Patent Publication Number: US-8526113-B2

Title: Liquid meniscus lens including gradient thickness dielectric coating

Description:
RELATED APPLICATIONS 
     This application claims priority to Provisional Patent Application U.S. Ser. No. 61/386,966 filed Sep. 27, 2010 entitled, “LIQUID MENISCUS LENS INCLUDING GRADIENT THICKNESS DIELECTRIC COATING”, and as a Continuation in Part Application to Non-Provisional U.S. patent application Ser. No. 13/095,786 which was filed on Apr. 27, 2011 and entitled “ARCUATE LIQUID MENISCUS LENS”, as well as Non-Provisional U.S. patent application Ser. No. 13/149,105 which was filed on May 31, 2011 and entitled “LENS WITH CONICAL FRUSTUM MENISCUS WALL”, as a Continuation in Part Application, the contents of each of which are relied upon and incorporated by reference. 
    
    
     FIELD OF USE 
     The present invention relates generally to a liquid meniscus lens, more specifically, it includes an arcuate liquid meniscus lens with a gradient thickness dielectric coating on portions of the meniscus wall. 
     BACKGROUND 
     Liquid meniscus lenses have been known in various industries. As discussed more fully below with reference to  FIGS. 1A and 1B , known liquid meniscus lenses were engineered in cylindrical shapes with a perimeter surface formed by points at a fixed distance from an axis which is a straight line. Known liquid meniscus lenses have been limited to designs with a first interior surface generally parallel to a second interior surface and each perpendicular to a cylindrical axis. Known examples of the use of liquid meniscus lenses include devices such as electronic cameras. 
     Traditionally, an ophthalmic device, such as a contact lens and an intraocular lens included a biocompatible device with a corrective, cosmetic or therapeutic quality. A contact lens, for example, can provide one or more of: vision correcting functionality; cosmetic enhancement; and therapeutic effects. Each function is provided by a physical characteristic of the lens. A design incorporating a refractive quality into a lens can provide a vision corrective function. A pigment incorporated into the lens can provide a cosmetic enhancement. An active agent incorporated into a lens can provide a therapeutic functionality. 
     More recently, electronic components have been incorporated into a contact lens. Some components can include semiconductor devices. However, physical constraints including the size, shape and control aspects of a liquid meniscus lens have precluded their use in an ophthalmic lens. Generally the cylindrical shape, sometimes referred to as the “hockey puck” shape of liquid meniscus lenses, has not been conducive to something that can work in a human eye environment. 
     In addition, a curved liquid meniscus lens includes physical challenges that are not necessarily present in a traditional design of a liquid meniscus lens with parallel sidewalls and/or optical windows. 
     SUMMARY 
     Accordingly, the present invention provides a liquid meniscus lens. Some preferred embodiments include an arcuate front curve lens and an arcuate back curve lens. The present invention provides for a meniscus wall with physical features conducive for one or both of attraction and repulsion of a liquid contained within the lens and forming a meniscus with another liquid. 
     According to the present invention, a first optic is proximate to a second optic with a cavity formed therebetween. Preferred embodiments include a first arcuate shaped optic proximate to a second arcuate shaped optic with a cavity formed therebetween. A saline solution and an oil are maintained within the cavity. Application of an electrostatic charge to a meniscus wall generally located in a perimeter area of one or both of the first optic and the second optic changes the physical shape of a meniscus formed between the saline solution and oil maintained within the cavity. 
     The present invention includes a liquid meniscus lens with gradient thickness dielectric coating on portions of the meniscus wall. In the current embodiment, the meniscus wall is formed into a shape essentially including a frustum of a cone. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  illustrates a prior art example of a cylindrical liquid meniscus lens in a first state. 
         FIG. 1B  illustrates the prior art example of a cylindrical liquid meniscus lens in a second state. 
         FIG. 2  illustrates a profile sliced cut away of an exemplary liquid meniscus lens according to some embodiments of the present invention. 
         FIG. 3  illustrates a cross section of a portion of an exemplary arcuate liquid meniscus lens, according to some embodiments of the present invention. 
         FIG. 4  illustrates additional exemplary aspects of an arcuate liquid meniscus lens. 
         FIG. 5  illustrates meniscus wall elements within an arcuate liquid meniscus lens, according to some embodiments of the present invention. 
         FIG. 6  illustrates a top down sectional view of a meniscus wall with gradient thickness dielectric coating, according to some embodiments of the present invention. 
         FIG. 7  illustrates a top down orthogonal view of a meniscus wall with gradient thickness dielectric coating showing position of a liquid meniscus, according to some embodiments of the present invention. 
         FIG. 8  illustrates a perspective view of a portion of an exemplary arcuate liquid meniscus lens wall showing a position of a liquid meniscus upon a meniscus wall with gradient thickness dielectric coating, according to some embodiments of the present invention. 
         FIG. 9  illustrates a cross section of a portion of an exemplary arcuate liquid meniscus lens, showing varying locations of the liquid meniscus on the meniscus wall, according to some embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention provides for a liquid meniscus lens with at least one of a front curve lens and a back curve lens defining a meniscus cavity of the liquid meniscus lens. Some preferred embodiments include one or both of the front curve lens and the back curve lens including an arcuate surface. Other embodiments include one or both of the front curve lens and the back curve lens being relatively planar, with a gradient thickness dielectric coating along the meniscus wall. 
     GLOSSARY 
     In this description and claims directed to the presented invention, various terms may be used for which the following definitions will apply: 
     Contact Angle: The angle at which the oil/saline solution interface, also referred to as the liquid meniscus boundary, meets the meniscus wall. In the case of a linear meniscus wall, the contact angle is measured as the angle between the meniscus wall and the line tangent to the liquid meniscus boundary at the point where the liquid meniscus boundary meets the meniscus wall. In the case of a curved meniscus wall, the contact angle is measured as the angle between the lines tangent to the meniscus wall and the liquid meniscus boundary at the point where they meet. 
     Lens: As used herein, a Lens means an article with a front surface and a back surface that is optically transmissive to a predefined range of wavelengths of radiation, such as, by way of example, visible light. A lens may include one or both of a front surface and a back surface which are essentially flat or one or both of a front surface and a back surface which are arcuate in shape. 
     Liquid Meniscus Boundary: The arcuate surface interface between the saline solution and the oil. Generally, the surface will form a lens that is concave on one side and convex on the other. 
     Meniscus Cavity: The space in an arcuate liquid meniscus lens between the front curve lens and the back curve lens in which oil and saline solution are maintained. 
     Meniscus Wall: A specific area on the interior of the front curve lens, such that it is within the meniscus cavity, along which the liquid meniscus boundary moves. 
     Optical Zone: as used herein refers to an area of an ophthalmic lens through which a wearer of the ophthalmic lens sees. 
     Sharp: A geometric feature of an internal surface of either a front curve or back curve lens piece sufficient to contain the location of a contact line of two predefined fluids on the optic. The sharp is usually an outside corner rather than an inside corner. From a fluid standpoint it is an angle greater than 180 degrees. 
     Referring now to  FIG. 1A , a cut away view of a prior art lens  100  is illustrated with an oil  101  and a saline solution  102  contained within cylinder  110 . The cylinder  110  includes two plates of optical material  106 . Each plate  106  includes an essentially flat interior surface  113 - 114 . The cylinder  110  includes an interior surface that is essentially rotationally symmetric. In some prior art embodiments, one or more surfaces may include a hydrophobic coating. Electrodes  105  are also included on or about the perimeter of the cylinder. An electrical insulator may also be used proximate to the electrodes  105 . 
     According to the prior art, each of the interior surfaces  113 - 114  is essentially flat or planar. An interface surface  112 A is defined between the saline solution  102 A and the oil  101 . As illustrated in  FIG. 1A , the shape of the interface  112 A is combined with the refractive index properties of the saline solution  102 A and the oil  101  to receive incident light  108  through a first interior surface  113  and provide divergent light  109  through a second interior surface  114 . The shape of the interface surface between the oil  101  and the saline solution  102  may be altered with the application of an electrical potential to the electrodes  105 . 
       FIG. 1A  illustrates a perspective view of the prior art lens illustrated at  100 . 
     Referring now to  FIG. 1B , the prior art lens  100  is illustrated in an energized state. The energized state is accomplished by applying voltage  114  across the electrodes  115 . The shape of the interface surface  112 B between the oil  101  and the saline solution  102 B is altered with the application of an electrical potential to the electrodes  115 . As illustrated in  FIG. 1B , incident light  108 B passing through the oil  101  and the saline solution  102 B is focused into a convergent light pattern  111 . 
     Referring now to  FIG. 2 , a cut away view of a liquid meniscus lens  200  with a front curve lens  201  and a back curve lens  202 . In various embodiments, the front curve lens  201  and the back curve lens  202  may include an arcuate lens or a substantially flat lens. In some preferred embodiments, the front curve lens  201  and the back curve lens  202  are positioned proximate to each other and form a cavity  210  therebetween. The front curve lens  201  includes a concave arcuate interior lens surface  203  and a convex arcuate exterior lens surface  204 . The concave arcuate interior lens surface  203  may have one or more coatings (not illustrated in  FIG. 2 ). Coatings may include, for example, one or more of electrically conductive materials or electrically insulating materials, hydrophobic materials or hydrophilic materials. One or both of the concave arcuate interior lens surface  203  and the coatings are in liquid and optical communication with an oil  208  contained within the cavity  210 . 
     The back curve lens  202  includes a convex arcuate interior lens surface  205  and a concave arcuate exterior lens surface  206 . The convex arcuate interior lens surface  205  may have one or more coatings (not illustrated in  FIG. 2 ). Coatings may include, for example, one or more of electrically conductive materials or electrically insulating materials, hydrophobic materials or hydrophilic materials. At least one of the convex arcuate interior lens surface  205  and the coatings are in liquid and optical communication with a saline solution  207  contained within the cavity  210 . The saline solution  207  includes one or more salts or other components which are ionically conductive and as such may be either attracted to or repulsed by an electric charge. 
     According to the present invention, an electrically conductive coating  209  is located along at least a portion of a periphery of one or both of the front curve lens  201  and the back curve lens  202 . The electrically conductive coating  209  may include gold or silver and is preferably biocompatible. Application of an electrical potential to the electrically conductive coating  209  creates either an attraction or a repulsion of the ionically conductive salts or other components in the saline solution  207 . 
     The front curve lens  201  has an optical power in relation to light passing through the concave arcuate interior lens surface  203  and a convex arcuate exterior lens surface  204 . The optical power may be 0 or may be a plus or minus power. In some preferred embodiments, the optical power is a power typically found in corrective contact lenses, such as, by way of non-limiting example, a power between −8.0 and +8.0 diopters. 
     The back curve lens  202  has an optical power in relation to light passing through the convex arcuate interior lens surface  205  and a concave arcuate exterior lens surface  206 . The optical power may be 0 or may be a plus or minus power. In some embodiments, the optical power is a power typically found in corrective contact lenses, such as, by way of non-limiting example, a power between −8.0 and +8.0 diopters. An optical axis  212  is formed through the back curve lens  202  and the front curve lens  201 . 
     Various embodiments may also include a change in optical power associated with a change in shape of a liquid meniscus  211  formed between the saline solution  207  and the oil  208 . In some embodiments, a change in optical power may be relatively small, such as, for example, a change of between 0 to 2.0 diopters of change. In other embodiments, a change in optical power associated with a change in shape of a liquid meniscus may be up to about 30 or more diopters of change. Generally, a higher change in optical power associated with a change in shape of a liquid meniscus  211  is associated with a relatively increased lens thickness  213 . 
     According to some embodiments of the present invention, such as those embodiments that may be included in an ophthalmic lens, such as a contact lens, a cross cut lens thickness  213  of an arcuate liquid meniscus lens  200  will be up to about 1,000 microns thick. An exemplary lens thickness  213  of a relatively thinner lens  200  may be up to about 200 microns thick. Preferred embodiments may include a liquid meniscus lens  200  with a lens thickness  213  of about 600 microns thick. Generally a cross cut thickness of front curve lens  201  may be between about 35 microns to about 200 microns and a cross cut thickness of a back curve lens  202  may also be between about 35 microns and 200 microns. Typically, a cross-sectional profile includes a defined variance in thickness at different locations in the lens  200 . 
     According to the present invention, an aggregate optical power is an aggregate of optical powers of the front curve lens  201  the back curve lens  202  and a liquid meniscus  211  formed between the oil  208  and the saline solution  207 . In some embodiments, an optical power of the lens  200  will also include a difference in refractive index as between one or more of the front curve lens  201 , the back curve lens  202 , the oil  208  and the saline solution  207 . 
     In those embodiments that include an arcuate liquid meniscus lens  200  incorporated into a contact lens, it is additionally desirous for the saline  207  and oil  208  to remain stable in their relative positions within the arcuate liquid meniscus lens  200  as a contact wearer moves. Generally, it is preferred to prevent the oil  208  from floating and moving relative to the saline  207  when the wearer moves. Accordingly, an oil  208  and saline solution  207  combination is preferably selected with a same or similar density. Additionally, an oil  208  and a saline solution  207  preferably have relatively low miscibility so that the saline solution  207  and oil  208  will not mix. 
     In some preferred embodiments, a volume of saline solution  207  contained within the cavity  210  is greater than the volume of oil  208  contained within the cavity  210 . Additionally, some preferred embodiments include the saline solution  207  in contact with essentially an entirety of an interior surface  205  of the back curve lens  202 . Some embodiments may include a volume of oil  208  that is about 66% or more by volume as compared to an amount of saline solution  207 . Some additional embodiments may include an arcuate liquid meniscus lens wherein a volume of oil  208  is about 90% or less by volume as compared to an amount of saline solution  207 . 
     Referring now to  FIG. 3 , a cutaway of an edge portion of an arcuate liquid meniscus lens  300  is illustrated. As discussed above, an arcuate liquid meniscus lens  300  includes combined front curve lens  301  and back curve lens  302  components. The front curve lens  301  and back curve lens  302  may be formed with one or more materials that are at least partially transparent. In some embodiments, one or both of the front curve lens  301  and the back curve lens  302  include generally optically clear plastic, such as for example, one or more of: PMMA, Zeonor and TPX. 
     One or both of the front curve lens  301  and the back curve lens  302  may be fashioned, for example via processes such as one or more of: single point diamond turning lathing; injection molding; digital mirror device free forming. 
     One or both of the front curve lens  301  and the back curve lens  302  may include a conductive coating  303 , as illustrated, the conductive coating  303  extending along a perimeter portion from  309  to  310 . In some preferred embodiments, a conductive coating  303  includes gold. The gold may be applied via a sputter process, vapor deposition or other known process. Alternative conductive coating  303  may include, by way of non-limiting example, aluminum, nickel, and indium tin oxide. Generally, the conductive coating  303  will be applied to perimeter areas of one or both of the front curve lens  301  and the back curve lens  302 . 
     In some embodiments of the present invention, a back curve lens  302  has a conductive coating  304  applied to specific areas. For example, portions about the perimeter of the back curve lens  302  may be coated from a first boundary  304 - 1  to a second boundary  304 - 2 . The gold coatings may be applied for example via a sputter process or a vapor deposition. In some embodiments, a mask may be used to apply the gold or other conductive material in a predetermined pattern around one or more perimeter portions of a front curve lens  301  or a back curve lens  302 . Alternative conductive materials may be applied using various methods and covering varying areas of the back curve lens  302 . 
     In some embodiments, a conductive pass through, such as, for example one or more holes or slots in a back curve lens  302  may be filled with a conductive filler material, such as, for example, a conductive epoxy. The conductive filler may provide electrical communication to a conductive coating on an interior surface of one or both of the front curve lens  301  and the back curve lens  302 . 
     In another aspect of the present invention, one or both of the front curve lens  301  and the back curve lens  302  may be created from multiple different materials wherein an optical zone generally in a central area of the front curve lens  301  and the back curve lens  302  (not illustrated) may include an optically transparent material and a peripheral zone may include an optically opaque area that includes an electrically conductive material. The optically opaque area may also include one or more of control circuitry and energy sources. 
     In still another aspect, in some embodiments, an insulator coating  305  is applied to a front curve lens  301 . By way of non-limiting example, the insulator coating  305  may be applied in an area from a first region  305 - 1  and extend to a second region  305 - 2 . Insulators may include, for example, Parylene C™, Teflon AF or other materials with various electrical and mechanical characteristics and electrical resistance. 
     In some specific embodiments, an insulator coating  305  creates a boundary area to maintain separation between the conductive coating  303  and a saline solution  306  contained in a cavity between the front curve lens  301  and the back curve lens  302 . Some embodiments accordingly include an insulator coating  305  patterned and positioned in one or more areas of one or both of the front curve lens  301  and the back curve lens  302  to prevent a positively charged conductor  303  and negatively charged saline solution  306  from coming into contact, wherein contact of a conductor  303  and a saline solution  306  will result in an electrical short circuit. Embodiments may include a positively charged saline solution  306  and a negatively charged conductor  303 . 
     Still other embodiments may allow for a short circuit between a conductor  303  and a saline solution  306  as a reset function of circuitry associated with the operation of the lens  300 . For example, a short circuit condition may equalize potential applied to the lens and cause the saline solution  306  and the oil  307  to revert to a default position. 
     Some preferred embodiments include a conductor  303  that extends from an area  309  on the interior of the cavity  311  to an area  310  external to the cavity  311 . Other embodiments may include a channel  312  through the front curve lens or the back curve lens which may be filled with a conductive material  313 , such as, for example, a waterproof conductive epoxy. The conductive material  313  may form or be connected to an electrical terminal external to the cavity. An electrical potential may be applied to the terminal and conducted to the coating via the conductive material  313  in the channel  312 . 
     The thickness of the insulator coating  305  may be varied as a parameter of lens performance. According to the present invention, charged components, including the saline solution  306  and the conductor  303 , are generally maintained on either side of the insulator coating  305 . The present invention provides for an indirect relationship between the thickness of the insulator coating  305  and an electrical field between the saline solution  306  and the conductor  303 , wherein the farther apart the saline solution  306  and the conductor  303  are maintained, the weaker the electrical field will be. 
     Generally, the present invention provides that electrical field strength may fall off dramatically as insulator coating  305  thickness increases. The closer together the fields are, the more energy that will generally be available to move a spherical liquid meniscus boundary  308 . As a distance between the saline solution  306  and conductor  303  increases, the farther apart electrostatic charges of the saline solution  306  and the conductor coating  303  will be and therefore the harder it is to get the spherical liquid meniscus boundary  308  to move. Inversely, the thinner the insulator coating  305 , the more susceptible is the lens to defects in an insulator coating  305 . Generally, even a relatively small hole in the insulator coating  305  will create an electrical short circuit and the lens will not function in an electrowetting fashion. 
     In some embodiments, it is desirable to include a saline solution  306  with density that is generally the same density of an oil  307  also contained within the lens  300 . For example, a saline solution  306  may preferably include a density that is within 10% of a density of an oil  307  and more preferably the saline solution  306  will include a density within 5% of a density of an oil and most preferably within about 1% or less. In some embodiments, a concentration of salts or other components within the saline solution  306  may be adjusted to adjust the density of the saline solution  306 . 
     According to the present invention, an arcuate liquid meniscus lens  300  will provide a more stable optical quality by limiting movement of the oil  307  in relation to the front curve lens  301  and the back curve lens  302 . One method of maintaining stability of movement of the oil  307  in relation to one or both of the arcuate front curve lens  301  and the back curve lens  302  is to maintain a relatively congruent density in the oil  307  and the saline solution  306 . In addition, due to the curve design of the interior surfaces of both the front curve lens  301  and the back curve lens  302 , the relative depth or thickness of a layer of saline solution  306  is diminished as compared to a traditional cylindrical lens design. In this scenario, the interfacial forces acting on fluids within the cavity may have a relatively greater contribution toward maintaining an unperturbed liquid meniscus boundary  308 . Consequently, the density matching requirement may become more relaxed in such cases. In some embodiments, the relative thinness of the fluid layers further supports the liquid lens boundary  308 . 
     In some preferred embodiments, the saline solution  306  provides a low refractive index as compared to the oil  307  which provides a relatively high refractive index. However, in some embodiments it is possible to include a saline solution  306  with a higher refractive index as compared to the oil  307  which in such cases provides a relatively lower refractive index. 
     An adhesive  314  may be used to secure the front curve lens  301  and back curve lens  302  in place proximate to each other, thereby retaining the oil  307  and saline solution  306  therebetween. The adhesive  314  acts as a seal so that there is no leakage of saline solution  306  or oil  307  from the curved liquid meniscus lens  300 . 
     Referring now to  FIG. 4 , a curved liquid meniscus lens  400  is illustrated with a liquid meniscus boundary  401  between the saline solution  406  and oil  407 . According to some preferred embodiments, a meniscus wall  405  is defined in the front curve lens  404  by a first angular break in an arcuate wall extending between  402  and  403 . The liquid meniscus boundary  401  will move up and down the meniscus wall  405  as electrical potential is applied and removed along one or more conductive coatings or conductive materials  408 . 
     In some preferred embodiments, a conductive coating  408  will extend from an area internal to the cavity  409  holding the saline solution  406  and the oil  407  to an area external to the cavity  409  containing the saline solution  406  and oil  407 . In such embodiments, the conductive coating  408  may be a conduit of an electrical potential applied to the conductive coating  408  at a point external to the cavity  409  to an area of the conductive coating  408  within the cavity  409  and in contact with the saline solution  406 . 
     Referring now to  FIG. 5 , a cut away view of an edge portion of an arcuate liquid meniscus lens  500  is shown with a front curve lens  501  and a back curve lens  502 . The arcuate liquid meniscus lens  500  may contain saline solution  503  and oil  504 . The geometry of the arcuate liquid meniscus lens  500  and the characteristics of the saline solution  503  and oil  504  facilitate formation of a liquid meniscus boundary  505  between the saline solution  503  and oil  504 . 
     Generally, a liquid meniscus lens may be viewed as a capacitor with one or more of: conductive coatings, insulator coatings, pathways, and materials present on or through the front curve lens  501  and back curve lens  502 . According to the present invention, a shape of a liquid meniscus boundary  505  and therefore a contact angle between the liquid meniscus boundary  505  and the front curve lens  501  change in response to an electrical potential applied to a surface of at least a portion of one or both of the front curve lens  501  and the back curve lens  502 . 
     According to the present invention, a change in an electrical potential applied to the saline solution  503  via the conductive coatings or materials changes a position of the liquid meniscus boundary  505  along a meniscus wall  506 . The movement takes place between a first sharp  506 - 1  and a second sharp  506 - 2 . 
     In preferred embodiments, the liquid meniscus boundary  505  will be at or near the first sharp  506 - 1  when a first magnitude of electrical potential is applied to the lens, such as, for example, a voltage and current correlating with an unpowered state or resting state. 
     Application of a second magnitude of electrical potential, sometimes referred to as a first powered state, may correlate with a movement of the liquid meniscus boundary  505  along the meniscus wall  506  generally in the direction of the second sharp  506 - 2 , causing the shape of the liquid meniscus boundary to change. 
     An applied voltage for transitioning between a first powered state and a second powered state may include, for example, a direct current voltage of between about 5 volts to about 60 volts. In other embodiments an alternating current voltage may also be utilized. 
     In some embodiments, the meniscus wall  506  will be a smooth surface in relation to the thickness of the insulator coating. A smooth meniscus wall  506  surface may minimize defects in the insulator coating. Additionally, because random irregularities in surface texture may result in uneven fluid motion and therefore cause uneven or unpredictable meniscus motion when energizing or de-energizing the lens, a smooth meniscus wall  506  is preferred. In some preferred embodiments, a smooth meniscus wall includes a peak to valley measurement along the meniscus wall  506  in the range of between about 1.25 nanometers to 5.00 nanometers. 
     In another aspect, in some embodiments, it is desirable for the meniscus wall  506  to be hydrophobic, in which case a defined texture, such as a nano-textured surface, may be incorporated in the design of the arcuate liquid meniscus lens. 
     In still another aspect, in some embodiments, the meniscus wall  506  may be angled relative to an optical axis of the lens. The angle can range from 0°, or parallel to the optical axis, to at or near 90°, or perpendicular to the optical axis. As illustrated, and in some preferred embodiments, the meniscus wall  506  angle is generally between about 30° and 50° in order for the arcuate liquid meniscus lens to function given the current contact angle between the liquid meniscus boundary  505  and the insulator-coated meniscus wall  506 . With the use of different materials or with different optical objectives, such as telescopic vision, the angle of the meniscus wall  506  may be closer to 0° or 90°. 
     According to the present invention, an angle of a meniscus wall  506  may be designed to accommodate a magnitude of movement along a meniscus wall  506  upon application of a specified electrical voltage. In some embodiments, as meniscus wall  506  angle increases, the ability to change lens power generally decreases within given lens size and voltage parameters. Additionally, if the meniscus wall  506  is at or near 0° relative to the optical axis, the liquid meniscus boundary  505  will be steered nearly straight onto the front optic. Meniscus wall angle is one of several parameters that can be tailored to provide various outcomes in lens performance. 
     In some preferred embodiments, the meniscus wall  506  is approximately 0.265 mm in length. However, the angle of the meniscus wall  506  together with the size of the overall lens will naturally affect meniscus wall  506  length in various designs. 
     It may generally be considered that an arcuate liquid meniscus lens  500  will fail if the oil  504  contacts the back curve lens  502 . Therefore, in preferred embodiments, the meniscus wall  506  is designed to allow a minimum clearance of 50 microns between the first sharp  506 - 1  and the back curve lens  502  at its nearest point. In other embodiments, the minimum clearance may be less than 50 microns, although the risk of lens failure increases as the clearance is reduced. In yet other embodiments, the clearance may be increased to mitigate the risk of lens failure, but the overall lens thickness will also increase which may be undesirable. 
     In still another aspect of some preferred embodiments of the present invention, the behavior of a liquid meniscus boundary  505  as it travels along a meniscus wall  506  may be extrapolated using Young&#39;s Equation. Although Young&#39;s Equation defines the balance of forces caused by a wet drop on a dry surface and assumes a perfectly flat surface, the fundamental properties can be applied to the electrowetted lens environment created within the arcuate liquid meniscus lens  500 . 
     A first magnitude of electrical energy may be applied to the lens, such as, for example, when the lens is in an unpowered state. During the application of the first magnitude of electrical energy, a balance of interfacial energies between the oil  504  and saline solution  503  is achieved. Such a state may be referred to herein as a liquid meniscus boundary  505 . The oil  504  and meniscus wall  506 , and the saline solution  503  and meniscus wall  506 , form an equilibrium contact angle between the liquid meniscus boundary  505  and the meniscus wall  506 . When a change in magnitude of voltage is applied to the arcuate liquid meniscus lens  500 , the balance of interfacial energies will change, resulting in a corresponding change in contact angle between the liquid meniscus boundary  505  and the meniscus wall  506 . 
     The contact angle of the liquid meniscus boundary  505  with the insulator-coated meniscus wall  506  is an important element in the design and function of the arcuate liquid meniscus lens  500  not only due to its role in the Young&#39;s Equation in movement of the liquid meniscus boundary  505 , but also because the contact angle is used in conjunction with other features of the arcuate liquid meniscus lens  500  to limit meniscus movement. 
     Discontinuities, such as sharps  506 - 1  and  506 - 2 , at both ends of the meniscus wall  506  act as boundaries for liquid meniscus  505  movement because it would require a significant change in applied electrical potential to effect a large enough change in liquid meniscus contact angle to move the liquid meniscus boundary  505  past one of the sharps. By way of non-limiting example, in some embodiments, a contact angle of the liquid meniscus boundary  505  with the meniscus wall  506  is in the range of 15° to 40° whereas the contact angle of the liquid meniscus boundary  505  with the step  507  beyond the second sharp  506 - 2  is perhaps in the range of 90° to 130° and in some preferred embodiments about 110°. 
     A voltage may be applied to the lens, resulting in movement of the liquid meniscus boundary  505  along the meniscus wall  506  toward the second sharp  506 - 2 . The natural contact angle of the liquid meniscus boundary  505  with the insulator-coated meniscus wall  506  will cause the liquid meniscus boundary  505  to stop at the second sharp  506 - 2  unless significantly more voltage is supplied. 
     At one end of the meniscus wall  506 , a first sharp  506 - 1  generally defines one limit beyond which the liquid meniscus boundary  505  will not typically move. In some embodiments, the first sharp  506 - 1  is constructed as a sharp edge. In other preferred embodiments, the first sharp  506 - 1  has a defined small radial surface which can be created with less possibility of defect. Conductive, insulator, and other possible desired coatings may not deposit evenly and predictably on a sharp edge, whereas a defined radius edge of the radial surface can be coated more reliably. 
     In some embodiments, the first sharp  506 - 1  is constructed at about a 90° angle with a defined radius of about 10 microns. The sharp may also be created with less than a 90° angle. In some embodiments, a sharp with a larger angle than 90° may be used to increase the sturdiness of the sharp, but the design would then take up more lens space. 
     In various embodiments, a defined radius of a sharp  506 - 1  and/or  506 - 2  may be in the range of 5 microns to 50 microns. A larger defined radius may be used to improve the reliability of the coatings, but at the cost of using more space within the tight confines of the lens design. In this, as in many other areas of lens design, tradeoffs exist between ease of construction, optimization of lens functions, and minimizing size. A functional, reliable arcuate liquid meniscus lens  500  may be made using a wide range of variables. 
     In some embodiments, a larger sharp radius may be used in conjunction with an improved surface finish on a side-wall between two adjacent sharps. In some embodiments, it may be desirable that a surface from a first radius (sharp) to a second radius (sharp) be smooth and without discontinuities wherein it is helpful to cut a mold used to fashion a sharp with the same tool. Radii included in a sharp may be cut into a mold tool surface, wherein the mold tool surface radius is larger than the sharp radius. Wherein the mold tool surface is a continuous surface including one or more sharps and a side wall. A larger tool radius may generally relate to a smoother surface finish of a corresponding cut. 
     A second sharp  506 - 2 , includes a feature designed to limit oil movement when voltage is applied to the arcuate liquid meniscus lens  500 . The second sharp  506 - 2  may also include, in some embodiments a generally pointed end, or in other embodiments, the second sharp  506 - 2  may include a defined radius of between 5 and 25 microns, most preferred 10 microns. A 10 micron radius performs well as a sharp and can be created using single point diamond turning lathe or injection molding processes. 
     A vertical or nearly vertical step  507 , extending to a start of the optical area  508  of the front curve lens  501  may be included on a side of the second sharp  506 - 2  opposing the meniscus wall  506 . In some embodiments, the step  507  is 120 microns in height, although it could be in the range of 50 to 200 microns. 
     In some embodiments, the step  507  may be angled at about 5° from optical axis. In other embodiments, the step  507  angle may be as little as 1° or 2° or may be angled more than 5°. A step  507  that is less angled from optical axis will generally act as a more effective limiter of meniscus movement because it would require a greater change in the contact angle of the liquid meniscus boundary  505  to move off of the meniscus wall  506  and onto the step  507 . The transition from the step  507  to the start of the optical area  508  is a 25 micron radius. A larger radius would unnecessarily consume more space within the lens design. A smaller radius is possible and may be implemented if necessary to gain space. The decision to use a defined radius rather than a theoretical sharp in this area as well as others in the lens is based, in part, on the potential move to an injection molding process for lens elements. A curve between the step  507  and the start of the optical area  508  will improve plastic flow during the injection molding process and result in a lens with optimal strength and stress-handling characteristics. 
     Referring now to  FIG. 6 , a top down sectional view shows a meniscus wall  601  with a dielectric coating  602 . The thickness of the dielectric coating  602  varies around the circumference of the meniscus wall  601 . In this exemplary figure, the dielectric coating  602  includes a first thickness along a y axis at points  603 , said first thickness being greater than a second thickness along a perpendicular x axis at points  604 . The thickness of the dielectric coating  602  forms a gradient between the thickest points  603  and thinnest points  604 .  FIG. 6  emphasizes the dielectric coating  602  and is not to scale. A conductive coating on the meniscus wall  601  under the dielectric coating  602  is not depicted in  FIG. 6 . 
     According to the present invention, cylinder power, axis and optical power features necessary to correct astigmatism may be produced in a liquid meniscus lens with gradient thickness dielectric coating  602  around the circumference of a meniscus wall  601 . When a magnitude of electrical potential is applied to the lens, a saline solution is more strongly attracted to the meniscus wall  601  in areas of thinner dielectric coating, such as points  604 , relative to areas of thicker dielectric coating, such as points  603  where attraction of saline solution to the meniscus wall  601  is weaker. In some preferred embodiments, saline solution strongly attracted to a meniscus wall  601  along one axis, such as an x axis in  FIG. 6 , and relatively weakly attracted to the meniscus wall  601  along a second perpendicular axis, such as a y axis in  FIG. 6 , will cause the liquid meniscus boundary to move and the oil within the meniscus cavity to assume a toric shape capable of correcting astigmatism. 
     The specific gradient thickness formed by a dielectric coating  602  and the axis at which it is created on a meniscus wall  601  within an arcuate liquid meniscus lens may be varied to achieve unique cylinder power and axis combinations for correction of astigmatism. The cylinder power for an astigmatic lens is influenced by the minimum and maximum thicknesses and the thickness gradient at which a dielectric coating  602  is created around the circumference of a meniscus wall  601 . The axis parameter required for astigmatism correction is controlled by the location of minimum and maximum points of dielectric coating  602  on a meniscus wall  601 , indicated in  FIG. 6  by points  604  and points  603  respectively. A liquid meniscus lens with gradient thickness dielectric coating may be designed with various methods of lens stabilization to maintain the correct orientation of the lens axis on the eye for astigmatic correction. Stabilization may be achieved using techniques such as ballasting or more advanced accelerated stabilization designs. The stabilization techniques may be implemented within the arcuate liquid meniscus lens or in a lens that encapsulates the arcuate liquid meniscus lens. 
     In the current embodiment, when a first magnitude of electrical potential is applied to the lens, the liquid meniscus boundary moves to a first state wherein a specific optical power for far vision may be achieved in combination with astigmatism correction. A second, relatively higher, magnitude of electrical potential may be applied to move the liquid meniscus boundary to a second state, resulting in correction for near vision together with astigmatism correction. 
     In other embodiments, power correction for far vision may be supplied by additional optical components within the lens assembly, such as by way of non-limiting example within a lens that encapsulates the arcuate liquid meniscus lens, while only near vision and astigmatism are corrected within the arcuate liquid meniscus lens. 
     Referring now to  FIG. 7 , a top down orthogonal view illustrates a meniscus wall  701  including a first sharp  702  and a second sharp  703 . The figure includes an optical zone  707  and a position of a liquid meniscus boundary  704 . In this exemplary figure, where a dielectric coating is thinnest, as was illustrated in  FIG. 6  along an x axis, attraction of a saline solution to the meniscus wall  701  is strongest, and the liquid meniscus boundary  704  has moved to points  706 , generally at or nearest the second sharp  703 . Where the dielectric coating is thickest, as was illustrated in  FIG. 6  along a y axis, attraction of a saline solution to the meniscus wall  701  is weakest, and the liquid meniscus boundary  704  is found at points  705 , generally closer to the first sharp  702 . The gradient in dielectric coating from thinnest areas to thickest areas causes a gradual transition in the position of the liquid meniscus boundary  704  upon the meniscus wall  701  from points  706 , generally nearer the second sharp  703 , to points  705 , generally nearer the first sharp  702 . 
     Referring now to  FIG. 8 , a perspective view of a portion of an arcuate liquid meniscus lens  800  is shown including a meniscus wall  801 , a first sharp  802 , a second sharp  803 , a step  805  and an optical zone  806 . A position of a liquid meniscus boundary on the meniscus wall  801  is indicated by line  804 . The perspective view of  FIG. 8  illustrates that the liquid meniscus boundary  804  is found generally at or nearest the second sharp  803  where the dielectric coating is thinnest at points  807   a  and  807   b , and the liquid meniscus boundary  804  is generally closer to the first sharp  802  where the dielectric coating is thickest at points  808   a  and  808   b , although  808   b  is not directly visible in the perspective view. The perspective view of  FIG. 8  shows the gradual slope of the liquid meniscus boundary  804  between one of its highest points on the meniscus wall  808   a , and its two lowest points on the meniscus wall  807   a  and  807   b . The opposite half of the liquid meniscus boundary  804 , although not entirely visible in  FIG. 8 , would be a mirror image of the portion visible between points  807   a  and  807   b.    
     Referring now to  FIG. 9 , a cut away view of an edge portion of an arcuate liquid meniscus lens  900  is shown with a front curve lens  901 , a back curve lens  902 , saline solution  903 , and oil  904 . A liquid meniscus boundary  905  is found between the saline solution  903  and oil  904 , contacting the front curve lens  901  on a meniscus wall  906 . When a first magnitude of electrical potential is applied, such as, for example, when the lens is in an unpowered state or a rest state, the liquid meniscus boundary  905  contacts the meniscus wall  906  at or near a first sharp  907 , whereas when a second magnitude of electrical potential is applied with a gradient thickness dielectric coating around the circumference of the meniscus wall, as described in  FIGS. 6 ,  7  and  8 , the liquid meniscus boundary  905  moves, resulting in contact points along the meniscus wall  906  at different positions based on the thickness of the dielectric coating. Where the dielectric coating is thickest and attraction of saline solution  903  to the meniscus wall  906  is weakest, the liquid meniscus boundary  905  will have generally more limited movement, such as to point  908  generally nearer the first sharp  907 . In areas of thinnest dielectric coating, greater attraction of the saline solution  903  to the conductor under the dielectric coating on the meniscus wall  906  will result in more movement of the liquid meniscus boundary  905 , such as to point  909  generally nearer a second sharp  910 . 
     Gradient thickness dielectric coating around the circumference of a meniscus wall may be formed by a number of techniques such as, by way of non-limiting example, applying the dielectric material using a shutter mask process to achieve a desired gradient thickness, applying an excess of dielectric material and using a diamond turning lathe process to remove dielectric material to form a desired gradient thickness, applying an excess of dielectric material and using a laser to ablate dielectric material to form a desired gradient thickness, and filling the front curve lens with dielectric material followed by insertion of an asymmetric overmold to form a desired gradient thickness. The gradient thickness within the dielectric coating is only necessary where the dielectric coating covers the meniscus wall. Other areas of the lens on which there may be dielectric coating do not require gradient thickness within the coating, although gradient thickness in these areas will not negatively affect the function of the arcuate liquid meniscus lens. 
     Another way to deposit a gradient thickness dielectric includes forming a thermal gradient on a desired surface, such that parylene condensation/deposition may be varied in a gradient manner. 
     In the present embodiment, the meniscus wall upon which the gradient thickness dielectric coating is found generally forms the shape of a conical frustum, a cross section of which shows the meniscus wall to be linear. Examples of a lens including a linear meniscus wall are described in the U.S. Patent Application Ser. No. 61/359,548, filed Jun. 29, 2010 and entitled “LENS WITH CONICAL FRUSTUM MENISCUS WALL”, which is incorporated herein by reference. In some embodiments, a gradient thickness dielectric coating may be included on meniscus walls of varying shapes and designs, such as by way of non-limiting example, a convex torus-segment meniscus wall, a concave torus-segment meniscus wall, a compound linear-convex meniscus wall, a multi-convex meniscus wall, a multi-concave meniscus wall, a multi-segmented linear meniscus wall, and a wall with microchannels. 
     While the invention has been described with reference to particular embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the scope of the invention. 
     Therefore, it is intended that the invention not be limited to the particular embodiments disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope and spirit of the appended claims.