Abstract:
An ophthalmic lens system comprises a lens body with a curved outer surface and an assembly including a plurality of spaced apart nanostructures. The assembly covers at least a portion of the curved outer surface.

Description:
RELATED APPLICATION 
     This application claims priority to U.S. provisional application Ser. No. 61/472,948, filed on Apr. 7, 2011, the contents which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     This disclosure relates in general to ophthalmic lenses and more particularly to ophthalmic lenses that have nanostructured thin film surfaces that reduce surface reflection. 
     BACKGROUND 
     Age, disease, trauma, or a combination thereof may result in deterioration in vision which may be corrected through the use of ophthalmic lenses. Ophthalmic lenses may include lenses positioned externally of the eye or implanted in the eye. Lenses positioned externally of the eye include spectacle lenses and contact lenses. Implanted lenses include intraocular lenses (“IOLs”). An “aphakic IOL” may be used to replace a natural lens of any eye that has, for example, developed a cataract. A “phakic IOL” is generally used with the natural lens intact. The phakic IOL may be located in either the anterior chamber (i.e., in front of the natural lens and the iris) or the posterior chamber (i.e., in front of the natural lens, but behind the iris). 
     Traditionally, the surface reflectance and scattering of light caused by ophthalmic lenses has been considered undesirable. For example, the reflectance may be cosmetically undesirable for persons who are on camera or photographed. Reflectance may also interfere with the physical examination of the eye. Some lens wearers also report glare, halos, dysphotopsia, reflections, and other undesirable images associated with reflective lenses. 
     Traditional anti-reflection coatings formed of uniform and polished anti-reflection layers have shortcomings. For example, the ability to reduce reflection may be limited by the available material&#39;s refractive index. Traditional coatings often require multiple layers and work only for a limited range of reflection angles. Additionally, traditional coatings often use rigid materials that interact poorly with biological tissue. 
     Accordingly, new systems and methods are needed to reduce reflection associated with ophthalmic lenses. 
     SUMMARY 
     In one exemplary aspect, an ophthalmic lens system comprises a lens body with a curved outer surface and an assembly including a plurality of spaced apart nanostructures. The assembly covers at least a portion of the curved outer surface. 
     In another exemplary aspect, a method of forming an ophthalmic lens comprises providing a lens body with a curved outer surface and modifying at least a portion of the curved outer surface to include first assembly including a plurality of spaced apart nanostructures. The first assembly covers at least a portion of the curved outer surface. 
     Further aspects, forms, embodiments, objects, features, benefits, and advantages of the present invention shall become apparent from the detailed drawings and descriptions provided herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the accompanying drawings, which are incorporated in and constitute a part of the specification, embodiments of the invention are illustrated, which, together with a general description of the invention given above, and the detailed description given below, serve to exemplify the embodiments of this invention. 
         FIG. 1  is an ophthalmic lens with a nanostructure assembly. 
         FIG. 2  is a close-up section of the lens of  FIG. 1 . 
         FIG. 3  an image of a nanostructure assembly according to one embodiment. 
         FIGS. 4-5  depict the formation of the nanostructure assembly of  FIG. 3 . 
         FIG. 6  is a fabrication set-up for forming the nanostructure assembly of  FIG. 3 . 
         FIG. 7  is a chart describing the refractive index of assemblies formed at various evaporation angles. 
         FIG. 8  is a chart describing the reflectance of the nanostructure assembly of  FIG. 3 . 
         FIG. 9  is a top view of a nanostructure assembly according to another embodiment of the disclosure. 
         FIG. 10  is a side view of the nanostructure assembly of  FIG. 9 . 
         FIG. 11  is still another nanostructure assembly according to another embodiment of the disclosure. 
         FIG. 12  is still another nanostructure assembly according to another embodiment of the disclosure. 
         FIG. 13  depicts a portion of multi-layer film that can be formed with one of the nanostructure assemblies of the present disclosure. 
         FIGS. 14 and 15  depict examples of layers that can be used in the multi-layer film of  FIG. 13 . 
         FIG. 16  is a front view of an intraocular lens provided with an anti-reflective assembly. 
         FIG. 17  is a side view of the intraocular lens of  FIG. 12 . 
     
    
    
     DETAILED DESCRIPTION 
     For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments, or examples, illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended. Any alterations and further modifications in the described embodiments, and any further applications of the principles of the invention as described herein are contemplated as would normally occur to one skilled in the art to which the invention relates. 
       FIGS. 1 and 2  show an ophthalmic lens  10  with a lens body  12  with a curved surface  14 . An nanostructure formation or assembly  16  is formed on the curved surface  14  of the lens body  12 . As shown in the detailed view of  FIG. 2 , the nanostructure assembly  16  comprises a substrate  18  upon which nanostructures  20  are formed. The nanostructures  20  include protrusions  22  and interstices or spacings  24 . The shape, size, angle, density, and material properties of the nanostructures may be designed to modify the effective refractive index of the lens  10 , and thereby modify the reflectance of the lens. Designing the nanostructures with interstices to create a porous assembly  16  may result in the assembly having a lower refractive index than the material would have if deposited as a uniform layer. The porous assembly created by the nanostructures may further serve to reduce surface reflection, reduce surface scattering, improve biological tissue interaction, improve surface lubrication, and reduce or prevent posterior capsular opacification. As will be described in greater detail below, in some embodiments, multiple layers of the porous assembly  16  may be used increase reflectivity or create a multi-layer mirror. 
     In this embodiment, the protrusions  22  have an approximate height H between 100 and 200 nm and an approximate width W between 25 and 50 nm. The spacings  24  between the protrusions  22  have an approximate width S between 10 and 30 nm. It is understood that these dimensions are meant to be examples and dimensions greater or less than the dimensions listed may also be suitable. Through a combination of the shape, size, angle, density, and material properties of protrusions  22  and the shape, size, and density of the interstices  24 , the assembly  16  may be formed to have a lower index of refraction than the lens body  12 , thus reducing the amount of reflection caused by the lens  10  compared to the lens body  12  without the assembly  16 . In at least one embodiment, the index of refraction of the assembly  16  may be less than 1.4 where the index of the unmodified lens body would otherwise range from about 1.52 to about 1.60. In other embodiments, the refractive index of the assembly may be between approximately 1.30 and 1.60. 
     The nanostructures may serve to reduce the reflectivity of the lens as compared to a lens without the nanostructures. For example intra ocular lenses in an aqueous environment may have a reflectivity of approximately 0.6%. A contact lens in an air environment may have a reflectivity approximately in the range of 2.5 to 5.5%. The incorporation of nanostructures, such as those described above and below, may serve to reduce the reflectivity. 
     In this embodiment, the anti-reflective assembly is shown to cover the entire curved surface  14 , but in alternative embodiments, the anti-reflective assembly may be applied to discrete regions and omitted in other regions. In this embodiment, the curved surface is a convex surface, but in alternative embodiments, the surface of the lens body that receives the anti-reflective assembly may be convex, flat, or have a varied shape. Also in alternative embodiments, the anti-reflective assembly may be formed inside the lens body. For the purposes of this disclosure, the term “anti-reflective” may mean “non-reflective” or any level of reflectivity less than the lens body would have alone. In some alternative embodiments, the substrate may be the lens body itself, but in other embodiments, the substrate may be a separate material that is applied to the lens body. 
     Referring now to  FIG. 3 , in one embodiment, the assembly  16  may be a nanoporous film  29  with a substrate  30  from which generally discrete rods  32  extend. The substrate may be, for example, a lens body. The rods  32  are separated by spacings or pores  34 . The rods may have a height H between approximately 100 and 200 nm and a width W between approximately 25 and 50 nm. The pores may have a width S of approximately 20 nm. 
     The nanoporous film of this embodiment may be fabricated with controllable size ranges using any of a variety of techniques including physical vapor deposition, thermal evaporation, chemical vapor deposition, or etching. Suitable methods of physical vapor deposition may be performed by sputtering or energetic electron beam (E-beam evaporation). Suitable methods of chemical vapor deposition may include plasma enhanced chemical vapor deposition (PECVD). The rods may be formed from any of a variety of materials including dielectrics, metals, polymers, and organic materials. Silicon dioxide (SiO 2 ) is an example of a material that may be suitable. 
       FIGS. 4-5  illustrate an example of a suitable oblique angle evaporation process for fabricating a nanoporous film of the type depicted in  FIG. 3 . As shown in  FIG. 4 , vapor flux  40  is applied at a vapor incident angle θ A  relative to an imaginary line  41  extending perpendicular to a substrate  42 . As the vapor flux  40  is deposited, rods  44  are grown. The growing rods  44  produce shadow regions  46  where the vapor flux cannot be deposited. These regions  46  form the pores  48  between the rods  44 . The porosity can be adjusted by adjusting the incident angle θ A  of the vapor flux. The process may directly modify the lens body substrate or the process may be performed on a separate substrate and later adhered to the lens body. 
     As shown in  FIG. 6 , oblique angle e-beam evaporation is one method that may be used for oblique angle deposition. A substrate  50  may be positioned at an angle θ B  relative to a line L that is parallel to a crucible  52  of source material  54 . SiO 2  may be a suitable source material. A filament  56  may be heated until it emits an electron beam that acts upon the source material to create a vapor  58  that becomes deposited on the substrate  50  in the form of rods as shown in  FIG. 3 . 
     The formed nanoporous film will generally have a refractive index less than the deposited material would have if applied in a uniform and polished layer because the air gaps provided by the pores serve to lower the effective refractive index of the film. By varying the deposition angle, the porosity of the film and therefore the refractive index of the film can be selected and adjusted almost continuously. Thus, the refractive indices of the anti-reflective assemblies formed with this process are tunable in the fabrication process. 
       FIG. 7  depicts experimental data that shows the influence that e-beam evaporation angle has on SiO 2  film fabricated using the above described technique. Each of the curves  70 - 75  represent the refractive index of SiO 2  film fabricated at different e-beam evaporation angles and at wavelengths ranging from 400 to 900 nm. Curve  70  is based upon a 60° evaporation angle. Curve  71  is based upon a 70°evaporation angle. Curve  72  is based upon a 75° evaporation angle. Curve  73  is based upon an 80° evaporation angle. Curve  74  is based upon a 85° evaporation angle. Curve  75  is based upon a 90° evaporation angle. As shown, when the angle between the source material plane and the substrate plane is approximately 80°, the refractive index of the film ranges from approximately 1.17 and 1.13. With larger evaporation angles, the refractive index decreases and with smaller evaporation angles, the refractive index increases. 
     The described technique may be used to create a single level of nanostructures, however in alternative embodiments, a closure layer may be deposited over the formed rods and a second level of rods may be formed on top of the first level. In this way, multilayer structures with even more varying refractive indices may be formed. 
       FIG. 8  shows the calculated reflectance performance of two layers of SiO 2  nanoporous film fabricated using the methods described above. The two layer SiO 2  assembly or coating includes a 145 nm SiO 2  nanoporous layer (n=1.27) followed by a 223 nm SiO 2  nanoporous layer (n=1.05). The reflectance at a wavelength of 633 nm is less than 0.2% for angles up to 70° and less than 12% up to 80°. Similar performance may be maintained for a spectral range between 400 and 800 nm. Reflectance without the SiO 2  nanoporous assembly is also shown. Curve  80  represents the reflectance of a transverse electric (TE) beam with no anti-reflective assembly, and curve  81  represents the reflectance of a transverse magnetic (TM) beam with no anti-reflective assembly. Curve  82  represents the reflectance of a transverse electric (TE) beam with the two layer anti-reflective assembly described above. Curve  83  represents the reflectance of a transverse magnetic (TM) beam with the two layer anti-reflective assembly described above. The chart of  FIG. 8  shows that the reflectance for both TE and TM is nearly zero at incident angles up to 70°, with the use of the anti-reflective assembly. Adding this type of broadband and large acceptance angle anti-reflective coating can reduce undesired reflection and scattering. 
     Referring now to  FIGS. 9 and 10 , in another embodiment, the anti-reflective assembly  16  may be a “moth-eye” structured assembly  90  with periodically repeating protrusions  92  and spacings  94 . The assembly  90  is termed “moth-eye” because the structure is a biomimetic configuration that simulates the structure of a moth eye. The protrusions may be semispherical, conical, pyramidal, or other shape that provides a generally tapered effect. The period of the array is the distance P between the tallest points of adjacent protrusions. Although the period P may vary between adjacent protrusions, it is generally much smaller that the operating wavelength of the lens. The height H of the protrusions is also generally smaller than the operating wavelength of the lens. The effect is a gradient index distribution profile that varies between the index of the surrounding medium and the index of the substrate. Effective medium theory can be applied to calculate the average refractive index of the assembly. The gradient index profile design can be used to create a broad band and large acceptance angle anti-reflective layer. 
     To fabricate the moth-eye structured film, a mold is first fabricated with densely packed nano-spheres or other nano-particles suspended on a silicon substrate. A polydimethylsiloxane (PDMS) mold is cast and may be used for subsequent stamping and replication to mass produce the moth-eye film  90 . The stamping and replication may be applied either to a lens directly or to a material that may be applied to the lens. As with the embodiment of  FIG. 3 , the moth-eye assembly  90  has an effective lower refractive index than the unmodified lens body. Thus, the reflectivity of the lens is reduced compared to the unmodified lens body. 
     Referring now to  FIG. 11 , in another embodiment, the nanostructure assembly  16  may be a grating structure  100  with elongated protrusions  102  and spacings  104  formed in a repeating pattern on a substrate  106 . The protrusions may have a height H and a period P that are generally much smaller that the operating wavelength of the lens. The grating structure  100  may function as an anti-reflective coating. It may also function to couple incident light into guided modes by deflecting or refracting light in desired directions. 
     To fabricate the grating structure  100 , one suitable technique that may be utilized is ultraviolet (UV) interference lithography. This technique may fabricate gratings over large surfaces, such as a lens, and is suitable for use on curved surfaces due to its large depth of focus. Using interference lithography, a mold, made of silicon or other material suitable for mass production, is used for subsequent stamping and replication either of a lens directly or of a material that may be applied to the lens. As with the embodiment of  FIG. 3 , the grating structure  100  has an effective lower refractive index than the unmodified lens body. Thus, the reflectivity of the lens is reduced compared to the unmodified lens body. 
     Referring now to  FIG. 12 , in another embodiment, the assembly  16  may be similar the nanoporous film  29  described above, but rather than linear rods, a plurality of helical rods  110  extend from the substrate. Helical rods may be formed by rotating the substrate during the formation process, such as an oblique angle deposition process. Because the in-plane orientation of the rods  110  change continuously as the film grows, the film can be designed for reflective or anti-reflective applications. 
     Referring now to  FIG. 13 , in an alternative embodiment, layers of nanostructure assemblies  120 , of any of the types described above, may be arranged to effect a highly reflective multi-layer film  119 . In this embodiment, each film layer  122 - 128  includes a nanostructure assembly  120 . The layers  122 - 128  are birefingent and when arranged as described below form a highly reflective multi-layer film having giant birefingent optic (GBO) properties. For example, layers  122  and  126  have nanostructures oriented in the YZ plane.  FIG. 14  provides an example of a layer  130  with nanostructure gratings  134  oriented in the YZ plane.  FIG. 15  provides an example of a layer  140  with nanorods  144  oriented in the YZ plane. Layers  124  and  128  of the film  119  have nanostructures oriented in the XZ plane.  FIG. 14  provides an example of a layer  132  with nanostructure gratings  136  oriented in the XZ plane.  FIG. 15  provides an example of a layer  142  with nanorods  146  oriented in the XZ plane. Although discretely layered films have been described, in alternative embodiments, helical rods, such as those described above for  FIG. 12 , may be used to effect continuously changing in-plane orientation. The helical rods described above for  FIG. 12  may also be used to effectively create a continuously changing in-plane orientation. 
     Highly reflective films formed using nanostructures may be used in applications that utilize mirrored surfaces or films. For example, mirrored optical implants, such as telescopic intraocular implants, may utilize mirrored components to effect reflection and focusing of light. U.S. Pat. No. 7,842,086, which is incorporated by reference herein in its entirety, describes mirrored intraocular implants that may suitable for use with the above described highly reflective films. In one embodiment, such an intraocular implant includes an implant body with a plurality of mirrors that receive light from a scene and focus the light onto the retina. At least one of the mirrors includes a surface that is made highly reflective through the use of the previously described nanostructure reflective films. Generally, the reflective surfaces have a reflectivity of approximately 25% or more. 
     Referring now to  FIGS. 16 and 17 , an intraocular lens  150  is one type of ophthalmic lens that may be improved using any of the above described nanostructure assemblies  16 . The intraocular lens  150  has a lens body  152  from which a pair of lens retaining haptics  154  extend. As shown more clearly in  FIG. 17 , a nanostructure assembly  156 , of any of the types described above, may cover the surfaces of the lens body  152 . It may, alternatively, be desirable to also cover the haptics or only cover a portion of the lens body. A suitable intraocular lens may have a lens body formed of silicone or of a polymer such as ACRYSOF® (trademark of Alcon, Ft. Worth, Tex.). 
     For intraocular lenses and other ophthalmic lenses that directly contact or are implanted in the eye, biocompatibility is important to the functionality of the lens. The variegated surfaces of the above described anti-reflective assemblies may allow for microlubrication and the movement and channeling of beneficial fluid into contact with the surrounding biologic tissue. For example, an intraocular lens interacts with the aqueous humor of the eye and the use of the assemblies  16  may permit extended wear while also reducing reflectivity of the lens. 
     Although several selected embodiments have been illustrated and described in detail, it will be understood that they are exemplary, and that a variety of substitutions and alterations are possible without departing from the spirit and scope of the present invention, as defined by the following claims.