Abstract:
A two optic accommodative lens system. The present invention also contemplates the use of a cam mechanism to adjust the distance power via adjustment of the dual lens separation when the eye is at distance vision stasis. The cam mechanism allows for distance/base power adjustment as needed.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     This invention relates generally to the field of intraocular lenses (IOL) and, more particularly, to accommodative IOLs.  
         [0002]     The human eye in its simplest terms functions to provide vision by transmitting light through a clear outer portion called the cornea, and focusing the image by way of a crystalline lens onto a retina. The quality of the focused image depends on many factors including the size and shape of the eye, and the transparency of the cornea and the lens.  
         [0003]     When age or disease causes the lens to become less transparent, vision deteriorates because of the diminished light which can be transmitted to the retina. This deficiency in the lens of the eye is medically known as a cataract. An accepted treatment for this condition is surgical removal of the lens and replacement of the lens function by an artificial intraocular lens (IOL).  
         [0004]     In the United States, the majority of cataractous lenses are removed by a surgical technique called phacoemulsification. During this procedure, an opening is made in the anterior capsule and a thin phacoemulsification cutting tip is inserted into the diseased lens and vibrated ultrasonically. The vibrating cutting tip liquifies or emulsifies the lens so that the lens may be aspirated out of the eye. The diseased lens, once removed, is replaced by an artificial lens.  
         [0005]     In the natural lens, bifocality of distance and near vision is provided by a mechanism known as accommodation. The natural lens, early in life, is soft and contained within the capsular bag. The bag is suspended from the ciliary muscle by the zonules. Relaxation of the ciliary muscle tightens the zonules, and stretches the capsular bag. As a result, the natural lens tends to flatten. Tightening of the ciliary muscle relaxes the tension on the zonules, allowing the capsular bag and the natural lens to assume a more rounded shape. In the way, the natural lens can be focus alternatively on near and far objects.  
         [0006]     As the lens ages, it becomes harder and is less able to change shape in reaction to the tightening of the ciliary muscle. This makes it harder for the lens to focus on near objects, a medical condition known as presbyopia. Presbyopia affects nearly all adults over the age of 45 or 50.  
         [0007]     Prior to the present invention, when a cataract or other disease required the removal of the natural lens and replacement with an artificial IOL, the IOL was a monofocal lens, requiring that the patient use a pair of spectacles or contact lenses for near vision. Advanced Medical Optics has been selling a bifocal IOL, the Array lens, for several years, but due to quality of issues, this lens has not been widely accepted.  
         [0008]     Several designs for accommodative IOLs are being studied. For example, several designs manufactured by C&amp;C Vision are currently undergoing clinical trials. See U.S. Pat. Nos. 6,197,059, 5,674,282, 5,496,366 and 5,476,514 (Cumming), the entire contents of which being incorporated herein by reference. The lens described in these patents is a single optic lens having flexible haptics that allows the optic to move forward and backward in reaction to movement of the ciliary muscle. A similar designs are described in U.S. Pat. No. 6,302,911 B1 (Hanna), U.S. Pat. Nos. 6,261,321 B1 and 6,241,777 B1 (both to Kellan), the entire contents of which being incorporated herein by reference. The amount of movement of the optic in these single-lens systems, however, may be insufficient to allow for a useful range of accommodation. In addition, as described in U.S. Pat. Nos. 6,197,059, 5,674,282, 5,496,366 and 5,476,514, the eye must be paralyzed for one to two weeks in order for capsular fibrosis to entrap the lens that thereby provide for a rigid association between the lens and the capsular bag. In addition, the commercial models of these lenses are made from a hydrogel or silicone material. Such materials are not inherently resistive to the formation of posterior capsule opacification (“PCO”). The only treatment for PCO is a capsulotomy using a Nd:YAG laser that vaporizes a portion of the posterior capsule. Such destruction of the posterior capsule may destroy the mechanism of accommodation of these lenses.  
         [0009]     There have been some attempts to make a two-optic accommodative lens system. For example, U.S. Pat. No. 5,275,623 (Sarfarazi), WIPO Publication No. 00/66037 (Glick, et al.) and WO 01/34067 A1 (Bandhauer, et al), the entire contents of which being incorporated herein by reference, all disclose a two-optic lens system with one optic having a positive power and the other optic having a negative power. The optics are connected by a hinge mechanism that reacts to movement of the ciliary muscle to move the optics closer together or further apart, thereby providing accommodation. In order to provide this “zoom lens” effect, movement of the ciliary muscle must be adequately transmitted to the lens system through the capsular bag, and none of these references disclose a mechanism for ensuring that there is a tight connection between the capsular bag and the lens system. In addition, none of these lenses designs have addressed the problem with PCO noted above.  
         [0010]     Prior art accommodative two lens systems using a movable “zoom” lens have inherently limited movement. The maximum sensitivity or movement magnification a (a unitless ratio) is defined as the axial movement of the lens per unit zonule movement and is derived by the following equation: 
 
 a=−B/A  
 
 where B is the projected distance of the zonule length which is in the order of 1.0 to 2.0 mm; and 
 
 A is the axial distance between the middle plane between the dual lens and the anterior surface of the anterior lens where the zonules terminate. 
 
         [0011]     Practically speaking, because of the lens thickness and dual lens separation requirement, A cannot be less than ˜1 mm. Therefore, α cannot be larger than 2, which defines the limit of the known dual lens accommodative approaches. This limit is too low for the dual optics design to achieve the objective of creating the greater than 2.25 diopters of accommodative amplitude that patients need for normal accommodation, which ideally results in a greater than or equal to 4.  
         [0012]     Secondly, existing dual optics accommodative implants do not manage any necessary change in the base power of the dual optics lens systems. Such changes can result from the inaccuracy of biometry, surgical variations, implant variations and inter-patient capsule variations. Consequently, patients can have refractive error after the implantation and need additional spectacles corrections that are not desired. In addition, potential post implantation capsule reaction and other ocular changes over time can result in the gradual development of refractive errors over time.  
         [0013]     Therefore, a need continues to exist for a safe and stable accommodative intraocular lens that provides accommodation over a broad and useful range and an adjustable base power.  
       BRIEF SUMMARY OF THE INVENTION  
       [0014]     The present invention improves upon the prior art by providing a two optic accommodative lens system. The present invention also contemplates the use of a cam mechanism to adjust the distance power via adjustment of the dual lens separation when the eye is at distance vision stasis. The cam mechanism allows for distance/base power adjustment as needed.  
         [0015]     Accordingly, one objective of the present invention is to provide a safe and biocompatible intraocular lens system.  
         [0016]     Another objective of the present invention is to provide a safe and biocompatible intraocular lens system that is easily implanted in the posterior chamber.  
         [0017]     Still another objective of the present invention is to provide a safe and biocompatible intraocular lens system that is stable in the posterior chamber.  
         [0018]     Still another objective of the present invention is to provide a safe and biocompatible accommodative lens system.  
         [0019]     Still another objective of the present invention is to provide a safe and biocompatible accommodative lens system having an adjustable base power.  
         [0020]     These and other advantages and objectives of the present invention will become apparent from the detailed description and claims that follow. 
     
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0021]      FIG. 1A  is an enlarged top plan view of the first lens of the lens system of the present invention.  
         [0022]      FIG. 1B  is an enlarged elevational view of the first lens of the lens system of the present invention.  
         [0023]      FIG. 2A  is an enlarged top plan view of the force transfer ring of the lens system of the present invention.  
         [0024]      FIG. 2B  is an enlarged partial cross-sectional view of the force transfer ring of the lens system of the present invention.  
         [0025]      FIG. 3A  is an enlarged top plan view of the capsule ring and second lens of the lens system of the present invention.  
         [0026]      FIG. 3B  is an enlarged partial cross-sectional view of the capsule ring and second lens of the lens system of the present invention.  
         [0027]      FIG. 4A  is an enlarged plan view of the lens system of the present invention shown in its low power, or distance vision state.  
         [0028]      FIG. 4B  is an enlarged partial cross-sectional view of the lens system of the present invention shown in its low power, or distance vision state.  
         [0029]      FIG. 5  is an enlarged partial cross-sectional view of the lens system of the present invention in its medium power, or intermediate vision position.  
         [0030]      FIG. 6  is an enlarged partial cross-sectional view of the lens system of the present invention in its high power, or near vision state. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0031]     As best seen in  FIGS. 1A-1B , first, or anterior lens  100  of the present invention generally includes first optic  110  and attached haptics  120 . Haptics  120  are attached to optic  110  by hinges  101 . Haptics  120  generally encircle optic  110  and contain widened tabs  180  having downward turn edges  104 . Tabs  180  are formed in a vaulted position, as best seen in  FIG. 1B  so that edge  104  lays in a plane separated from the plane in which optic  110  lays. As best seen in  FIGS. 2A-2B , force transfer ring  200  is generally circular having a central bore  140  into which anterior lens  100  fits. Ring  200  contains camming surface  201  that rests on tabs  180  on haptics  120  in the manner described below. Ring  200  further contains outer circumferential rim  203 . As best seen in  FIGS. 3A-3B , outer ring  300  is generally circular having a central bore  340  into which ring  200  fits. Ring  300  further contains internal circumferential ledge  301  on which rim  204  rests when ring  200  is fitted within ring  300 . Attached to ring  300  by haptics  420  is second or posterior lens  400 . Lenses  100  and  400  may be made from any suitable material such as a thermoplastic, a silicone, a hydrogel or a soft acrylic and contain any desired additives, such as ultraviolet or blue light blocking chromophores. Lenses  100  and  400  may further have any suitable design, such aspheric, toric, pseudoaccommodative or multifocal. Those skilled in the art will recognize that lenses  100  and  400  need not be implanted at the same time. For example, lens  400  and ring  300  may be implanted in an eye and the eye allowed to recover from the surgical trauma. After waiting such a healing period, bioptric and other physiological measurements may be made sufficient to calculate an accurate prescription for lens  100 , at which time lens  100  and ring  200  may be implanted.  
         [0032]     As best seen in  FIGS. 4-6 , lens assembly  500  is assembled within in an eye by first implanting outer ring  300  containing posterior lens  400  within the capsular bag. Anterior lens  100  is then placed within ring  300  in front of posterior lens  400  so that widened tabs  180  are caught under lower rim  302  of circumferential ledge  301  on ring  300 . Ring  200  is then placed within ring  300  so that camming surface  210  rests on tabs  180  of haptics  120  and circumferential rim  203  rests on circumferential ledge  301 . As show in  FIG. 4A-4B , lens assembly  500  is at its low power state—distance vision state. This state is achieved via the following sequence. When there is a need to dis-accommodate—to see distance objects, the ciliary muscle relaxes to cause enlargement of the ciliary ring diameter. The enlargement of the ciliary ring pulls the zonules outward in radial directions. Such outward zonule movement causes the anterior and posterior capsule portions to move towards each other. In other words, the capsular bag flattens. Flattening of the capsular bag causes ring  200  and edge  104  on haptic  120  of lens  100  to move toward each other because the anterior capsule portion (not shown) contacts ring  200  at anterior edge  202 , and because the posterior capsule portion (not shown) contacts lens  100  at edge  104  of haptic  120 . The movement stops when circumferential rim  203  rests on circumferential ledge  301  and when distal end  103  of tab  180  meets lower rim  302 . In this position, camming rim  201  presses against tabs  180  at area  102 . Consequently, hinge  101  is in a flexed, tensioned or sprung position. In this dis-accommodative position, the separation between anterior lens  100  and posterior lens  400  together with the respective powers of the two lenses determines the actual power of the lens assembly  500 .  
         [0033]      FIGS. 5-6 , show lens assembly  500  in accommodative positions. As one needs to accommodate—to see near objects, the ciliary muscle contracts causing ciliary ring diameter reduction. This reduction relaxes the holding force of the zonules, no longer flattening the capsule bag. With the capsular bag no longer holding haptics  120  and optic  110  flat, the tension in hinges  101  cause edges  104  to move away from optic  110 , thereby returning lens  110  into its natural vaulted state. Such vaulting moves lens  100  away from lens  400 , thereby causing an increase in lens separations resulting in an overall higher power of dual lens assembly  500 . The leverage ratio is determined by the ratio of the length of haptic  120  from hinge  101  to area  102 , and the length from area  102  to distal end  103 . By design adjustment, a higher ratio can be achieved such that the axial movement of optic  110  is much larger than that of ring  200 . Therefore, the amount of axial movement of optic  110  is not limited to the amount of axial movement of the anterior capsule, so that α&gt;2.25 can be achieved.  
         [0034]     In order to provide power adjustability to lens assembly  500 , as best seen in  FIG. 2B , camming surface  201  on ring  200  is not straight, but has an undulating profile, so that the distance between camming surface  201  and anterior edge  202  varies. Rotation of ring  200  causes variable axial movement of optic  110  because camming rim  201  presses against tabs  180  at area  102 , such pressure causing flexure of hinges  101 .  
         [0035]     This description is given for purposes of illustration and explanation. It will be apparent to those skilled in the relevant art that changes and modifications may be made to the invention described above without departing from its scope or spirit.