Abstract:
A multicomponent intraocular lens implantable in an optical system of a human eye, comprising: a base component and a front component, the front component comprising an attachment tab which extends from a circumferential side of the optical portion of the front component and engages the flange for attaching the front component to the base component, wherein the attachment tab of the front component comprises a resilient projection that protrudes away from the optical portion beyond the flange, wherein a portion of the resilient projection is located at a non-overlapping position with respect to the haptic of the base component in a circumferential direction around the optical portions, wherein the portion of the resilient projection has a back surface which is located backwards from a front surface of the haptic of the base component in the thickness direction of the base component.

Description:
CROSS-REFERENCE TO PRIORITY APPLICATIONS 
       [0001]    This application is a Bypass Continuation of International Patent Application No. PCT/EP2016/050081, filed Jan. 5, 2016, which claims priority to European Patent Application No. 15150142.6, filed Jan. 6, 2015. The disclosures of the priority applications are incorporated in their entirety herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates to the technical field of multicomponent intraocular lenses implantable in an optical system of a human eye for correction of visual disabilities. 
       BACKGROUND 
       [0003]    Cataract refers to a medical deficiency of the eye due to loss of transparency of the crystalline lens. An accepted treatment for this condition is surgical removal of the crystalline lens and replacement by an artificial intraocular lens. 
         [0004]    Multicomponent intraocular lenses (MC-IOL) for use in refractive cataract surgery are known in the art as illustrated e.g. by publications WO-A-2008094518, WO-A-2011006008 and WO-A-2012054854. A multicomponent intraocular lens includes a base component suitable for posterior chamber implantation and at least one front component that is detachably attached to the base component and that can be modified by either exchanging the front component or by altering the refractive properties in vivo at any post-operative time. The above-described structure permits the base component to form a platform upon which the at least one front component is placed and attached in a releasable manner. During routine cataract surgery, the MC-IOL replaces the crystalline lens of the human eye. Once a patient&#39;s eye has healed after such a surgery, the surgeon reenters the eye and modifies or replaces the front component, if necessary, to modify the optical characteristics of the eye until the desired levels for each optical characteristic are attained. 
         [0005]    MC-IOLs that are designed specifically to permit the easy exchange of front optical components at a post-operative period involve considerable benefits in terms of visual correction. This is because the actual surgery of implanting the lens in the first place, as well as variances in the manner in which the eye heals after implantation, potentially create distortions which may not stabilize for several months after the operation. Therefore, the ability to measure and to compensate for the distortions optimally takes place several months after surgery and cannot typically be predicted prior thereto. Since the same surgical wound may be used for both the primary and secondary operations, additional distortion due to wound healing would not be anticipated as a result of the second operation. Furthermore, the ability to exchange optical components of a multicomponent intraocular lens can be economical compared to removing, modifying, and re-implanting a single component lens, as well as easier to perform. 
         [0006]    The MC-IOL concept allows for adjustments or enhancement operations, beyond its use in primary cataract surgery to compensate for any miscalculation or any biological variability or any change in the condition of the eye over time after the primary operation. In order for these surgical adjustments to be workable, the surgeon must have easy access to the front component. To assure this, the front component must be left out of the capsule, in the sulcus. On the other hand, the base component is left in the capsule. 
         [0007]    In a prior art MC-IOL, the edges of the capsule are placed between the haptics of a front lens assembly and an underlying base lens. Vertically extending flanges of the base lens and their corresponding slots allow a space between the haptics of the front lens assembly and the base lens, so that a special instrument, referred to as a capsule snare, allows the surgeon to place the front lens assembly haptic above the edges of the capsule. The vertically extending flanges and corresponding slots position the front lens assembly in front of or away from the capsule, that is, in the sulcus, making surgical removal and replacement of the front lens assembly very safe and technically simple. Put another way, the flanges and slots assure easy removal and replacement of the front lens assembly during an enhancement operation, despite the normal healing process that involves capsule contracture around the base component. 
         [0008]    DE-U-202013009162 discloses an intraocular lens assembly comprising an intraocular lens structure for implantation in a capsular bag of an eye. The IOL comprises an optical structure having a periphery, at least two rear supports connected to the periphery and extend away therefrom, intended to be within the capsular bag when the IOL is implanted in the capsular bag, and at least two front legs connected to the periphery of the optical structure and extend away therefrom, intended to be located outside of the capsular bag. The front legs and the rear supports hold a front capsular bag between them. In an embodiment, the intraocular lens assembly further comprises a secondary intraocular lens for attachment to a front side of the IOL. The S-IOL comprises a secondary optical structure  35  and at least two fixing portions  37  each of which is intended to cooperate with one of the said front supports  8  to secure the S IOL to the IOL. In an embodiment, the capsular bag can be clamped between a front surface of the rear supports and a rear surface of the fixing portions  37 . 
         [0009]    The primary problem of this configuration is the difficulty or impossibility to rotate the lenses combination once they are assembled together because the tabs have captured the capsule edge and cannot be easily disengaged. Indeed, in case of a toric correction, orientation is determined and must be modified by the surgeon in the eye of the patient during surgery by rotating the elements inside the capsular bag when both lenses are assembled together. When assembled together, the system of DE-U-202013009162 will create a tension on the capsulorhexis which may prevent lens rotation, and thus, not allowing for proper axis orientation. In other words, it is not possible to manipulate such lens system inside the capsular bag to properly orient the lens axis. 
       SUMMARY 
       [0010]    A significant problem occurring with IOLs is the rotation away from its intended axis. This is mainly due to the shape of the IOLs, and especially the haptics, which are unable to prevent the IOL from rotating within the capsular bag. Indeed, the circular shape of most haptics is designed to fit to the dimensions of the capsular bag, which is also circular and thus, does not offer resistance. 
         [0011]    One objective of the present invention consists in providing an MC-IOL achieving improved stability when used in a posterior chamber implantation, in particular improved orientation stability of the MC-IOL. 
         [0012]    In an embodiment, the invention provides a multicomponent intraocular lens implantable in an optical system of a human eye, the multicomponent intraocular lens comprising: 
         [0000]    a base component having a front surface intended to be turned towards a front side of the human eye and a back surface opposed to the front surface in thickness direction of the base component and intended to be turned towards a back side of the human eye, the base component comprising a central portion and a haptic which extends from a circumferential side of the central portion away from the central portion, the base component further comprising a retaining member located at a periphery of the central portion and protruding on the front surface of the base component, and
 
a front component comprising an optical portion arranged in front of the front surface of the optical portion of the base component, the front component further comprising an attachment tab which extends from a circumferential side of the optical portion of the front component away from the optical portion and engages the retaining member for attaching the front component to the base component,
 
wherein the attachment tab of the front component comprises a resilient projection that protrudes away from the optical portion beyond the retaining member, wherein a portion of the resilient projection is located at a non-overlapping position with respect to the haptic of the base component in a circumferential direction around the optical portions, wherein the portion of the resilient projection has a back surface which is located backwards from a front surface of the haptic of the base component in the thickness direction of the base component.
 
         [0013]    Thanks to these features, it is possible to constrain the rim of the capsular bag between the haptic or haptics of the base component installed within the capsular bag and the adjacent resilient projection or projections of the front component arranged above the anterior surface of the capsular bag. Therefore, the multicomponent intraocular lens can be held firmly to the capsular bag. 
         [0014]    To that effect, the base component is firstly inserted through an opening or rhexis made in the anterior membrane of the capsular bag, a.k.a. front capsule. Then, a marginal portion of the front capsule is brought back onto the haptics. Next, during implantation of the front component, the resilient projection of the front component is engaged with the retaining member of the base component. Then, the distal end portion of the resilient projection is flexed frontwards from its natural position to be laid onto the marginal portion of the front capsule, so that the projection will resiliently urge the front capsule backwards. The combined effect of the base component haptic that backs the marginal portion of the front capsule from the inside at a first circumferential position and the resilient projection that urges the marginal portion backwards at a second, adjacent circumferential position is to create tensile stress in the front capsule around the opening. By reaction, by virtue of its positive tensile module, the front capsule resists the resilient force of the projection, so that a firm, non-sliding contact is created between the front capsule on the one hand, and the base component haptic and front component resilient projection on the other hand. 
         [0015]    Two basic functions of the lens assembly are fixation of the MC-IOL to the capsulorhexis and fixation of the components together. Besides, the attachment mechanism of the herein presented system allows to mount and attach the components together inside the capsular bag. At this stage, the one or more attachment tabs of the front component already engaged the retaining member of the base component and are below the anterior surface of the capsulorhexis. Then the attachment tabs of the front component are moved anteriorly in order to capture the capsulorhexis. So at this point, the attachment tabs of the front component remain above the capsulorhexis whereas the haptics of the base component are beneath the capsulorhexis. In order to properly orient the axis of the base component, the surgeon then elevates, simultaneously, the one or more attachment tabs of the front component freeing up the capsulorhexis and simultaneously rotate the MC-IOL in the proper orientation. Finally, the attachment tabs are released onto the anterior surface of the capsulorhexis, capturing the capsulorhexis and preventing any rotation. 
         [0016]    A number of different shapes can be employed for the retaining member of base component and attachment tab of front component which are intended to cooperate as an attachment device for attaching the front component to the base component. The or each attachment tab may have a cylindrical shape or other. 
         [0017]    In an embodiment, the or each retaining member comprises a flange having an elongated slot the length of which extends in the circumferential direction around the central portion, wherein the attachment tab of the front component has a flat shape and passes through the slot of the flange. With such geometry, it is possible to provide a reliable attachment between the front component and base component whereas the flat shape of the flange favors flexibility in a thickness direction thereof. 
         [0018]    In another embodiment, the attachment device includes a snap fastener, e.g. with a retaining member configured as a pin protruding on the front surface of the base component for engaging a corresponding recess in the attachment tab. 
         [0019]    In embodiments, the front component may be made of a single component or as an assembly of several subcomponents, e.g. an assembly of a mid-lens and a top lens attached together or an assembly comprising a stack of multiple lenses. Embodiments of such assemblies are disclosed in WO-A-2011006008. 
         [0020]    In an embodiment, the base component is implemented as a support component that serves as a fixed platform for carrying the front component is the eye. In that implementation, the central portion of the base component may be a hollow frame having a central aperture substantially aligned with the optical portion of the front component, for example as disclosed in FIG. 31 of WO-A-2012054854. 
         [0021]    In an embodiment, the central portion of the base component comprises an optical portion. 
         [0022]    In a preferred embodiment, the optical portion of the front component and/or the base component is substantially circular. The optical portion of the front component and/or the base component may also have different shapes, for example elliptical or other. 
         [0023]    In an embodiment, the optical portion of the front component comprises a back surface turned towards the front surface of the optical portion of the base component, wherein the back surface of the optical portion of the front component comprises a peripheral contact portion that is laid directly on the front surface of the optical portion of the base component all around the optical portions and a central, recessed portion that is spaced from the front surface of the optical portion of the base component, so as to define a chamber between said front surface and said back surface. 
         [0024]    In an embodiment, the front component comprises a through-hole that passes through a thickness of the optical portion to provide an access to the chamber from a front surface of the optical portion. 
         [0025]    In an embodiment, the or each attachment tab comprises a through-hole suitable for inserting a hook or catching tool. 
         [0026]    In an embodiment, the portion of the resilient projection is a distal end portion located at a distance from the optical portion of the front component. 
         [0027]    A number of different shapes can be employed for the haptic and the attachment tab in order to provide the configuration of a back surface of the portion, e.g. distal end portion, of the resilient projection that is located backwards from the front surface of the haptic of the base component. The amount of bending deformation that is necessary to bring the resilient projection from its rest position to its operating position over the front capsule depends on the position of the projection at rest. In an embodiment, the front surface of the distal end of the resilient projection and the front surface of the haptic lie in a same plane perpendicular to the thickness direction of the base component. Thus, the amount of deformation necessary is similar to the thickness of the resilient projection. In an embodiment, the back surface of the distal end of the resilient projection and the back surface of the haptic lie in a same plane perpendicular to the thickness direction of the base component. Thus, the amount of deformation necessary is similar to the thickness of the haptic. In embodiments, the haptic and the resilient projection may have the same thickness or different thicknesses. 
         [0028]    In an embodiment, the resilient projection at rest is angulated backwards in the thickness direction of the base component. In corresponding embodiments, the haptic of the base component at rest may be oriented transverse to the thickness direction of the base component, or angulated frontwards, or angulated backwards as well, e.g. with a lower angle than the resilient projection. 
         [0029]    In an embodiment, the or each haptic of the base component at rest is angulated frontwards in the thickness direction of the base component. In corresponding embodiments, the resilient projection of the front component at rest may be oriented transverse to the thickness direction of the base component, or angulated backwards, or angulated frontwards as well, e.g. with a lower angle than the haptic. 
         [0030]    A number of different shapes are suitable for the haptic or haptics of the base component. In particular, the base component may comprise at least one long haptic intended to engage an inner peripheral portion of a capsular bag of the human eye, in particular two long haptics extending in opposite directions to engage the capsular bag along a full diameter thereof. Alternatively or in addition, the base component may comprise at least one shorter haptic intended to remain at a distance from the inner peripheral portion of a capsular bag of the human eye. In embodiments, the longer and/or the shorter haptics may serve to tension the marginal portion of a front capsular membrane of the human eye in cooperation with the resilient attachment tab of the front component. 
         [0031]    In an embodiment, the base component comprises a loop-shaped haptic having two branches extending from the circumferential side of the central portion away from the central portion at two circumferential positions located on both sides of the resilient projection in the circumferential direction, wherein each of the two branches of the loop-shaped haptic has an end portion which extends farther from the optical or central portions than the distal end of the resilient projection and which is curved along the circumferential direction towards the resilient projection, so that the end portions of the two branches meet to form a closed loop around the resilient projection as seen in a projection along the thickness direction. With this configuration, the non-sliding contact between the front capsule and the multicomponent intraocular lens can be made stronger because the loop-shaped haptic backs the marginal portion of the front capsule from the inside all around the resilient projection that urges the marginal portion backwards. Thus, a contact surface of the haptic with the front capsule is enlarged. Preferably, the loop-shaped haptic is a long haptic. 
         [0032]    In an embodiment, the base component comprises a pair of haptics extending from the circumferential side of the optical portion away from the optical portion at two circumferential positions located on both sides of the resilient projection in the circumferential direction, wherein the resilient projection extends in a substantially radial position between the pair of haptics as seen in a projection along the thickness direction. With this configuration, the non-sliding contact between the front capsule and the multicomponent intraocular lens can be made stronger by alternating the haptics that back the marginal portion of the front capsule from the inside and the resilient projection that urges the marginal portion backwards. This configuration can be repeated in space around the multicomponent intraocular lens by providing a higher number of alternated haptics and resilient projections. This embodiment can be implemented with a pair of long or short haptics. 
         [0033]    In an embodiment, the base component comprises a pair of retaining members, e.g. flanges, which are diametrically opposed with respect to the central portion of the base component and wherein the front component comprises a pair of attachment tabs which are diametrically opposed with respect to the optical portion of the front component. 
         [0034]    In embodiments, the retaining members of the base component can be arranged at different positions, e.g. at aligned positions with the haptics of the base component in the circumferential direction or a offset positions from the haptics of the base component in the circumferential direction. Accordingly, the attachment tab of the front component may be at an adjacent or non-adjacent position with respect to the haptic of the base component in the circumferential direction. 
         [0035]    In an embodiment, the base component comprises an annular rib protruding on the front surface of the base component in the thickness direction of the base component and arranged around the optical portion of the front component, wherein an inner diameter of the annular rib substantially matches an outer diameter of the optical portion of the front component. In an embodiment, the flange and the annular rib of the base component are made as a single piece. Such an annular rib is useful for inhibiting cellular growth between the optical portions of the front and base components, e.g. capsular cell growth known as pearl formation. Alternatively or in combination, a number of other measures can be employed to reduce pearl formation. 
         [0036]    In an embodiment, the base component comprises an annular groove or annular rib formed on the front surface of the base component in the thickness direction of the base component and arranged around the central portion of the base component, wherein the front component comprises a corresponding annular rib or annular groove formed on the back surface of the front component. The annular rib is adapted to be engaged in the annular groove to attach the front component to the base component. 
         [0037]    Ensuring a strong contact between the front component and base component helps also reduce Elschnig&#39;s pearl formation. The strength of the contact depends on different parameters relating to the geometry and the materials of the base and front components. For example, the larger the contact portion of the front component that is laid directly on the front surface of the optical portion of the base component, the stronger the contact. For the selection of materials, different approaches may be employed. 
         [0038]    In an embodiment, the base component and the front component are both made of hydrophobic materials or the base component and the front component are both made of hydrophilic materials. In an embodiment, the base component and the front component are made of different materials, wherein a first component among the base component and the front component is made of a hydrophobic material and a second component among the base component and the front component is made of a hydrophilic material. By using materials having a similar or a different reaction to water, it is possible to adjust the interaction forces binding the two components. Hydrophobic materials may have a stronger effect for inhibiting cell growth. 
         [0039]    The short or long haptic or haptics of the base component, especially the loop-shaped haptic, and the attachment tab whose back surface ends backwards from the front surface of the haptic form a catching device for catching a rim portion of the front capsule. In embodiments, the multicomponent intraocular lens may be provided with a plurality of such catching devices. However, sufficient stability of the multicomponent intraocular lens may be obtained by catching a single portion of the front capsule. In a corresponding embodiment, the multicomponent intraocular lens is provided with a single catching device, so that manufacturing and implantation are made easier. 
         [0040]    In an embodiment, the front component comprises one single attachment tab whose back surface ends backwards from the front surface of at least one haptic of the base component, especially one single loop-shaped haptic of the base component, so as to catch one single portion of the front capsule. 
         [0041]    The multicomponent intraocular lens may be employed to correct a number of optical impairments of the eye, e.g. myopia, presbyopia, astigmatism, spherical aberrations, higher order aberrations and the like. The visual correction may be performed by both the base component and the front component, each of which comprises an optical portion that carries a portion of the total optical correction to be applied. In another embodiment, the optical portion of the base component is absent or optically neutral and the front component carries the whole optical correction to be applied. 
         [0042]    In an embodiment, the optical portion of the front component and/or base component is adapted to correct astigmatism, wherein the optical portion comprises an optical axis that characterizes the astigmatic correction, wherein the front component and/or base component further comprises an orientation mark to denote the optical axis of the optical portion, wherein the orientation mark is made of a material selected in the group of materials that absorb or reflect visible light and materials that are transparent to visible light and that absorb or reflect UV light, e.g. incorporated into the optical portion. In an embodiment, the orientation mark is a conformation of the front surface of the optical portion, e.g. a tiny groove or scratch. 
         [0043]    With materials that are transparent to visible light and that absorb or reflect UV light, it is possible to provide an orientation mark that will not impact the sight of the patient while being able to be seen by a surgeon under UV lighting during implantation of the intraocular lens or afterwards, e.g. in a secondary operation. This orientation mark is visualized as well as in the operating room and also in the office. 
         [0044]    In an embodiment, the front component and base component are foldable. In other embodiments, at least one of the optical portion of the front component and the central portion of the base component is stiff. In an embodiment, the whole base component is stiff. 
         [0045]    Aspects of the invention are based on the idea of slightly catching, clamping, pinching, winding or tightening a rim of the capsular membrane between an attachment tab of a front component and at least one haptic of the base component in order to improve rotational stability of the MC-IOL used in posterior chamber implantation. 
         [0046]    Aspects of the invention are based on the idea of ensuring exchangeability of the front component after healing. 
         [0047]    Aspects of the invention are based on the idea of inhibiting cell growth between the base component and the front component. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0048]    These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter, by way of example, with reference to the drawings. 
           [0049]      FIG. 1  is a perspective representation of a front lens of an MC-IOL in accordance with a first embodiment. 
           [0050]      FIG. 2  is a perspective representation of a base lens of the MC-IOL in accordance with the first embodiment. 
           [0051]      FIG. 3  is a partial perspective representation of the MC-IOL in accordance with the first embodiment, at rest. 
           [0052]      FIG. 4  is a partial perspective representation of the MC-IOL in accordance with the first embodiment in use, in a state of engagement with the front capsule of an eye. 
           [0053]      FIG. 5  is a sectional view of the MC-IOL in accordance with the first embodiment along a diameter of the optical portions. 
           [0054]      FIG. 6  is a partial perspective representation of a base lens in accordance with a second embodiment. 
           [0055]      FIG. 7  is a sectional view of the MC-IOL in accordance with a third embodiment along a diameter of the optical portions. 
           [0056]      FIG. 8  is a sectional view of the MC-IOL in accordance with a fourth embodiment along a diameter of the optical portions. 
           [0057]      FIG. 9  is a perspective representation of a base lens in accordance with a fifth embodiment. 
           [0058]      FIG. 10  is a perspective view of the MC-IOL in accordance with a fifth embodiment. 
           [0059]      FIG. 11  is a plane top view of the MC-IOL in accordance with a sixth embodiment in use, in a state of engagement with the front capsule of an eye. 
           [0060]      FIG. 12  is a perspective view of the MC-IOL in accordance with a seventh embodiment. 
           [0061]      FIG. 13  is a plane top view of the MC-IOL of  FIG. 12  in use, in a state of engagement with the front capsule of an eye. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0062]    With reference to  FIGS. 1 to 4 , an MC-IOL  1  in accordance with a first embodiment of the invention will now be described. The MC-IOL  1  consists of a front lens  10  shown on  FIG. 1  and a base lens  20  shown on  FIG. 2  and intended to receive the front lens  10 .  FIG. 3  shows the front lens  10  and base lens  20  in an assembled state of the MC-IOL  1  at rest.  FIG. 4  schematically illustrates the assembled MC-IOL  1  in use engaged with a capsular membrane  50  of the eye. 
         [0063]    The front lens  10  and the base lens  20  are thin, generally flat, foldable elements that can be manufactured from any suitable foldable materials, e.g. acrylic or silicone materials. Accordingly, the insertion of the front lens  10  and the base lens  20  into the eye requires an incision therein which is less than half as large as the larger diameter of the front lens  10  and base lens  20 . 
         [0064]    The front lens  10  includes a substantially circular optical portion that is made of a transparent material and resilient attachment tabs  12 , here in the number of two, which protrude radially around the optical portion  11 , i.e. perpendicularly to the thickness direction of the front lens  10 . The attachment tabs  12  shown here are arranged at two diametrically opposed positions. The attachment tabs  12  may be made of the same material as the optical portion  11  or of a different material, which is not necessarily transparent. As visible on  FIG. 3 , the attachment tabs  12  are angulated backwards along the thickness direction at rest, so as to pass behind the front surface  30  of the base lens  20  in the assembled state of MC-IOL  1 . 
         [0065]    The optical portion  11  has a central thickness ranging from 0.1 millimeters to 0.4 millimeters, and a diameter ranging from 1.50 to 8.50 millimeters, but preferably is between 5.50 and 7.00 millimeters. The optical portion  11  features an optical aperture ranging from 3.0 millimeters to 7.0 millimeters, with a preferable optical aperture of 5.5 millimeters. 
         [0066]    The base lens  20  includes a substantially circular optical portion  21  that may have similar, larger or smaller dimensions than the optical portion  11  and one or more haptics. In the embodiment shown, two long, loop-shaped haptics  22  are arranged at two diametrically opposed positions around the circular optical portion  21 . In the embodiment shown, a loop-shaped haptic  22  extends in a plane perpendicular to the thickness direction of the optical portion  21 . By convention, the thickness direction of circular optical portion  21  will be also referred to as vertical, whereas the plane perpendicular to the thickness direction of the optical portion  21  will be also referred to as horizontal. In service, the loop-shaped haptics  22  are intended to secure the base lens into the capsular bag of the eye by engaging an inner peripheral side of the capsular bag at two diametrically opposed positions. 
         [0067]    More precisely, a loop-shaped haptic  22  includes two protruding arms  23  that are spaced from one another along the periphery of the optical portion  21  and that extend substantially parallel away from the optical portion  21 , and a loop portion  24  connecting both protruding arms  23  at a distance from the periphery of the optical portion  21 . Each protruding arm  23  comprise a straight, proximal portion attached to the periphery of the optical portion  21  and a distal portion that curves away from the space  25  separating the proximal portions of the two protruding arms  23  at an angle of about 60° to 90°. The loop portion  24  extends as an arc of circle substantially parallel to the periphery of the optical portion  21  between the distal ends of the two protruding arms  23 . 
         [0068]    As visible on  FIG. 2 , each loop-shaped haptic  22  carries an attachment flange  26  for engaging an attachment tab  12  of the front lens  10 . More precisely, the attachment flange  26  comprises two vertical arms  27 . Each vertical arm  27  is arranged on the proximal portion of a protruding arm  23  on the edge of the optical portion  21 . An horizontal arm  28  bridges the gap between the two vertical arms  27  to define a substantially rectangular slot  29  in the attachment flange  26 . The horizontal arm  28  has a curved shape, e.g. as an arc of circle substantially parallel to the periphery of the optical portion  21 . 
         [0069]      FIG. 3  shows the MC-IOL  1  in the assembled state at rest, i.e. when no external forces are applied to it. The optical portions  11  and  21  are laid parallel against one another while each attachment tab  12  is inserted through the slot  29  of a corresponding attachment flange  26 . The attachment tab  12  has a shorter length than the distance between loop portion  24  and optical portion  21 , so that the protruding end of attachment tab  12  is entirely received in the space within the loop-shaped haptic  22 . Due to the backward angulation of attachment tab  12 , the protruding end of attachment tab  12  plunges through space  25  separating the proximal portions of the two protruding arms  23  so that an end portion of attachment tab  12  is located backwards from the front surface  30  of haptic  22 . 
         [0070]      FIG. 4  shows schematically the MC-IOL  1  in service when implanted in the posterior chamber of an eye. The anterior side of the capsular bag is partially shown at numeral  50 . It is recalled that the surgeon makes a substantially circular opening  51  called capsulo-rhexis in the front capsule  50  to remove the natural lens. This rhexis has a diameter somewhat bigger than the optical portions of the lenses and much smaller than the diameter of the capsular bag, to ensure that MC-IOL  1  is trapped within the bag. The base lens  20  is then inserted through the same opening  51 . Then, a marginal portion of the front capsule  50  is laid over the front surface of haptics  22 . Next, the front lens  10  is inserted and the attachment tabs  12  of the front lens  10  are engaged through the slots of the flanges  26  of the base lens  20 . At that time or subsequently, the attachment tabs  12  are flexed frontwards from their natural position to be laid onto the marginal portion of the front capsule  50 . In that state, the attachment tabs  12  resiliently urge the front capsule  50  backwards due to their intrinsic elasticity. Therefore, the front capsule  50  is held firmly between the front surface of each haptic  22  and the back surface of each attachment tab  12  in a manner similar to a sheet of paper clamped by a paper clip. 
         [0071]    An important outcome of the above procedure is that the MC-IOL  1  is held to the capsular bag and cannot freely rotate in the eye after implantation. Therefore, a steady and durable orientation is obtained, in particular around the vertical axis which corresponds to the central axis of the pupil. Such stability is especially important for achieving certain anisotropic optical corrections such as correction of astigmatism. 
         [0072]    The clamping of the front capsule  50  may be obtained at two diametrically opposed locations using both attachment tabs  12  and both haptics  22  in a symmetrical embodiment. 
         [0073]    This lens design requires a two-handed or two-instrument technique to rotate the lens at the time of the primary surgery to properly align the axis of astigmatism. As visible on  FIGS. 1 to 4  the front lens  10  may comprise one or more holes  17  around the optical portion  11  and one or more holes  18  in the attachment tabs  12  to facilitate manipulation of the front lens  10  during implantation. Tools (not shown) engaged in the holes  17  or  18  make it possible to grip the front lens  10  without damaging it. 
         [0074]    Alternatively, an asymmetrical embodiment makes it possible to clamp the front capsule  50  at a single location between one attachment tab  12  and one corresponding haptic  22 , whereas the other attachment tab  12  and the other haptic  22  do not have any clamping effect, e.g. are parallel. This alternative lens design only requires a one-handed or one-instrument technique to rotate the lens. 
         [0075]    In the above embodiment, each attachment tab  12  cooperates with a corresponding flange  26  to attach the front lens  10  to the base lens  20  in a releasable manner. In other words the two attachment tabs  12  and the two corresponding flanges  26  constitute two releasable attachment devices. In modified embodiments, similar attachment devices may be provided at a higher number of positions around the optical portions. In a modified embodiment, the whole MC-IOL comprises only one attachment device at only one position. 
         [0076]      FIG. 5  shows a cross-section of the MC-IOL  1  through the optical portions  11  and  21 . A chamber  31  is defined between the optical portions  11  and  21  due to the shape of the back surface  13  of optical portion  11 . Namely, back surface  13  includes a central recessed portion  14  surrounded by a flat annular portion  15  that abuts directly against the front surface  32  of base lens  20  in the attached state. As a result, four surfaces are available in this embodiment for shaping as a function of the desired optical corrections: front surface  16  and back surface  13  of front lens  10 , and front surface  32  and back surface  33  of base lens  20 . 
         [0077]    Hole  17  shown on  FIG. 5  communicates with chamber  31  so that fluid pressure can be injected through it to facilitate detachment of the front lens  10  from the base lens  20 , e.g. in a secondary operation. By contrast, the contact between annular portion  15  and front surface  32  holds the two lenses together through molecular phenomena, e.g. cohesion or adhesion depending on materials employed. 
         [0078]    A strong contact between the front lens  10  and the base lens  20  is desirable to prevent cellular growth between both lenses. Other means may be employed for that purpose as will now be explained with reference to  FIGS. 6 to 8 . 
         [0079]    In the embodiment of  FIG. 6 , elements that are identical or similar to those of  FIG. 2  are designated by the same numeral increased by 100. In base lens  120 , the optical portion is surrounded by an annular rib  35 . In use, the front lens optical portion (not shown) is inserted or snap-fitted within the annular rib  35 . The annular rib  35  is intended to fit closely the periphery of the front lens optical portion to also inhibit cell growth between both lenses. In the example shown, flange  126  is made continuous with the annular rib  35  and the horizontal arm of flange  126  is higher than the top of annular rib  35  in the thickness direction. 
         [0080]    In the embodiment of  FIG. 7 , elements that are identical or similar to those of  FIGS. 1-5  are designated by the same numeral increased by 200. Similar to base lens  120 , base lens  220  has an annular rib  35  surrounding the optical portion  221 . In that case, the horizontal arm  228  is aligned with the top of annular rib  35  in the thickness direction. 
         [0081]    Loop-shaped haptic  222  differs from loop-shaped haptic  22  in that it is angulated frontwards in the thickness direction. By contrast, in the example shown, attachment tab  212  extends horizontally from the optical portion  211  of the front lens  210  so that it ends within the inner space  225  of loop-shaped haptic  222 . Namely, at rest, a back surface  213  of attachment tab  212  is behind the front surface  230  of haptic  222 . In use, the MC-IOL  201  is locked to the capsular bag in the same manner as above, by flexing the attachment tab  212  frontward above the anterior membrane laid onto loop-shaped haptic  222 . 
         [0082]    In the embodiment of  FIG. 8 , elements that are identical or similar to those of  FIGS. 1-5  are designated by the same numeral increased by 300. Base lens  320  comprises an annular groove  37  surrounding the optical portion  321 . Front lens  310  comprises an annular rib  36  protruding backward from contact surface  315  and engaged in groove  37 . This arrangement also inhibits cell growth between both lenses. Alternatively, the groove may be arranged on the front lens and the corresponding rib may be arranged on the base lens. For the rest, the geometry is similar to  FIG. 7 . 
         [0083]    From  FIGS. 5 to 8 , it will be understood that different means of inhibiting cell growth and pearl formation between the lenses can be combined in diverse manners. 
         [0084]    Although the above-described base lenses have loop-shaped haptics, it will be understood that modified embodiments of the base lens may comprise haptics in different numbers and in different shapes. As an illustration,  FIG. 9  shows an embodiment in which elements that are identical or similar to those of  FIG. 2  are designated by the same numeral increased by 400. Base lens  420  includes optical portion  421  and four protruding haptics  422  that are spaced from one another along the periphery of the optical portion  421  and extend horizontally away from the optical portion  421 . Each haptic  422  includes a straight, proximal portion  423  attached to the periphery of the optical portion  421  and a distal portion  39  that curves away from the adjacent haptic  422  at an angle of about 60° to 90°. In the example shown, the proximal portions  423  of all four haptics  422  are substantially parallel. The base lens  420  can be employed with the front lens  10  in the same manner. 
         [0085]      FIG. 1  also illustrates the concept of an orientation mark  40  mechanically or chemically inserted or formed in the front lens  10  at the time of manufacturing to indicate an optical axis for astigmatic correction, so that the surgeon can orient properly the MC-IOL  1  within the eye. The orientation mark  40  is preferably made of a material or chemical dye visible by the surgeon under ultraviolet light, e.g. with the help of a UV lamp. Alternatively, orientation mark  40  is made as a local unevenness of the front surface that will be visible by the surgeon under oblique visible light, e.g. with the help of a slit lamp. In all cases, the orientation mark  40  is designed to remain substantially invisible from the patient. 
         [0086]    The attachments tabs  12  may not remain visible at all times by the surgeon during operations. The orientation mark  40  is preferably aligned with the attachments tabs  12  as an indication of their location. In an embodiment, a similar orientation mark may also appear on the base lens. 
         [0087]    In the embodiment of  FIG. 10 , elements that are identical or similar to those of  FIGS. 1-3  are designated by the same numeral increased by 500. The base lens  520  is shown in solid line whereas the front lens  510  is shown in phantom line. The two loop-shaped haptics  522  are connected to the top of the two flanges  526 , so that the loop-shaped haptics  522  are offset frontward with respect to the optical portion  521 . Thanks to this feature, the loop-shaped haptics  522  maintain the optical portion  521  further backwards into the eye, so that the MC-IOL  501  occupies less space in the eye sulcus, which facilitates the surgeon&#39;s intervention. This embodiment is also applicable to other haptic shapes. 
         [0088]      FIG. 10  shows the front lens  510  in service, i.e. with the attachment tabs  512  flexed frontwards to lie on the front capsule (not shown). At rest, the attachment tabs  512  may be parallel to the optical portion  511 , so that they lie entirely under the loop-shaped haptics  522 . 
         [0089]    In the embodiment of  FIG. 11 , elements that are identical or similar to those of  FIGS. 1-4  are designated by the same numeral increased by 600. Here, the base lens  620  has four shorter haptics  55  in addition of the two loop-shaped haptics  622 . The shorter haptics  55  are arranged horizontally around the central portion of the base lens  620  at different circumferential locations from the loop-shaped haptics  622 , i.e. e.g. at +45° and −45° of each loop-shaped haptic  622 . In addition, the flanges  626  are offset by 90° around the base lens compared to the embodiment of  FIG. 2 , so that each flange  626  is located at mid-distance between two shorter haptics  55 . 
         [0090]    The front lens  610  is configured in the same manner as in  FIG. 3 , except that it is also turned by 90° around the base lens in accordance with the modified position of the flanges  626 . Given that the attachment tabs  612  are angulated backwards at rest, they operate to catch the marginal portion of the front capsule  650  in the same manner as was described in  FIG. 4 , with the difference that the pair of adjacent shorter haptics  55  are now supporting the front capsule  650  against the resilient force of an attachment tab  612 . The loop-shaped haptics  622  which are located farther from the attachment tabs  612  play here a lesser role in the clamping of the front capsule  650 . 
         [0091]    In modified embodiments, the shorter haptics  55  may be angulated frontwards or backwards. The shorter haptics  55  may be provided in a different number and at different locations to exert a similar clamping function. 
         [0092]    Put differently, the loop-shaped haptics  622  and the shorter haptics  55  have different functions. Loop-shaped haptics  622  serve to engage a periphery of the capsular bag to hold the base lens  620  in the capsular bag, whereas shorter haptics  55  serve to engage a marginal portion of the front capsule around the rhexis  651  in cooperation with the attachment tabs  612 . By contrast, both functions may be combined in the haptics  22  of  FIG. 4 . 
         [0093]    Turning now to  FIGS. 12 and 13 , elements that are identical or similar to those of  FIGS. 1-4  are designated by the same numeral increased by 700. In the MC-IOL  701 , the base lens  720  has two shorter haptics  155  in addition of the two loop-shaped haptics  722 . The shorter haptics  155  are arranged horizontally around the central portion of the base lens  720  at different circumferential locations from the loop-shaped haptics  722 , i.e. at 90° of the loop-shaped haptics  722 . The loop-shaped haptics  722  of base lens  720  and the attachment tabs  712  of front lens  710  operate in the same manner as in  FIG. 4  to catch the marginal portion of the front capsule  750  of capsular bag  80 . In addition, front lens  710  comprises four further resilient projections  56  arranged around the central portion of the front lens  710  at different circumferential locations from the attachment tabs  712 , i.e. e.g. at +45° and −45° of each attachment tab  712 . The further resilient projections  56  are angulated backwards to exert a clamping of the front capsule  750  in cooperation with the shorter haptics of base lens  720 . Namely, a shorter haptic  155  backs the front capsule  750  from inside between two resilient projections  56  that are urged backwards by their intrinsic elasticity. Due to the combined effect of the loop-shaped haptics  722  and attachment tabs  712  on the one hand, and shorter haptics  155  and resilient projections  56  on the other hand, a rotational orientation of the MC-IOL  701  in the capsular bag is secured very stable manner. It must be noted that the size of the rhexis  751  is exaggerated on  FIG. 13  for the sake of clarity. 
         [0094]    The total frictional force between the MC-IOL and the front capsule depends on both the total contact surface of the above recited elements with the front capsule and the intensity of the resilient tensioning force exerted by the resilient projections and tabs. Therefore, for a given stability, a larger surface makes it possible to employ a lower force and conversely. The tensioning forces exerted on the capsular bag must be compatible with its natural resistance. MC-IOL  701  is especially suited for augmenting the contact surface. 
         [0095]    In modified embodiments, the shorter haptics  155  may be angulated frontwards or backwards. The shorter haptics  155  and resilient projections  56  may be provided in a different number and at different locations to exert a similar clamping function. 
         [0096]    The invention is not limited to the described embodiments. The appended claims are to be construed as embodying all modification and alternative constructions that may be occurred to one skilled in the art, which fairly fall within the basic teaching here, set forth. 
         [0097]    The use of the verb “to comprise” or “to include” and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. Furthermore, the  15  use of the article “a” or “an” preceding an element or step does not exclude the presence of a plurality of such elements or steps. 
         [0098]    In the claims, any reference signs placed between parentheses shall not be construed as limiting the scope of the claims.