Abstract:
An optical zone for a lens has a center optical axis. A first region of the optical zone includes a first optical curve having a first optical axis that is collinear with the center optical axis. A plurality of secondary regions is formed within the first region. Each of the secondary regions has a respective secondary optical curve with a corresponding secondary optical axis. Each secondary optical axis is collinear with the first optical axis. Each of the secondary optical curves is decentered relative to the first optical curve.

Description:
FIELD OF THE INVENTION 
     The present invention relates to contact lenses. More particularly, the present invention relates to a contact lens that combines the desirable characteristics of simultaneous and translating bifocal and/or multifocal lenses, and a method of manufacturing such a lens. 
     BACKGROUND OF THE INVENTION 
       FIG. 1  (not drawn to scale) shows an exemplary conventional bifocal contact lens  10  having an optical zone  12 . Optical zone  12  is comprised of concentric zones of alternating near viewing regions  14  and distance viewing regions  16 . When viewing a distant image through optical zone  12 , the image appears focused and clear when viewed through distance regions  16  but out of focus when viewed though near regions  14 . A similar effect occurs when viewing a near object. In effect, the wearer experiences an undesirable effect referred to as simultaneous vision in which the image appears in focus but is surrounded by an out-of-focus halo. 
     Near viewing regions  14  and distance viewing regions  16  are continuous around optical zone  12 . Thus, lens  10  may rotate freely in the eye and no ballasting techniques are required to maintain orientation of lens  10 . The ability of lens  10  to freely rotate provides for more efficient flushing of the surface of lens  10  with tears when the wearer thereof blinks. 
     Thus, although conventional bifocal contact lens  10  is efficiently flushed with tears, the wearer may experience undesirable simultaneous vision. 
       FIG. 2  (not drawn to scale) shows an exemplary conventional translating bifocal contact lens  30  having an optical zone  32 . Optical zone  32  is divided into a superior region  34  that is optimized for distance vision and an inferior region  36  that is optimized for near vision. When the wearer looks down to read or view a near object his or her pupil is disposed mostly in the inferior or near-viewing region  36 . When the wearer looks forward at a distant object the pupil is mostly disposed in the superior or distance region  34 . Thus, translating bifocal contact lens  30  reduces the occurrence of simultaneous vision. The translating bifocal is a popular lens configuration because it enables the wearer to shift the amount of light to the pupil and provides better visual quality than simultaneous bifocal contact lenses. 
     However, inferior or near region  36  generally has a steeper curve than superior or distance region  34 . In order to compensate for that relatively steep curve and maintain a generally round shape, translating bifocal contact lens  30  is typically thicker than other contact lenses and has a large step  38  (i.e., a sudden increase and/or decrease in thickness) between inferior/near region  36  and superior/distance region  34  (which is exaggerated as shown in  FIG. 2 ). The relative thickness of translating bifocal contact lens  30  and the large step  38  between the inferior/near region  36  and superior/distance region  34  thereof may cause discomfort to some wearers. 
     Furthermore, ballasting techniques (not shown) must be used to orient translating bifocal contact lens  30  such that near objects are viewed through the inferior/near region  36  and distant objects are viewed through the superior/distance region  34 . Ballasting techniques reduce the efficiency with which a lens is flushed. The extra thickness of these lenses and the required ballasting techniques reduce the oxygen transfer to the surface of the eye and could lead to an increased risk of corneal edema. 
     Thus, although reducing simultaneous vision and providing better visual quality than simultaneous bifocal contact lens  10 , translating bifocal contact lens  30  reduces oxygen transfer to the eye, is flushed less efficiently, and may be uncomfortable to some wearers. 
     Therefore, what is needed in the art is a multifocal contact lens that reduces the occurrence of simultaneous vision and which provides improved visual quality without reducing oxygen transfer to the eye. 
     Furthermore, what is needed in the art is a multifocal contact lens that reduces the occurrence of simultaneous vision and which provides improved visual quality while still providing for relatively efficient flushing of the lens. 
     Moreover, what is needed in the art is a multifocal contact lens that reduces the occurrence of simultaneous vision and which provides improved visual quality without requiring large steps between visual regions which may cause wearer discomfort. 
     Lastly, what is needed in the art is a multifocal contact lens that combines the desirable qualities, characteristics, and properties of simultaneous vision contact lenses with those of translating vision contact lenses. 
     SUMMARY OF THE INVENTION 
     The present invention provides a contact lens and method for making same. Further, the present invention provides an optical zone for a contact lens, and a method for making that optical zone. 
     The invention comprises, in one form thereof, an optical zone having a center optical axis. A first region of the optical zone includes a first optical curve having a first optical axis that is collinear with the center optical axis. A plurality of secondary regions are formed within the first region. Each of the secondary regions has a respective secondary optical curve with a corresponding secondary optical axis. Each secondary optical axis is collinear with the first optical axis. Each of the secondary optical curves is decentered relative to the first optical curve. 
     An advantage of the lens of the present invention is that the occurrence of simultaneous vision is reduced and improved visual quality is provided without a substantial reduction in the amount of oxygen transferred to the eye. 
     Another advantage of the lens of the present invention is that the occurrence of simultaneous vision is reduced and improved visual quality is provided without substantially reducing the efficiency with which the lens is flushed by tears. 
     Yet another advantage of the contact lens of the present invention is that the occurrence of simultaneous vision is reduced and improved visual quality is provided without requiring large steps between visual regions, thereby reducing discomfort to lens wearers. 
     A still further advantage of the contact lens of the present invention is that the desirable qualities, characteristics, and properties of simultaneous vision contact lenses are combined with those of translating vision contact lenses. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become apparent and be better understood by reference to the following description of one embodiment of the invention in conjunction with the accompanying drawings, wherein: 
         FIGS. 1   a  and  1   b  are front and side views, respectively, of a conventional concentric bifocal contact lens; 
         FIGS. 2   a  and  2   b  are front and side views, respectively, of a conventional translating bifocal contact lens; 
         FIG. 3  is a front view of one embodiment of a multifocal contact lens of the present invention; 
         FIG. 4  is a side profile view of the optical zone of the contact lens of  FIG. 3 ; and 
         FIGS. 5(   a )–( b ) illustrate the process steps for production of the invention. 
     
    
    
     Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate one preferred embodiment of the invention, in one form, and such exemplifications are not to be construed as limiting the scope of the invention in any manner. 
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to  FIGS. 3 and 4 , one embodiment of a contact lens of the present invention is shown. As best shown in  FIG. 4 , lens  50  includes an anterior surface  52  and a posterior surface  54 . Anterior surface  52  includes an optical zone  60  formed therein according to a method to be hereinafter described, and posterior surface  54  is formed to conform to the cornea of a wearer in known fashion. 
     Optical zone  60  includes first region  62 , central zone  63  and secondary regions  64   a ,  64   b ,  64   c ,  64   d ,  64   e . For each region, the optical curve is a sphere. First region  62  is primarily disposed in the superior region of optical zone  60 , and secondary regions  64   a–e  are disposed primarily in the inferior region of optical zone  60 . Secondary regions  64   a–e  are substantially concentric relative to each other. Generally, lens  50  is designed for distance viewing by configuring first region  62  as a distance viewing region. Secondary regions  64   a–e  may be configured as near or intermediate viewing regions, or a combination thereof. Central region  63  can be configured either as a distance, intermediate or near viewing region to thereby optimize lens  52  for distance, intermediate or near viewing, respectively. As shown in  FIGS. 3 and 4 , first region  62  and central region  63  are configured as distance viewing regions, whereas secondary regions  64   a–e  are configured as near viewing regions, and therefore lens  50  is configured as a bifocal lens with a distance-viewing central region. 
     Referring again to  FIG. 4 , lens  50  is shown in profile. First region  62  is formed such that the center of the apical or vertex radius  74  thereof lies along and/or upon optical axis  80 . It should be particularly noted that the center  74  of the apical or vertex radius is hereinafter referred to simply as a center of curvature  74 . However, it is to be understood that the term “center of curvature” is used herein to refer to the center of aspherical as well as spherical surfaces, and that when used in connection with an aspherical surface the term “center of curvature” refers to the center of the apical or vertex radius of that particular surface. 
     Secondary regions  64   a–e  are formed in optical zone  60  of lens  50  such that the centers of curvature thereof, collectively designated  82  in  FIG. 4 , also lie along optical axis  80 . Thus, secondary regions  64   a–e , central region  63  and first region  62  are monocentric with respect to each other, i.e., they share a common optical axis. The monocentricity of first region  62  and secondary regions  64   a–e  reduces the potential that the lens wearer will be subjected to asymmetrical ghost images, and reduces the potential for the patient to be subjected to a “jump” in the viewed image as the contact lens translates on the eye. Adjacent secondary regions  64   a–e  are separated from each other by steps (not referenced) along the superior-inferior meridian having step heights  84 . Step heights  84  are maintained below a predetermined maximum, such as, for example, 10 μm, to minimize wearer discomfort. It should be understood, however, that step height  84  may not be the same for all secondary regions  64   a–e  and that step height  84  will not be constant along junctions between secondary regions  64   a–e , but will remain below the stated maximum. 
     Although the centers of curvature of secondary regions  64   a–e  are shown as one point  82 , one skilled in the art will recognize that the centers of curvature of secondary regions  64   a–e  are actually distinct points that may be slightly spaced apart from each other along optical axis  80  such that center of curvature of secondary region  64   a  is relatively proximate to center of curvature  74  and the center of curvature of secondary region  64   e  is relatively distant from center of curvature  74 . 
     In the embodiment shown, lens  50  is optimized for distance viewing by configuring central region  63  of optical zone  60  as a distance-optimized viewing region. However, it is to be understood that lens  50  can be alternately configured and optimized for near viewing by forming central region  63  of optical zone  60  as a near-optimized viewing region. The ability to form central region  63  of lens  50  as either a near-optimized or distance-optimized region renders lenses according to the present invention appropriate for monovision applications in which the contact lens in one eye is optimized for near vision and the contact lens in the other eye is optimized for distance viewing. 
     In the embodiment shown, lens  50  is configured as a bifocal lens and therefore secondary regions  64   a–e  are each configured with the same or substantially the same optical power. However, it is to be understood that lens  50  can be alternately configured as a multifocal lens by configuring some of secondary regions  64   a–e  as near-range optimized viewing regions and some other of secondary regions  64   a–e  as intermediate-range optimized viewing regions. 
     Referring now to  FIGS. 5(   a ) and  5 ( b ), one embodiment of a method for manufacturing a lens according to the present invention is shown. Lens  50  is molded from silicone, Hydroxyethyl methacrylate (HEMA), or other suitable materials that are biocompatible with the cornea. Generally, a mold tool, preferably constructed of nickel on steel, is machined and anterior molds are made from the machined mold tool. The anterior molds are typically constructed of an injection molded plastic material, such as, for example, polypropylene or polyvinyl chloride. The molds are then used to cast mold contact lenses according to the present invention. 
     Mold tool  90  is formed from a material blank  94 , such as, for example, a blank of steel or other appropriately hard material, that is machined by diamond cutting tool  96  into the desired shape of lens  50 . Cutting tool  96  is mounted on an oscillating and/or reciprocating tool holder or tool post assembly  98 . Generally, tool holder  98  is translatable in the direction of the x-axis, and is capable of precise and very rapid axial oscillation and/or reciprocation in the z-axis direction. One embodiment of such a tool holder is more fully described in U.S. Pat. No. 5,718,154, entitled RECIPROCATING TOOL HOLDER ASSEMBLY, the disclosure of which is incorporated herein by reference. 
     The material blank  94  from which the mold is to be formed is mounted on work piece collet  102  that is rotatable in direction θ. Cutting tool  96  is then controlled, such as, for example, by numerical or computer control, and is simultaneously translated along the x-axis and reciprocally adjusted along the z-axis to create the desired shape of lens  50 . 
     More particularly, upper surface  110  of material blank  94  is cut to form surface  112  ( FIG. 5   a ), which corresponds to anterior surface  52  of lens  50 . During the same or a subsequent pass of cutting tool  96 , upper surface  110  of material blank  94  is also cut to create surface  114  that conforms to the desired curve of first region  62  of optical zone  60  and which has a center of curvature  116  that is coincident with central or optical axis  80  ( FIG. 5   a ). Thereafter, surface  114  is further cut to create surfaces  114   a ,  114   b  and  114   c  ( FIG. 5   b ) that correspond to particular secondary regions  64   a–e  of optical zone  60 . If desired, additional surfaces corresponding to additional secondary regions  64   a–e  are also formed as described above. 
     To create surfaces  114   a ,  114   b  and  114   c  cutting tool  96  (via tool holder  98 ) is translated from the outside of surface  114  toward the inside thereof, i.e., along the x-axis. As tool holder  98  and, thereby, cutting tool  96  are translated in the direction of the x-axis, cutting tool  98  and tool holder  96  are also oscillated and/or reciprocated in the z-axis direction to thereby cut surfaces  114   a ,  114   b , and  114   c . Cutting tool  96  is lowered into contact with surface  114  at a location corresponding to one of tips T ( FIG. 3 ) of secondary regions  64   a–e  and is raised from surface  114  at a second location corresponding to the opposite tip T in that same secondary region. Surfaces  114   a–c  appear as ramp-like surfaces when mold  90  is viewed in profile and/or cross-section (see  FIG. 5   b ), and correspond to secondary regions  64   a–e . The apparent tilt of surfaces  114   a ,  114   b , and  114   c  is provided by the reciprocation and/or oscillation of cutting tool  96  by tool holder  98 , which essentially produces a titled surface without the need to tilt either the cutting tool  96 , tool holder  98 , collet  102  and/or mold tool  90 . 
     The equation that controls the curve of the surfaces  114   a ,  114   b  and  114   c  is: 
     
       
         
           
             z 
             = 
             
               
                 
                   
                     x 
                     2 
                   
                   / 
                   R 
                 
                 
                   1 
                   + 
                   
                     
                       ( 
                       
                         1 
                         - 
                         
                           ( 
                           
                             
                               x 
                               2 
                             
                             / 
                             
                               R 
                               2 
                             
                           
                           ) 
                         
                       
                       ) 
                     
                     
                       1 
                       / 
                       2 
                     
                   
                 
               
               + 
               
                 a 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 sin 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 θ 
               
             
           
         
       
     
     Where, x 2 /R is the term for the curve of the region, R is the apical radius of the curve, k is the conic constant of the curve, and
 
1+(1−(x 2 /R 2 )) 1/2 
 
wherein θ is the angular orientation of mold tool  90  relative to central axis  80  ( FIG. 5   a–b ).
 
     The surfaces  114   a ,  114   b  and  114   c  have a common optical axis that corresponds to and is co-axial relative to optical axis  80  of lens  50 . The surfaces  114   a ,  114   b ,  114   c , are cut into the material blank  94  in such a manner so as to maintain a maximum step height  84  of 10 μm. Cutting tool  96  is then raised to the edge of the step and a new surface (not shown) corresponding to one of secondary regions  64   a–e  is cut into material blank  94 . This process is repeated until the number of surfaces  114   a–c  created in material blank  94  correspond to the desired number of secondary regions  64   a–e  to be included in lens  50 . Subsequent process steps for mounting the lens to appropriate ballasting systems are conventional and need not be separately illustrated. The formation of the posterior portion  54  of lens  50  is also conventional and is therefore not shown in detail. 
     Once mold tool  90  is completely formed, anterior molds are constructed by conventional injection molding techniques. A plastic material, such as, for example, polypropylene or polyvinyl chloride, is injection molded to the shape of the finished upper or machined surface  114  of mold tool  90 . The molds are then used in a known manner to cast mold contact lenses according to the present invention. 
     In the embodiment shown, a mold tool is formed which is used to form a mold that, in turn, is used to cast mold contact lenses according to the present invention. However, it is to be understood that the method for forming the contact lenses of the present invention can be alternately performed, such as, for example, directly forming the optical zone of a contact lens of the present invention without the use of a mold tool and/or mold. In such an embodiment, the various features of optical zone  60  are formed, such as, for example, by diamond-turning, chemical etching and/or laser cutting, directly upon the appropriate portion of anterior surface  52  of contact lens  50 . 
     It is to be further noted that the intermediate injection molds formed by mold tool  90  create the negative images of the various features and/or surfaces, including surfaces  114   a ,  114   b ,  114   c  and  114  of mold tool  90 , that correspond to the features and/or surfaces of optical zone  60 . 
     It should be understood that the locations of the tips T ( FIG. 3 ) of secondary regions  64   a–e  within first region  62  can be alternately configured to adjust the optimization of lens  50 . More particularly, and as an example, raising tips T higher into first region  62  and/or bringing tips T closer together renders lens  50  more near optimized when secondary regions  64   a–e  are near-viewing optimized regions. Conversely, and as a second example, lowering tips T within first region  62  and/or spacing tips T further apart renders lens  50  more distance optimized. 
     While this invention has been described as having a preferred design, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the present invention using the general principles disclosed herein. Further, this application is intended to cover such departures from the present disclosure as come within the known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.