) (at about 20 ℃ to about 25 ℃), which corresponds to a value parallel to the corneal axis A1(FIG. 14) a range of about 1800 Knoop to about 2000 Knoop and perpendicular to the corneal axis A1(FIG. 14) a range of about 2100 Knoop to about 2300 Knoop.
In certain embodiments of the keratoprosthesis 502 in a relaxed state, the anchoring portion 506 is made of a nickel titanium alloy having a maximum diameter D in the relaxed state in the range of about 5mm to about 10mm3(fig. 13), an ultimate tensile strength in the range of about 600MPa to about 1200MPa, an elongation at break in the range of about 10% to about 20%, a yield strength in the range of about 50MPa to about 150MPa (at about 5 ℃), an elastic modulus in the range of about 20GPa to about 40GPa at about 5 ℃, and a poisson's ratio in the range of about 0.2 to about 0.4.
In a specific example of the keratoprosthesis 502 in a relaxed state, the optical portion 504 has a diameter D of about 4mm2A thickness T of about 400 μm2(from the front surface 505 to the back end 522 (see FIG. 11)), a refractive index of about 1.7682, a parallel to the corneal axis A of about 435GPa at about 25 ℃1(FIG. 14) Young's modulus, modulus of stiffness (shear modulus) of about 175GPa, Poisson's ratio in the range of about 0.27 to about 0.30 depending on orientation, parallel to the corneal axis A of about 1035MPa at about 25 ℃1(FIG. 14) perpendicular to the corneal axis A of about 760MPa1(FIG. 14) flexural Strength of about 2GPa at about 25 ℃Compressive strength, hardness of about 9 (Mohs hardness) at about 20 ℃ to 25 ℃, which corresponds to a hardness of about 1900 Knoop parallel to the corneal axis A1(FIG. 14) and about 2200 Knoop perpendicular to the corneal axis A1(fig. 14) hardness; and the anchoring portion 506 is made of a nickel titanium alloy having a maximum diameter D of about 7mm3An ultimate tensile strength in the range of about 754MPa to about 960MPa, an elongation at break of about 15.5%, a yield strength of about 100MPa at about 5 ℃, an elastic modulus of about 28GPa at about 5 ℃, and a Poisson's ratio of about 0.3.
The specific example just described above allows the implantation of a keratoprosthesis 502 having a substantially perfect optical surface (corresponding to the front surface 505 of the optical portion 504) into the cornea (sapphire is often used in the most delicate optical applications, such as for focusing lasers). In addition, the nitinol anchoring portion 506 is sufficiently flexible that the anchoring portion of the keratoprosthesis is reversibly deformable and allows it to be implanted through a corneal incision that is as small as (or less than) half the diameter of the entire keratoprosthesis in its relaxed state. Another particularly useful property of nitinol is that it can be manufactured to have a shape memory such that the anchor portion 506 has a high ductility at low temperatures (e.g., about 5 ℃) and will return to its relaxed state after deformation. In certain other metal alloys, nitinol can also be fabricated to be superelastic, which provides the alloy with spring-like properties so that it can serve as the reversibly deformable anchor portion 506. In some examples, one or more portions of corneal implant 500 are made of one or more materials having shape memory. In one example, the anchoring portion 506 is made of a material having a shape memory such that the surgeon can immerse the artificial cornea 502 in cold sterile water (e.g., about 5 ℃) and easily insert the anchoring portion 506 deep into the cornea, and then observe that as the anchoring portion 506 reaches body temperature (about 37 ℃), it automatically partially or fully expands to its relaxed state to secure the artificial cornea 502 in the cornea.
Figure 11 is a front perspective view showing the corneal implant 500 of figure 10 in a relaxed state. As discussed above, exemplary corneal implant 500 includes a keratoprosthesis 502, an optical portion 504 having an anterior surface 505, an anchoring portion 506 having a cradle 507, an inner ring 508, an outer ring 510, at least one connecting element 512, and a void space 514 between inner ring 508 and outer ring 510. Further, in this example, the optical portion 504 includes an outer sidewall 520 and a back end 522.
The outer sidewall 520 extends around the entire optical portion 504. In this example, inner ring 508 of anchor portion 506 mates with outer sidewall 520 between front surface 505 and rear end 522 of optical portion 504 to couple optical portion 504 to anchor portion 506. Also in this example, the outer ring 510 is behind (posterior to) the inner ring 508 and is nearly flush with the posterior end 522 of the anchor portion 506. In an alternative embodiment, the outer ring 510 and the inner ring 508 are in or approximately in the same plane when the keratoprosthesis 502 is in a relaxed state. In some examples, this plane intersects optical portion 504 at a location between front surface 505 and back end 522. Accordingly, it should be appreciated that the connection elements 512 may have any suitable shape and configuration to connect the inner ring 508 to the outer ring 510. In the example shown in fig. 11, each connecting element is approximately L-shaped. In an alternative non-limiting example, one or more of the connection elements 512 is linear. In some examples, one or more portions of one or more connecting elements 512 are straight or curved.
In some examples, optical portion 504 and anchor portion 506 are fabricated separately and joined together for assembly. In other examples, the optical portion 504 and the anchoring portion 506 are manufactured together as a single piece, and then one or more regions of the keratoprosthesis 502 are exposed to one or more material treatments.
Figure 12 is a side view showing the optical portion 504 of the corneal implant of figure 10 in a relaxed state. As discussed above, the exemplary optical portion 504 includes a front surface 505, outer sidewalls 520, and a rear end 522. Further, in this example, the optical portion 504 includes a groove 530.
The groove 530 is arranged in the outer sidewall 520 between the front surface 505 and the back end 522 of the optical portion 504. In this example, the groove is continuous and extends around the entire outer sidewall 520. In alternative examples, the grooves 530 are segmented or otherwise discontinuous. The inner ring 508 mates with (matted with) or otherwise couples to the groove 530. In some examples, this is accomplished by a mechanical or frictional fit, with the groove 530 sized to matingly receive the inner ring 508. Further, glue or other attachment means may be used in addition to the groove 530 or instead of the groove 530 to secure the inner ring 508 to the optical portion 504. The precise location of the groove 530 in the outer sidewall 520 of the optic portion 504 may be selected based on the particular conditions and parameters set forth for the particular patient, resection, and implantation in question.
Figure 13 is a side view illustrating an exemplary anchoring portion 506 of the corneal implant of figure 10 in a relaxed state. As discussed above, the exemplary anchoring portion 506 includes a stent 507 having an inner ring 508, an outer ring 510, one or more connecting elements 512, and a void space 514. Further, in this example, the anchor portion 506 includes a front end 540 and a rear end 542. In some examples, the posterior end 542 is posterior (i.e., posterior) to the posterior end 522 (fig. 11) of the optical portion 504 (fig. 11) when the keratoprosthesis 502 (fig. 11) is in a relaxed state. In some examples, the posterior end 542 is flush with the posterior end 522 when the keratoprosthesis 502 is in a relaxed state. In other examples, when the keratoprosthesis 502 is in a relaxed state, the inner ring 508 and the outer ring 510 are in the same plane such that the anterior end 540 and the posterior end 542 of the stent 507 are also in the same plane (i.e., the anchoring portion 506 is substantially flat). In either of the above examples, the positioning of the anterior end 540 relative to the posterior end 542 may change as the keratoprosthesis 502 is moved into the deformed state. This will be discussed further in connection with fig. 14-15. In alternative examples of the stent 507 shown in the figures, the stent 507 may include other retaining rings and/or support structures.
Figure 14 is a side view of corneal implant 500 of figure 10 shown in an exemplary deformed state with the anchoring portion deformed and the optical portion relaxed; figure 15 is a side view of corneal implant 500 of figure 10 shown in an exemplary deformed state in which the implant is deformed in both the anchoring portion and the optical portion. As shown in fig. 14-15, corneal implant 500 includes a keratoprosthesis 502, an optical portion 504 having an anterior surface 505, an outer sidewall 520, and a posterior end 522, and an anchoring portion 506 having an inner ring 508, an outer ring 510, one or more connecting elements 512, a void space 514, an anterior end 540, and a posterior end 542, as described above.
As shown in figure 14, the outer ring 510 and the connecting member 512 have been reversibly deformed, reducing the width of the keratoprosthesis 502. In this example, the optical portion 504 may or may not be deformable and/or reversibly deformable. The deformation of the outer ring 510 and the connecting element 512 prior to implantation of the keratoprosthesis into the eye is advantageous because the reduced width enables the keratoprosthesis to be implanted through an incision that is smaller than the width of the keratoprosthesis in its relaxed state. In some examples, deformation of the keratoprosthesis 502 allows the keratoprosthesis 502 to be implanted through an incision that is less than half the width of the keratoprosthesis in a relaxed state. A smaller incision reduces the chance of extrusion after implantation and increases the chance of self-retention (i.e., without the use of sutures, glue, or other attachment means). Once inserted through the incision, the keratoprosthesis 502 partially or completely returns to its relaxed state while the optic partially fills (partially or completely) the cut in the corneal tissue, and at least a portion of the outer ring 510 and the connecting element 512 are disposed within a corneal pocket surrounding the edge of the cut. In some examples, the reversible deformation of the keratoprosthesis 502 is achieved without any portion of the keratoprosthesis 502 touching another portion of the keratoprosthesis 502 prior to insertion into the eye, such as without any non-adjacent points on the outer ring 510 touching each other, or without the outer ring 510 touching the optical portion 504, or without any points on the outer ring 510 touching any points on the inner ring 508, or without any points on the outer ring 510 or the inner ring 508 touching any non-adjacent points on any connecting elements 514.
As shown in fig. 15, the outer ring 510, the connecting element 512, and the optical portion 504 have all been reversibly deformed, further reducing the width of the keratoprosthesis 502 (when compared to fig. 14). Thus, in the example shown in fig. 15, both the optical portion 504 and the anchoring portion 506 are reversibly deformable. This deformation is advantageous prior to implantation of the keratoprosthesis into the eye, as the reduced width enables the keratoprosthesis to be implanted through an incision that is smaller than the width of the keratoprosthesis in its relaxed state, as in the deformation of figure 14. A smaller incision (in this case, even smaller than that required to implant the deformed keratoprosthesis of fig. 14) reduces the chance of extrusion after implantation and increases the chance of self-retention (i.e., without the use of sutures, glue, or other attachment means). Once inserted through the incision, the keratoprosthesis 502 partially or completely returns to its relaxed state while the optical portion 504 fills (partially or completely) the cut in the corneal tissue and at least a portion of the outer ring 510 and the connecting element 512 are disposed within the corneal pocket surrounding the cut.
Figure 16 is a side cross-sectional view of another embodiment of a corneal implant consistent with the present disclosure, showing the corneal implant in a relaxed state; figure 17 is a front (i.e., anterior) view of the corneal implant of figure 16, showing the corneal implant in a relaxed state. As shown in fig. 16-17, corneal implant 550 includes a keratoprosthesis 552, an optical portion 554 having an anterior surface 556, a posterior end 558, and an outer sidewall 560. Corneal implant 550 also includes an anchor portion 562 that includes a skirt (skirt) 564.
In some examples, the keratoprosthesis 552 is configured to replace a portion of the full thickness of corneal tissue; in other examples, the keratoprosthesis 552 is configured to replace a portion of a partial thickness of corneal tissue. In certain examples, the artificial cornea 552 replaces corneal stromal tissue, which may include resection from an anterior portion of the stroma, a posterior portion of the cornea, or both an anterior portion and a posterior portion of the cornea. In some instances, the keratoprosthesis 552 replaces corneal tissue that has been ablated in front of the Descemet's membrane, i.e., a non-penetrating, partial thickness procedure. In some instances, the keratoprosthesis 552 replaces the full thickness of ablated corneal tissue, including the Descemet's membrane and endothelium, i.e., a penetrating, full thickness procedure. In some examples, the keratoprosthesis 552 allows epithelial growth on the anterior surface after implantation. In certain of these embodiments, one or more portions of the anterior surface of the keratoprosthesis 552 are treated or modified in accordance with the above disclosure to promote new epithelial growth.
In this exemplary keratoprosthesis 552, a skirt 564 surrounds the optic portion 554, protruding from an outer sidewall 560 of the optic portion 554 at a location between an anterior surface 556 and a posterior end 558 of the optic portion 554. In certain examples, either of the optical portion 554 and the anchoring portion 562 is reversibly deformable to allow the artificial cornea 552 to be implanted through an incision that is smaller than the width of the artificial cornea 552 in a relaxed state. In some instances, deformation of the keratoprosthesis 552 allows the keratoprosthesis 552 to be implanted through an incision that is less than half the width of the illustrated keratoprosthesis in the relaxed state. In other examples, both optical portion 554 and anchor portion 562 are reversibly deformable. Once inserted through the incision, the keratoprosthesis 552 partially or completely returns to its relaxed state while the optic partially fills (partially or completely) the cut in the corneal tissue, and at least a portion of the skirt 564 is disposed within a corneal pocket that partially or completely surrounds the cut.
Depending on the patient and the parameters and characteristics of the particular procedure to be performed, skirt 564 may be made thicker or thinner (as measured from the anterior side to the posterior side) and wider or narrower (as measured outward from optic portion 554). Skirt 564 is implanted into a corneal pocket surrounding a corneal resection and optical portion 554 fills (partially or completely) the resected portion of the cornea after implantation. In this exemplary embodiment, skirt 564 and optic 554 are constructed from materials having one or more different mechanical properties, including but not limited to those described above. In some examples, this is accomplished by fabricating skirt 564 and optic 554 from different materials. Additionally or alternatively, skirt 564 and optic 554 are subjected to different material treatments from one another, such as mechanical, thermal, radiation (e.g., electromagnetic radiation), and/or chemical treatments. In some of these examples, only one or a portion of the optical portion 554 and anchoring portion 562 are treated in this manner to obtain a reversibly deformable keratoprosthesis 552 having regions of different mechanical properties.
The artificial cornea 552 is machined or molded as a single integral unit. Alternatively, skirt 564 and optic 554 are manufactured separately and then joined together by any suitable means, such as glue, welding, and/or a mechanical/friction fit.
Figure 18 is an anterior (front) view of a modified version of the corneal implant embodiment shown in figures 16-17. As discussed above, corneal implant 550 includes a keratoprosthesis 552, an optical portion 554 having an anterior surface 556, and an anchor portion 562 including a skirt 564. Further, in this embodiment, the skirt contains one or more apertures 570. The one or more apertures 570 allow passage of oxygenated nutrients, in accordance with the disclosure above. Skirt 564 (or portions thereof) and optic 554 (or portions thereof) have one or more different mechanical properties, as described above in connection with fig. 16-17.
While the above is a complete description of certain embodiments of the invention, various alternatives, modifications, and equivalents may be used. Accordingly, the above description should not be taken as limiting the scope of the invention, which is defined by the appended claims.