Abstract:
Ophthalmic lenses, for example, intraocular lenses, contact lenses, corneal implant lenses and the like, have multifocal characteristics which provide beneficial reductions in at least the perception of one or more night time visual symptoms such as “halos”, and “glare or flare”.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to ophthalmic lenses. More particularly, the invention relates to multifocal ophthalmic lenses for use in or on the eye, such as intraocular lenses, contact lenses, corneal implant lenses and the like. 
     The general construction of a multifocal ophthalmic lens is known in the art. For example, Portney U.S. Pat. No. 5,225,858, which is incorporated herein by reference, discloses a multifocal ophthalmic lens including a central zone circumscribed by multiple concentric, annular zones. This patent discloses multifocal lenses having good image quality and light intensity for near objects. The multifocal lens of this patent includes zones for near vision correction in which the vision correction power substantially constant throughout. 
     Although multifocal lenses of this type provide very effective vision correction, further enhancements would be advantageous. 
     For example, experience with multifocal lenses as described above has identified two general types of night time visual symptoms referred to as “glare or flare” and “halos”. The “glare or flare” symptom manifests itself as radial lines radiating from distant small bright objects at night. The “halos” symptom generally manifest itself as diffuse shadows surrounding distant small bright objects, again noticed at night. These visual symptoms are likely caused by out of focus light passing through the near zone or zones of the lenses. 
     SUMMARY OF THE INVENTION 
     New ophthalmic lenses which address one or more the above-noted symptoms have been discovered. The present lenses take advantage of the discovery that one or more modifications to the surface of a multifocal lens can provide a beneficial reduction in at least the perception of one or more of the above-noted night time visual symptoms. These modifications can be very conveniently and effectively implemented substantially without increasing the cost or difficulty of manufacturing such lenses. The present lenses preferably reduce the size of the major halo which may be apparent when viewing distant objects at night time. In addition, the central zone of the present lenses preferably is modified to change the vision correction power above the baseline diopter power toward the center of the lens to provide an increase in ray density which enhances near image performance. In summary, the present modification or modifications to the multifocal lenses provide additional advantages in already effective multifocal ophthalmic lenses. 
     In one broad aspect of the present invention, an ophthalmical lens having a baseline diopter power for far vision correction is provided. The ophthalmic lens comprises a near zone, preferably an annular near zone, including an inner region, having a substantially constant vision correction power greater than the baseline diopter power and having vision correction powers greater than the baseline diopter power which reduce the size, that is the apparent or perceived size, of a halo caused by passing light to the near zone relative to the halo caused by passing light to a similar near zone of a substantially identical lens in which the similar near power has a constant vision correction power throughout. 
     Preferably, the near zone has a highest vision correction power, which may be the substantially constant vision correction power of the inner region, and includes an outer region located outwardly of the inner region. This outer region has vision correction powers which are progressively reduced from the highest vision correction power of the near zone to a reduced near vision correction power which is between about 50% and about 85% of the highest vision correction power of the near zone. The inner region has an innermost end and the outer region has an outermost end. The radial width of the inner region more preferably is in the range of about 30% to about 85% of the radial distance between the innermost end of the inner region and the outermost end of the outer region. 
     Without wishing to limit the invention to any particular theory of operation, it is believed that the reduction of the vision correction power in the outer region of the near zone is effective to reduce the size of the most apparent or most perceived halo around small light sources viewed from a distance, for example, at night time. 
     In one very useful embodiment, the present ophthalmic lenses further comprise an additional near zone, preferably an annular additional near zone, located outwardly of, and preferably circumscribing, the near zone and having vision correction powers greater than the baseline diopter power. The additional near zone preferably includes vision correction powers which diffuse, or increase the apparent or perceived size of, a halo caused by passing light to the additional near zone relative to the halo caused by passing light to a similar additional near zone of a substantially identical lens in which the similar additional near zone has a constant vision correction power throughout. In one very useful embodiment, the width of the additional near zone is less than about 40% of the radial width of the near zone. The additional near zone has an inner end and an outer end and vision correction powers which preferably increase progressively from the inner end to the outer end. 
     The present ophthalmic lenses preferably reduce the size of the halo resulting from passing light to the near zone and increase the size of the halo resulting from passing light to the additional near zone. The overall effect of the near zone, and preferably the additional near zone, of the present ophthalmic lenses preferably is to effectively and advantageously reduce the apparent or perceived “halo” visual symptom, and more preferably the “glare or flare” visual symptom, which have been noted during use of previous multifocal lenses. 
     The present ophthalmic lenses preferably are selected from intraocular lenses, contact lenses, corneal implant lenses and the like. 
     The present ophthalmic lenses may, and preferably do, include a central zone having a vision correction power greater than the baseline diopter power. The near zone is located outwardly of, and preferably circumscribes, the central zone. 
     In an additional broad aspect of the present invention, ophthalmic lenses having a baseline diopter power for far vision correction are provided which comprise a central zone including a center region, an intermediate region, and an outer region. The center region has a vision correction power, for example, substantially equal to the baseline diopter power although the center region can have a vision correction power which is less than or greater than the baseline diopter power. The intermediate region is located outwardly of the center region and has a vision correction power which is the highest vision correction power in the central zone. The outer region is located outwardly of the intermediate region and has a vision correction power equal to the vision correction power of the center region. The highest vision correction power in the central zone is closer, in terms of radial distance, to the vision correction power of the center region than to the vision correction power of the outer region equal to the vision correction power of the center region. 
     Without wishing to limit the invention to any particular theory of operation, it is believed that the modification in which the highest vision correction power of the central zone is closer to the vision correction power of the center region increases the ray density closer to the center or optical axis of the lens, which enhances near image performance. 
     The vision correction powers of the central zone preferably vary progressively. The highest vision correction power in the central zone preferably is located about 40% or less, more preferably about 35% or less, of the distance, for example, the radial distance, between the vision correction power of the center region and the vision correction of the outer region equal to the vision correction power of the center region. 
     In one very useful embodiment, the ophthalmic lenses preferably further comprise a first outer zone located outwardly of the central zone and having a vision correction power less than the baseline diopter power; and a second outer zone located outwardly of the first outer zone and having a vision correction power greater than the baseline diopter power. Preferably, the intermediate region, the outer region, the first outer zone and the second outer zone are annular and circumscribe the center region, the intermediate region, the outer region and the first outer zone, respectively. 
     The second outer zone preferably includes vision correction powers which reduce the size of a halo caused by passing light to the second outer zone relative to the halo caused by passing light to a similar second outer zone of a substantially identical lens in which the similar second outer zone has a constant vision correction power throughout. The second outer zone preferably has inner and outer regions and other characteristics similar to those of the near zone described elsewhere herein. 
     The present ophthalmic lenses preferably include a third outer zone located outwardly of the second outer zone and having a vision correction power greater than the baseline diopter power. This third outer zone preferably includes vision correction powers which diffuse a halo caused by passing light through the third outer zone relative to the halo caused by passing light to a similar third outer zone of a substantially identical lens in which the similar third outer zone has a width which preferably is less than about 40% of the width of the second outer zone. The third outer zone preferably has an inner end and an outer end and vision correction powers which increase progressively from the inner end to the outer end. 
     In a very useful embodiment, the ophthalmic lenses of the present invention further comprise a fourth outer zone located outwardly of the second outer zone and inwardly of the third outer zone and having vision correction powers less than the baseline diopter power. This fourth outer zone preferably has an inner region having a vision correction power, an intermediate region located outwardly of the inner region and an outer region located outwardly of the intermediate region. The intermediate region has a vision correction power which is increased relative to the vision correction power of the inner region and is the highest vision correction power in the intermediate zone and an outermost diopter power equal to the vision correction power of the inner region. The outer region has a vision correction power which is the lowest vision correction power of the fourth outer zone. The highest vision correction power of the fourth outer zone is located closer, that is radially closer, to the vision correction power of the inner region than to the outermost vision correction power of the intermediate region. This preferred fourth outer zone configuration provides the present lenses with enhanced far vision performance, particularly in dim light and/or at night time. 
     The first, second and third outer zones preferably are annular and the first annular zone circumscribes the central zone, the second outer zone circumscribes the first outer zone and the third outer zone circumscribes the second outer zone. In the event the fourth outer zone is included, the fourth outer zone preferably is annular and circumscribes the second outer zone and is circumscribed by the third outer zone. 
     The portions of the present lenses between the various zones of differing vision correction powers can be referred to as transition portions or zones. Such transition portions or zones can provide for an abrupt or “step function” change in vision correction power. Preferably, however, the transition portions or zones provide for a more gradual or progressive change in vision correction power. 
     The desired powers for the present lenses can be provided in various different ways, including the use of refracting surfaces. In one preferred embodiment, the lens has anterior and posterior surfaces, at least one of which is shaped to provide the desired vision correction powers. With this construction, the progressive portion or portions of the lens are aspheric, and although the regions of the lens of constant power can be spheric if desired, preferably they are also aspheric. In a preferred construction, the lenses of the invention are aspheric throughout the annular zones and the central zone, and this provides certain advantages in designing the lens and also can be used to compensate for spherical aberrations for far vision portions and near vision portions of the lens. 
     For a contact lens, it is preferred to shape the posterior surface to fit the curvature of the patient&#39;s eye and to configure the anterior surface to provide the desired correction. 
     Each and every feature described herein, and each and every combination of two or more of such features are included with the scope of the present invention provided that the features included in any such combination are not mutually inconsistent. 
     These and other aspects of the present invention are apparent in the following detailed description and claims particularly when considered in conjunction with the accompanying drawings in which like parts bear like reference numerals. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a plan view of a multifocal intraocular lens embodying features of this invention. 
     FIG. 2 is a side elevation view of the IOL shown in FIG.  1 . 
     FIG. 3 is a side elevation view of a corneal contact lens embodying features of the present invention. 
     FIG. 3A is a plan view of the corneal contact lens shown in FIG.  3 . 
     FIG. 4 is a plot of the power of an optic versus distance from the optical axis for a prior art multifocal intraocular lens. 
     FIG. 5 is a plot of the power of the optic versus distance from the optical axis of the multifocal intraocular lens shown in FIG.  1 . 
     FIG. 6 is a schematic illustration of viewing a distant object during night time conditions using the intraocular lens shown in FIG.  1 . 
     FIG. 7 is a schematic illustration of viewing a distant object during night time conditions using the prior art intraocular lens of FIG.  4 . 
     FIG. 8 is a plot of the power of the contact lens shown in FIGS. 3 and 3A versus distance from the optical axis of the lens. 
     FIG. 9 is a plot of the power of an optic of an alternate intraocular lens in accordance with the present invention versus distance from the optical axis of the optics. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 1 and 2 show an intraocular lens  11  which comprises a circular optic  13  and fixation members  15  and  17 . The optic  13  may be constructed of rigid biocompatible materials, such as polymehtylmethacrylate (PMMA), or flexible, deformable materials, such as silicones, deformable acrylic polymeric materials, hydrogels and the like which enable the optic to be rolled or folded for insertion through a small incision into the eye. 
     In this embodiment, the fixation members  15  and  17  are fine hair-like strands or filaments which are attached to the optic  13  using conventional techniques. The fixation members  15  and  17  may be constructed of a suitable polymeric material, such as PMMA or polypropylene. Alternatively, the fixation members  15  and  17  may be integral with the optic  13 . The optic  13  and the fixation members  15  and  17  may be of any desired configuration, and the configurations illustrated are purely illustrative. 
     The optic  13  has a central zone  18 , inner and outer annular near zones  20  and  22  and annular far zones  24  and  26 . In this embodiment, the central zone  18  is circular. The annular zones  20 ≧ 26  circumscribe the central zone  18 , and are concentric and coaxial with the optic  13 . 
     The zones  18 - 26  are used in describing the vision correction power of the optic  13 , and they are arbitrarily defined. Thus, the peripheries of the zones  18 - 26  and the number of zones may be selected as desired. However to facilitate describing the optic  13 , the peripheries of the annular zones  20 - 26  are considered to be the major zero crossings in FIG.  5 . Although the boundaries of the zones  18 - 26  are indicated by phantom lines in FIG. 1, it should be understood that the optic  13  has no such lines in any of its surfaces and that these lines constitute reference lines which define the zones. 
     In the embodiment of FIG. 2, the optic  13  has a convex anterior surface  28  and a planar posterior surface  30 ; however, these configurations are merely illustrative. Although the vision correction power may be placed on either of the surfaces  28  or  30 , in this embodiment, the anterior surface  28  is appropriately shaped to provide the desired vision correction powers. 
     FIG. 5 shows a preferred manner in which the vision correction power of the optic  13  varies from the center or optical axis  32  of the optic to the circular outer periphery  34  of the optic. A preferred power distribution curve for a corneal inlay (corneal inlay lens) may be similar, or identical, to the curve of FIG.  5 . In FIG. 5, the vertical or “Y” axis represents the variation in diopter power of the optic  13  from the baseline or far vision correction power, and the “X” or horizontal axis shows the distance outwardly, the radial distance, from the optical axis  32 , for example, in millimeters. Thus, the zero-diopter or baseline power of FIG. 5 is the power required for far vision for an IOL. The power variation shown in FIG. 5 is applicable to any radial plane passing through the optic axis  32 . In other words, the power at any given radial distance from the optical axis  32  is the same. 
     The central zone  18  extends from the optical axis  32  to a circular periphery  36 , the inner annular far zone  24  is considered as extending from the periphery  36  to a circular periphery  38 , inner annular near zone  20  is considered as extending from the periphery  38  to a circular periphery  40 , the outer annular far zone  26  is considered as extending from the periphery  40  to the circular periphery  42 , and the outer annular near zone  22  is considered as extending from a periphery  42  to a circular periphery  44 . The annular zone  27  extends from the periphery  44  radially outwardly to the outer periphery  34  of the optic  13 . As shown in FIG. 5, the vision correction power crosses the “X” axis or baseline at the peripheries  36 ,  38 ,  40 ,  42  and  44 . 
     As shown in FIG. 5, the vision correction power varies progressively and continuously from the baseline diopter power at the optical axis  32  to an apex  48  and then decreases continuously and progressively from the apex  48  back to the baseline diopter correction at periphery  36 . The apex  48  is closer, in terms of radial distance, to the optical axis  32  than to the periphery  36 . As illustrated, apex  48  is located away from the optical axis  32  about 30% of the total radial distance between the optical axis and the circular periphery  36 . 
     The vision correction power then decreases continuously and progressively to a negative diopter power at a periphery  50 . The negative diopter power at the periphery  50  is of less power than is required for far vision and may be considered as a far, far vision correction power. From the periphery  50 , the vision correction power increases continuously and progressively through the periphery  38  into the inner annular near zone  20 . Of course, the diopters shown on the ordinate in FIG.  5  are merely exemplary, and the actual correction provided will vary with the prescription needs of the patient. 
     Within the inner annular near zone  20 , the vision correction power varies continuously and progressively from the periphery  38  to an inner end  52  of a plateau  54 . The vision correction power at plateau  54  is considered substantially constant although some variation may occur. The plateau  54  has an outer end  56 . At outer end  56 , the vision correction power begins a relatively rapid, in terms of diopters changed per unit of radial distance on the optic  13 , progressive and continuous decrease to point  58  which has a diopter power equal to about 60% of the average diopter power of plateau  54 . The radial width of plateau  54  is equal to about 65% of the radial width, or distance along the Y-axis in FIG. 5, between points  52  and  58 . The vision correction power decreases less rapidly (relative to the rate of power decline between points  56  and  58 ), continuously and progressively from point  58  back to the periphery  40  at the baseline. 
     With continued reference to FIG. 5, the vision correction power from periphery  40  continuously and progressively decreases to point  60  in far zone  26 . From point  60  the vision correction power continuously and progressively increases to apex  62 . The vision correction power then decreases to point  64  at which the vision correction power is equal to that at point  60 . The vision correction power continues to decrease continuously and progressively to point  66  and then increases continuously and progressively to periphery  42 . In far zone  26 , apex  62  is located radially closer to point  60  then to point  64 . In particular, point  62  is located about 30% of the radial distance from point  60  relative to the total radial distance between points  60  and  64 . 
     In the outer annular near zone  22 , the vision correction power increases continuously and progressively from the periphery  42  to the inner end  68  of plateau  70 . The vision correction power at plateau  70 , which is relatively narrow, increases progressively from inner end  68  to outer end  72  of plateau  70 . From the outer end  72 , the vision correction power decreases continuously and progressively to periphery  44 . The vision correction power remains substantially constant at or about the baseline diopter power from periphery  44  to the periphery  34  of optic  13 . 
     The outer near zone  22  includes plateau  70  with progressively increasing optical powers. These increasing powers in plateau  70 , together with the relative narrowness of outer near zone  22  is believed to be effective to diffuse the halo caused by passing light to the outer near zone  22 . 
     By way of comparison and to further illustrate the present invention, FIG. 4 shows the manner in which the vision correction power of a prior art multifocal optic varies from the optical axis of the optic. The zones of the prior art optic in FIG. 4 which correspond to zones of optic  13  in FIG. 5 are identified by the same reference numeral with the addition of the letter “A”. 
     With reference to FIG. 4, the prior art optic, referred to as  13 A, has the same baseline diopter power as does optic  13 . The central zone  18 A extends from the optical axis  32 A to a circular periphery  36 A. The inner annular far zone  24 A is considered as extending from the periphery  26 A to the circular periphery  38 A, the inner annular near zone  20 A is considered as extending from the periphery  38 A to the circular periphery  40 A. The outer annular far zone  26 A is considered as extending from the periphery  40 A to the circular periphery  42 A and the outer annular near zone  22 A is considered as extending from the periphery  42 A to a circular periphery  44 A. As shown in FIG. 4, the vision correction power includes major crossings of the “X” axis or baseline at the peripheries  36 A,  38 A,  40 A,  42 A and  44 A. The crossings of the baseline within outer far zone  26 A are not considered major. 
     Regarding the differences between the vision correction power of optic  13  relative to the vision correction power of optic  13 A, reference is first made to central zones  18  and  18 A. The primary difference between central zones  18  and  18 A relates to the positioning of the apexes  48  and  48 A. In particular, as noted above, apex  48  is located radially closer to the central axis  32  than to periphery  36 . This is contrasted to the positioning of apex  48 A which is located closer to the periphery  36 A than to the central axis  32 A. This difference is believed to provide optic  13  (and IOL  11 ) with enhanced performance in viewing near objects, relative to such performance of optic  13 A. 
     Another substantial difference between optic  13  and optic  13 A relates to inner annular near zones  20  and  20 A. Thus, whereas inner annular near zone  20 A of optic  13 A includes a plateau  54 A which has a substantially constant optical power throughout, plateau  54  is relatively abbreviated and zone  20  includes a region between outer end  56  of plateau  54  and periphery  58  which has a progressively and continuously decreasing optical power. The configuration of inner annular near zone  20  relative to inner annular near zone  20 A is believed to reduce the apparent or perceived size of the halo caused by passing light to the near zone  20  relative to the halo caused by passing light to the zone  20 A. 
     A further substantial distinction between optics  13  and  13 A relates to the variation in vision correction power in outer far zones  26  and  26 A. Thus, whereas zone  26 A is only slightly varied in vision correction power relative to the baseline diopter power. The vision correction power in zone  26  includes substantially reduced optical powers, as described previously. The vision correction power of zone  26  is believed to provide increased vision performance in viewing distant objects in dim light or night time relative to the performance obtained with zone  26 A. 
     An additional substantial difference between optic  13  and optic  13 A relates to the outer annular near zones  22  and  22 A. Specifically, zone  22  is substantially radially more narrow or smaller than is zone  22 A. In addition, zone  22 A has a relatively wide plateau  70 A which includes a substantially constant optical power. In contrast, the plateau  70  of zone  22  includes progressively increasing vision correction powers. Optic  13  with zone  22  diffuses or makes less apparent the halo caused by passing light to zone  22  relative to the halo caused by passing light to zone  22 A of optic  13 A. 
     As a further illustration of the differences between the optic  13  and optic  13 A, reference is made to FIGS. 6 and 7 which are schematic illustrations of a distant object viewed during night time conditions using optic  13 A and optic  13 , respectively. 
     Referring to FIG. 6, viewing the distant object during night time with optic  13 A provides a central image, a halo extending away from the central image and additional random light scattering extending radially beyond the halo. 
     Referring to FIG. 7, viewing the distant object during night time with optic  13  provides a central image of higher quality than in FIG.  6 . In addition, the halo in FIG. 7 extending away from the central image is substantially smaller or reduced in size. Further, substantially no light scattering beyond the halo is apparent radially outwardly from the halo is apparent in FIG.  7 . Overall, the image provided by optic  13  (FIG. 7) is superior to the image provided by optic  13 A (FIG.  6 ). 
     FIGS. 3,  3 A and  8  show a contact lens  111  constructed in accordance with the teachings of this invention. The contact lens  111  is sized and configured to be carried or worn on a surface of the eye. Optically, the contact lens  111  may be substantially identical to the optic  13  of FIGS. 1,  2  and  5  in all respects not shown or described herein. Portions of the figures relating to the contact lens  111  which correspond to portions of the figures relating to the intraocular lens  11  are designated by corresponding reference numerals increased by 100. 
     Optically, the contact lens  111  has a central zone  118 , annular near zones  120  and  122 , annular far zones  124  and  126  and outer peripheral zone  127  which correspond, respectively, to the zones  18 - 27  of the intraocular lens  11 . In general, the magnitude of the vision correction powers, relative to the baseline diopter power, is reduced in the contact lens  111  relative to the magnitude of the vision correction powers in the optic  13  of IOL  11 . The contact lens  111  has a convex anterior surface  128  and a posterior surface  130  which is concave and configured to the desired shape of the eye of the wearer. Of course, the corrective powers could be provided on the posterior surface  130 , if desired. 
     Optically, the contact lens  111  is very similar to the optic  13  of intraocular lens  11 . The primary difference between the optic  13  and the contact lens  111  relates to the configuration of the inner near zone  120 . 
     Specifically, with reference to FIG. 8, inner near zone  120  includes a plateau  154  having an inner end  152  and an inner region  67  which has a substantially constant vision correction power. However, the region  69  of plateau  154  extending radially outwardly from inner region  68  includes vision correction powers which increase continuously and progressively to apex  71 . The vision correction power radially outwardly from apex  71  decreases continuously and progressively to point  158 . Thereafter, the vision correction power decreases continuously and progressively toward the baseline diopter power. 
     The vision correction power at point  158  is approximately 60% of the vision correction power at the apex  71 . In addition, the apex  72  is located away from inner end  152  about 70% of the total radial distance between point  152  and point  158 . The above-noted configuration of inner near zone  120  reduces the size of the halo caused by passing light to zone  120  relative to the halo caused by passing light to a similar inner near zone which has a substantially constant vision correction power across the entire distance from point  152  to point  158 . 
     FIG. 9 shows an alternate IOL  211  constructed in accordance with the teachings of the present invention. Except as expressly described herein, IOL  211  is similar to IOL  11 . Portions of IOL  211  which correspond to portions of IOL  11  are designated by the corresponding reference numerals increased by 200. 
     With reference to FIG. 9, the major difference between IOL  11  and IOL  211  relates to the configuration of outer far zone  226 . Specifically, outer far zone  226  begins at circular periphery  240  and decreases continuously and progressively to apex  88  which is located substantially equal radial distances from periphery  240  and circular periphery  242 . From apex  88 , the vision correction power increases continuously and progressively to the periphery  242 . 
     Outer far zone  226  is effective to enhance the performance characteristics of the lens when viewing a distant object in dim light or at night time. In addition, outer far zone  226 , or an outer far zone configured similarly to outer far zone  226  can be included in place of either outer far zone  26  in optic  13  of intraocular lens  11  or in place of an outer far zone of a contact lens, such as outer far zone  126  of contact lens  111 . 
     The present multifocal ophthalmic lenses provide substantial benefits, such as image quality when viewing a distant object in dim light or night time. The present lenses mitigate against the halos which are apparent or perceived as a result of causing light to pass to the outer near zone or zones of such lenses, relative to lenses including an outer near zone or zones which have substantially constant vision correction powers. Moreover, the present enhanced lenses can be cost effectively produced using conventional and well known techniques. Thus, the present lenses provide substantial benefits with few or no significant adverse effects. 
     While this invention has been described with respect to various specific examples and embodiments, it is to be understood that the invention is not limited thereto and that it can be variously practiced within the scope of the following claims.