Abstract:
A method and apparatus for forming a lens using two molds that interconnect together so that their respective interior surfaces form the negative image of the lens to be cast therein. The molds are preferably made of plastic. A monomer fills the volume formed by the interior surfaces of the molds and is cured or polymerized to form a lens having desired dimensions and characteristics. It is noted that this abstract is provided to comply with the rules requiring an abstract that will allow a searcher or other reader to ascertain quickly the subject matter of the technical disclosure. The abstract is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims pursuant to 37 C.F.R. § 1.72(b).

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention encompasses a method and apparatus for lens casting, in which two molds, preferably formed of plastic, are interconnected or coupled together to form a mold cavity having substantially the same dimensions of the lens to be formed therein.  
           [0003]    2. Background  
           [0004]    The art of casting lenses involves introducing a lens-forming material, such as monomer, into a volume and then polymerizing the lens-forming material into a solid object. The formed lens can be used for ophthalmic or specialty optics applications.  
           [0005]    Two mold pieces and a gasket typically form the volume that defines the dimensions of the lens to be cast. The prior art gaskets are known as “T-gaskets,” which include a bore having two ends that each complementarily receives a respective glass mold spaced apart a predetermined axial distance from the other mold. Different T-gaskets are required to form varying power lenses because they only allow one separation distance between molds. Accordingly, manufacturers must maintain separate T-gaskets for a +2 lens, another for a −3 lens, another for a −4 lens, etc.  
           [0006]    An improvement of this “T-gasket” design is disclosed U.S. Pat. No. 6,103,148, in which at least one of the two molds is slidably movable along the bore of the gasket. This design thus has a “universal” gasket that can be used to form different powers of lenses, whereas a given T-gasket may be used to form one power of lens and a different T-gasket is used to form another power.  
           [0007]    U.S. Pat. No. 5,551,663 teaches the use of plastic molds to function in a conventional gasket system. The disclosed molds are formed of plastic and are coated with a release-enhancing face that is not transferred to the formed lens; instead, the coating is designed to “protect the mold and also facilitate release of the lens or part after completion of the polymerization.” The purpose of this disclosed design, accordingly, is to allow the plastic molds to function exactly the same as conventional glass molds within a gasket system. However, the cost of the disclosed plastic molds is approximately equivalent to their glass counterparts, resulting in the lack of acceptance of this plastic design in the industry given their less sturdy construction.  
         SUMMARY OF THE INVENTION  
         [0008]    The present invention comprises a method and apparatus for casting a lens. A front mold and a rear mold, both of which are preferably formed of a plastic, interconnect to form a mold cavity that has substantially the same dimensions of the lens to be cast. That is, the front and rear together form a negative image of the lens to be formed.  
           [0009]    The front mold has a lens-forming surface and an edge circumscribing the lens-forming surface. The rear mold similarly has a lens-forming surface and a protrusion circumscribing its lens-forming surface. The protrusion of the rear mold is of a size to complementarily receive at least a portion of the edge of the front mold therein. When the front and rear molds are coupled together, they collectively form the mold cavity between their respective lens-forming surfaces.  
           [0010]    As one skilled in the art will appreciate, the design of this exemplary embodiment provides flexibility in casting lenses. As one consideration, the lens may be cast using two components—the front and rear molds—as opposed to three separate components—two molds and a gasket into which the molds are positioned.  
           [0011]    The molds of the present invention may be designed to cast lenses of different strengths. That is, for a lens with given optical surfaces, the center lens thickness can be altered simply by manufacturing rear molds having a protrusion of different heights and selecting the correct rear mold to form the correct power lens. The front and rear molds may also be rotatably movable relative to each other to form the correct optical surfaces, which is useful if the surfaces are asymmetric relative to each other.  
           [0012]    The plastic molds of the present invention also provide a labor and economic savings over use of a gasket with two molds. For example, with single-use life plastic molds, entire operations that lens-casting manufacturers now undertake using their glass counterparts and gaskets are eliminated, namely, cleaning and inspection. The start-up costs using the present invention are also lower than for an operation using glass molds and a gasket to cast lenses.  
           [0013]    Plastic molds also may be manufactured more reproducibly than their glass counterparts. As such, lenses cast using the present invention may be formed to more exacting specifications. 
       
    
    
     BRIEF DESCRIPTION OF THE FIGURES OF THE DRAWINGS  
       [0014]    [0014]FIG. 1 is a plan view of the front and rear molds of the present invention coupled together.  
         [0015]    [0015]FIG. 2A is a side cross-sectional view of FIG. 1, in which the mold cavity formed by the front and rear molds is of a dimension to cast a +2.00 D spectacle lens.  
         [0016]    [0016]FIG. 2B is a side cross-sectional view of FIG. 1, in which the mold cavity formed by the front and rear molds is of a dimension to cast a −2.00 D spectacle lens.  
         [0017]    [0017]FIG. 2C is a side cross-sectional view of FIG. 1, in which the mold cavity formed by the front and rear molds is of a dimension to cast a −6.00 D spectacle lens.  
         [0018]    [0018]FIG. 3A is a side cross-sectional view of the front mold shown in FIGS. 1 and 2A.  
         [0019]    [0019]FIG. 3B is a side cross-sectional view of the rear mold shown in FIGS. 1 and 2A.  
         [0020]    [0020]FIG. 4 is a top view of FIG. 1.  
         [0021]    [0021]FIG. 5 is a perspective view of the front and rear molds of FIG. 1 connected to a fill bag containing monomer. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0022]    The present invention is more particularly described in the following examples that are intended as illustrative only since numerous modifications and variations therein will be apparent to those skilled in the art. As used in the specification and in the claims, “a,” “an,” or “the” can mean one or more, depending upon the context in which it is used. The preferred embodiment is now described with reference to the figures, in which like numbers indicate like parts throughout the figures.  
         [0023]    The present invention comprises a molding or casting device  10  and an associated method that may be used to form all powers and geometric shapes of lenses, such as spectacle lenses. Referring generally to FIGS.  1 - 5 , the casting device  10  of the present invention includes a front mold  20  and a rear mold  40 , both of which are preferably formed of a plastic. The front mold  20  has a lens-forming surface  22 , an edge  28  circumscribing the lens-forming surface  22 , and a base  30 . The rear mold  40  likewise has a lens-forming surface  42  and a protrusion  46  circumscribing its lens-forming surface  42 .  
         [0024]    The protrusion  46  of the rear mold  40  is of a size to complementarily receive at least a portion of the edge  28  of the front mold  20  therein. It is desirable that when the protrusion  46  of the rear mold  40  interconnects with the edge  28  of the front mold  20 , a substantially liquid-tight seal exists therebetween.  
         [0025]    As shown in FIGS.  1 - 2 C, the front and rear molds  20 ,  40  collectively form a mold cavity  60  between their respective lens-forming surfaces  22 ,  42  when the molds  20 ,  40  are joined, coupled, or combined together. In the preferred embodiment, the formed mold cavity  60  has dimensions of a desired lens formable therein; stated differently, the mold cavity  60  is a replica image of the lens to be formed by the front and rear molds  20 ,  40 .  
         [0026]    A key dimension of the formed mold cavity  60  is its center thickness. In the illustrated embodiment, a desired center thickness may be structurally attained as a result of the design of the molds  20 ,  40  and, moreover, the center thickness may be changed by coupling molds having different physical attributes together. Specifically, referring now to the embodiment shown in FIG. 3A, the base  30  of the front mold  20  has a perimeter  32  and further defines a flange  34  extending around its perimeter  32 . The flange  34  preferably has a contacting surface  36  that is substantially planar. The lens-forming surface  22  of the front mold  20 , in conjunction, has an internal surface  24  having a nadir  26  or low point, in which the nadir  26  tangentially intersects a plane FM defined by the contacting surface  36  of the flange  34 . Accordingly, the nadir  26  of the lens-forming surface  22  and the contacting surface  36  of the flange  34  are at the same relative height when the front mold  20  is horizontally disposed.  
         [0027]    Now referring to FIG. 3B, the protrusion  46  of the rear mold  40  includes an end surface  48  that is substantially planar. The lens-forming surface  42  of the rear mold  40  has an apex  44  so that a plane RM tangential to the apex  44  is substantially parallel to and spaced apart from a plane FM′ defined by the end surface  48 . That is, when the rear mold  40  is horizontally disposed and supported by the end surface  48 , the apex  44  is spaced above the end surface  48  a predetermined distance-that distance corresponding to the desired center thickness of the lens to be formed within the mold cavity  60 .  
         [0028]    Accordingly, when the end surface  48  of the protrusion  46  abuts the contacting surface  36  of flange  34  (i.e., when the front and rear molds  20 ,  40  are joined together as shown in FIGS.  2 A- 2 C), the apex  44  and the nadir  26  of the respective lens-forming surfaces  22 ,  42  in the mold cavity  60  are spaced apart at the desired center thickness for the lens to be formed. Stated differently (but not explicitly shown in FIGS.  2 A- 2 C), when the molds  20 ,  40  are coupled together, the plane RM tangential to the apex  44  is spaced apart from the plane FM′ defined by the end surface  48 —which is co-planar with plane FM tangential to the nadir  26 —at a distance substantially equivalent to the desired center thickness of the mold cavity  60 . This design is one embodiment of a positioning means of the present invention.  
         [0029]    It is also contemplated that the center thickness may be varied for a selected front and rear mold  20 ,  40  by further including a spacer ring (not shown) between the end surface  48  of the protrusion  46  and the contacting surface  36  of flange  34 . The spacer ring has a fixed thickness, thereby increasing the center thickness of the mold cavity  60  by that thickness of the spacer ring. For example, a spacer ring having a thickness one millimeter in width disposed intermediate the end surface  48  and the contacting surface  36  would correspondingly result in the center thickness of the mold cavity  60 —and lens to be formed therein—increasing by one millimeter. Such spacer rings, accordingly, reduce the number of molds that need to be manufactured to provide an operator a full library of components to cast all desired dimensions and strength of lenses.  
         [0030]    In addition to center thickness, another relevant parameter in forming a desired lens is the geometric configuration or relationship of its two optical surfaces. When the two lens-forming surfaces  22 ,  42  are both spherical, the molds  20 ,  40  do not require any special rotational alignment relative to each other. This is because the respective surfaces have a constant radius along their different axes resulting in the surfaces being symmetric relative to each other.  
         [0031]    For other lenses, however, the present invention includes a means for orienting the front and rear molds  20 ,  40  at a predetermined rotational position with respect to each other. In the illustrated embodiment, the front and rear molds  20 ,  40  are rotatably movable relative to each other so that the two molds may be positioned at one of a plurality of selected relative rotational orientations. This orienting means thus allows the operator to alter the dimensions or shape of the mold cavity  60  to desired values when either or both of the lens-forming surfaces  22 ,  42  of the front and rear molds  20 ,  40  have asymmetric curvature. Examples of asymmetrical lenses that operators may typically cast include the front surface of a lens being spherical with an add power-or less frequently being a piano surface—and, in conjunction or independently, the back surface being cylindrical or toric. A discussion of the features and types of such asymmetrical surfaces may be found in U.S. Pat. No. 6,103,148, which is incorporated herein in its entirety by reference.  
         [0032]    Referring back to FIG. 1, the present invention also comprises an aligning means to allow the operator to appreciate the relative rotation of the two molds  20 ,  40  and position them accordingly. The aligning means shown in the illustrated embodiment comprises axis marks  50  on the rear mold  40  and an axis-positioning indicator  52  on the front mold  20 . The axis marks  50  extend from 0° and 180° and are positioned in registry with the asymmetrical lens-forming surface. If injection molding or similar technique forms the rear mold  40 , the markings are preferably etched into the die to ensure that an exact and permanent correspondence exists between the geometric characteristics of the lens-forming surface and the axis marks  50 . The position indicator  52  of the front mold  20  is also preferably integrally formed by injection molding the components as a single unit. One skilled in the art will also appreciate that aligning means may alternatively comprise the axis marks being located on the front mold and an axis-positioning indicator on the rear mold. Other methods of visually indicating the rotational position of the molds relative to each other may also be used.  
         [0033]    In preparing to cast the lens, the operator locates the position indicator  52  at a desired orientation relative to the axis marks  50  on the rear mold  40  either before the front and rear molds are joined together or afterwards (e.g., twisting the molds relative to each other once they are coupled together). The operator, thus, is able to position the two molds at a desired rotational location easily using the aligning means.  
         [0034]    When the operator joins the two molds  20 ,  40  together after selecting them, it is preferred that a connecting means exists so that the components do not inadvertently separate during the lens casting process. Such a connecting means can take numerous forms known in the art, including the protrusion  46  and edge  28  having a tight frictional fit, the components respectively having a complementary detent and projection (not shown) that “snap” together when the molds are at the desired positions relative to each other (e.g., the center thickness is correct).  
         [0035]    Other connecting means are also contemplated (not shown), including other designs in which the two molds  20 ,  40  snap into place or in which an external clip or containing device is used to hold the components at the correct axially-spaced position. The external connecting devices, such as a clip, are preferred when the spacer ring is used.  
         [0036]    In still another contemplated embodiment, the front and rear molds are formed as a single unit so they are integrally joined to each other. This may occur during the forming process (i.e., during injection molding) so that the operator receives a preformed molding structure in which the front and rear molds are stationarily positioned relative to each other. This unitary design, however, has less flexibility than interchanging front and rear molds.  
         [0037]    To form the lens once the front and rear molds  20 ,  40  are stationarily positioned together, a resin, such as a monomer or other lens-forming fluid, is added or injected into the mold cavity  60  and cured. To that end, the rear mold  40  defines a feed opening  70  through the protrusion  46 , which is shown in FIGS. 1 and 4. It is preferred that the rear mold  40  also defines a vent opening  72  through the protrusion  46 . The vent opening  72  provides fluid communication from the mold cavity  60  to outside of it (i.e., to ambient), which is shown in FIGS.  1 - 2 C and  4 . As best shown in FIGS. 1 and 4, when the front and rear molds  20 ,  40  are disposed upright, then the mold cavity  60  is substantially circular in plan view and the vent opening  72  is positioned at approximately the top center (the 12:00 o&#39;clock position) and the feed opening  70  is offset from there approximately sixty degrees (the 10:00 o&#39;clock position).  
         [0038]    Referring now to FIG. 5, a fill bag  80  or the like containing a fluid such as monomer may be interconnected to the feed opening  70 . More specifically, the fill bag  80  has an interior and an injection port  82  detachably connectable to the feed opening  70 . When the injection port  82  is linked to the feed opening  70 , the monomer located within the interior of the fill bag  80  may flow through the port into the mold cavity  60 .  
         [0039]    The injection port  82  and the feed opening  70  are preferably designed to complementarily engage each other. That is, the tip  84  of the injection port  82  is of a size to be complementarily received within the feed opening  70  to form a fluid-tight seal therebetween. More preferably, a means to detachably lock the tip  84  to the feed opening  70  is used so that separation between the two components is unlikely during transfer of monomer from the fill bag  80  into the mold cavity  60 . Examples of the locking means (not shown) include the tip  84  of the injection port  82  being self tapping, the tip  84  and the feed opening  70  each having complementarily threaded surfaces that mate with each other, or other interlocking designs. In addition, the locking means preferably prevents the tip  84  of the injection port  82  from extending completely through the feed opening  70  and contacting either of the lens-forming surfaces  22 ,  42  of the respective molds  20 ,  40 .  
         [0040]    One consideration that a person skilled in the art takes into account in casting lenses is the flow characteristics of the monomer traversing from the fill bag  80  into the mold cavity  60 . A primary concern is to avoid the introduction of air bubbles and ensure that any such bubbles escape out of the monomer before the curing begins; otherwise, the formed lens may be unacceptable if an air bubble discontinuity exists in the final product. In addressing this issue, the diameters of the tip  84  and feed opening  70  should be of a dimension and positioned to promote laminar flow when filling the mold cavity  60 . Additionally, as best shown in FIG. 1, the fill opening  70  is oriented to direct the monomer along the side of the mold cavity during the initial filling, instead of free falling completely to the bottom. As noted above, the vent opening  72  is also preferably located at the top of the mold cavity  60  (i.e., at the 12:00 o&#39;clock position) to vent air within the cavity  60  when displaced by the incoming monomer. The vent opening  72  being located at the top also allows any bubbles to escape before the curing process begins.  
         [0041]    Another consideration regarding injecting monomer involves positioning the mold cavity  60  so that the add power (not shown) is oriented to have its flat top portion substantially upright or vertical during filling the mold cavity  60 . This orientation assists in preventing air bubbles within the monomer from being trapped by this discontinuity in the lens-forming surface  22  of the front mold  20 . Bubbles are more likely to remain in the mold cavity  60  if, for example, the flat top is horizontally oriented.  
         [0042]    Referring again back to FIG. 5, the monomer bag  80  is at least partially constructed of a deformable surface on which the operator directs a compressive force so that one wall of the monomer bag  80  moves inwardly toward the opposed wall. When that compressive force is applied, the fluid monomer located within the interior is forced toward and out of the injection port  82  to enter the mold cavity  60  via the feed opening  70 . In constructing a system necessitating a minimal capital investment, the illustrated embodiment of the present invention is designed so that the operator may hand squeeze the monomer bag  80  to fill the mold cavity  60 .  
         [0043]    Other means of injecting monomer into the mold cavity  60  are contemplated. Examples of such systems using a deformable bag to fill the mold cavity  60 —particularly for more complex casting designs—is disclosed in U.S. patent application Ser. No. 10/095,130, filed on Mar. 11, 2002 and entitled “Method and Apparatus for Dispensing a Fluid,” which is incorporated herein by reference in its entirety. Monomer fill systems similar to the design disclosed in U.S. Pat. No. 6,103,148 is another option.  
         [0044]    Once monomer fills the mold cavity  60 , the monomer bag  80  is separated from the mold and then the monomer is cured (preferably with light as discussed in more detail below). As those skilled in the art appreciate, monomer shrinks approximately ten to fifteen percent by volume when it is cured. For some prior art designs in which the components forming the mold cavity  60  are stationarily positioned relative to each other (e.g., the T-gasket), this shrinkage creates internal stresses in the formed lens so that the cast lens sometimes requires annealing. The present invention is designed to reduce or eliminate such stresses by providing a reservoir volume in fluid communication with the mold cavity  60  to allow flow therebetween as the monomer volume shrinks.  
         [0045]    Specifically, referring to FIGS.  2 A- 2 C, the present invention preferably further comprises a fill channel  90  circumscribing the mold cavity  60  to act as the reservoir volume. The fill channel  90  is in fluid communication with both the vent opening  72  and the mold cavity  60 . As will be noted, the illustrated fill channel  90  has a larger cross-sectional area than the adjacent portion of the mold cavity  60  formed by the lens-forming surfaces  22 ,  42  of the two molds  20 ,  40 . When the monomer is being cured and correspondingly shrinks in volume, monomer from the fill channel  90  acts as a reservoir and is drawn into the mold cavity  60 . Because the fill channel  90  is in fluid communication with ambient via the vent opening  72 , this occurs without the stresses imparted in other systems that are sealed off from ambient.  
         [0046]    One skilled in the art will also appreciate that monomer that exists in the fill channel  90  and is cured to become part of the lens subsequently may be easily broken off. One skilled in the art may further appreciate that although not necessary, it may be desirable to block the light adjacent the fill channel  90  so that the monomer held therein remains in a liquid form longer during the curing process. The larger relative cross-sectional area (and thus greater volume) of the fill channel  90  also results in maintaining the monomer in liquid form longer than in the mold cavity  60  during the curing process to assist further in reducing stresses.  
         [0047]    As noted above, the molds  20 ,  40  of the present invention are preferably formed of a plastic material. Before discussing the advantages of using plastic molds and providing a few exemplary examples of suitable plastics that may be used with the present invention, it is important to note that one skilled in the art will appreciate that plastic is a broad term and very encompassing, namely, any of various synthetic or organic materials that can be molded or shaped, generally when heated, and then hardened into a desired form including, for example, polymers, resins, and cellulose derivatives.  
         [0048]    When selecting the specific type of material to form the molds  20 ,  40 , one skilled in the art will appreciate that to be useful in curing monomer, the selected plastic must transmit the curing radiation without melting, deforming, or stretching—at least until after the monomer is substantially cured or polymerized. Although thermal radiation is contemplated as a curing source and falls within the scope of the present invention, one skilled in the art will appreciate that the present invention may be better suited for photo curing. For photo curing of liquid resins, the desirable plastics include acrylic and methacrylic materials, an example of which is polymethylmethacrylate (PMMA). Some embodiments of available light transmissive PMMA are the OP1 and OP4 products by Cyro Industries, UV-T and V8- 25  by Rohm &amp; Haas, and CP75 from ICI. Other exemplary types of radiation transmissive plastics that may be used with the present invention include aliphatic polyesters, polyamides, polyurethanes, amorphous polyolefins, polycarbonates, polyimides and copolymers thereof. One skilled in the art will appreciate that these listed plastics are illustrative and the present invention is not limited to these examples.  
         [0049]    Another factor that one skilled in the art considers in selecting the plastics to use is that they do not adversely interface or react with the material to be cured. If, for example, it is desired to use PMMA to form the molds  20 ,  40  based on its cost or physical properties, then compatible monomers include long chain or high molecular weight monomers or prepolymers that do not attack the mold  20 ,  40 . Alternatively, the monomer desired to be used may be the primary consideration and the plastic forming the molds is chosen based on it being chemically resistant and non-reactive to that selected monomer.  
         [0050]    Using plastic to form the molds  20 ,  40  of the present invention provides potential benefits over casting systems currently used in the industry. One consideration is that the plastics may be injection molded. There is extensive use and experience in the industry of injection molding PMMA and acrylics using ceramic or metal molds. To that end, the front and rear molds  20 ,  40  of the present invention may be formed, for example, by fabricating metal dies into which PMMA is injection molded in an assembly process having a high throughput. Each of the molds  20 ,  40  of the present invention, accordingly, will be formed to the same high tolerances to which the die is formed. Glass molds, in contrast, cannot be fabricated to such exacting standards, so the present invention can cast an ophthalmic lens that is formed to more rigorous criteria. One skilled in the art will further appreciate that the front and rear molds  20 ,  40  may be formed using other suitable high throughput methods used in the art for fabricating plastics, in contrast to glass molds that cannot feasibly be mass-produced to the requisite tolerances.  
         [0051]    Another consideration with the front and rear molds  20 ,  40  is the economic comparison with conventional systems using two glass molds and a gasket. Although glass molds may be repeatedly used up to one hundred times or more, expenses accumulate that are associated with each casting, such as washing and drying that must ensure that the lens-forming surface is not contaminated. In fact, cleaning processes for glass molds are typically laborious, time-consuming and inefficient, involving manual scraping and soaking in noxious solvents. Furthermore, the glass molds must be inspected after each use and cleaning to insure suitability for another lens-making cycle. Plus, many times the glass molds are inadvertently chipped and/or broken before their potential useful life is reached. An associated problem is the occurrence of lens yield loss resulting from unwitting reuse of damaged lens molds, in which the operator sometimes does not discover that a glass mold is damaged until after a casting process has been completed.  
         [0052]    In comparison, when the plastic molds  20 ,  40  of the present invention are mass-produced, their cost is expected to be lower than for glass molds-which cannot feasibly be produced in bulk. Part of the reason is that plastics such as PMMA are relatively inexpensive. And, since PMMA and many other plastics are easy to cut or break after curing, removal of the polymerized lens from the molds once used is potentially quicker and easier than separating expensive glass molds, which must be delicately handled to attempt to ensure that their entire useful life is reached. Hence, the cost associated with using glass molds is believed to be more expensive over time than the use of plastic molds of the present invention, even single-use plastic molds.  
         [0053]    The economic considerations of the present invention also include the lower initial investment that a retailer must outlay before starting operations. That is, the initial start-up cost of using mass-produced plastic molds of the present invention is notably lower than for glass molds used in gasket systems because it is expensive to acquire and maintain the large inventory of glass molds needed for a lens molding operation. Likewise, in one embodiment of the present invention, assembly and fill machine(s) would be eliminated as hand assembly and filling are viable manufacturing methods. It is, accordingly, financially easier for new retailers to enter the market of casting ophthalmic lenses using the present invention.  
         [0054]    Another aspect of the present invention involves coating the lens-forming surfaces  22 ,  42  of the front and rear molds  20 ,  40  with an abrasion-resistant composition that is transferred to the lens when cured. More specifically, the lens-forming surfaces  22 ,  42  are preferably covered with a composition that transfers in situ to the optical surfaces of the cast lens as a protective coating on the final product. Without such a hardcoating on the lens that prevents or resists abrasion, scratching, and marring, the optical quality of the cast spectacles may more easily degrade from haze and poor image quality.  
         [0055]    One example of such an abrasion-resistant coating is disclosed in U.S. Pat. No. 5,049,321, which is incorporated herein by reference in its entirety. This patent discloses that the coating composition consists substantially of reactants having at least triacrylate functionality, a photoinitiator, and a polymerization inhibitor reactive with oxygen. After applying such a coating composition in the form of an ultraviolet curable liquid to the mold, the coating is subjected to ultraviolet radiation in an oxygen-containing environment such that the coating composition is cured to a hard/abrasion-resistant state. Then, when casting and curing the ophthalmic lens, the monomer is permitted to harden and react with acrylate groups at the coating/lens interface so that the coated lens is removed from the mold with the abrasion-resistant coating adhering thereto as an integral part of the surface of the optical surfaces of the lens. Other similar techniques of forming an abrasion-resistant coating on a cast lens are disclosed in U.S. Pat. Nos. 4,338,269 and 4,758,448, both of which are also incorporated herein by reference in their entireties.  
         [0056]    One skilled in the art will appreciate that although not necessary, using such an abrasion-resistant coating on the lens-forming surfaces  22 ,  42  produces a final product that consumers may prefer and that also allows the operator to separate more easily the front and rear molds  20 ,  40  from the lens cast therebetween. To that end, the abrasion-resistant coating may be applied to the lens-forming surfaces  22 ,  42  of the front and rear molds  20 ,  40  using a process the same as or similar to that disclosed in U.S. patent application Ser. No. 10/075,637, filed on Feb. 12, 2002 and entitled “Methods of Applying a Coating to an Optical Surface,” which is incorporated herein by reference in its entirety. Alternative treatment methods of the molds  20 ,  40  known in the art include spraying, dipping, brushing, flow coating, spin coating, and the like.  
         [0057]    The present invention also encompasses a method of casting a lens using the molds  20 ,  40  of the present invention. Of note, this process occurs without a gasket, which is typically employed in currently-used technologies. Stated differently, the present invention allows casting lenses with two components—the front and rear molds  20 ,  40  coupled together—instead of three components as required in other designs—two molds and a gasket.  
         [0058]    For an initial step, the method of the present invention involves providing front and rear molds  20 ,  40 . As indicated above, although it is contemplated that the components are prejoined, the front and rear molds  20 ,  40  are preferably combined or coupled together to form the mold cavity  60  by the operator. When the operator receives the prescription of a spectacle lens, he or she selects the front and rear molds  20 ,  40  that, together, form a mold cavity  60  having the dimensions of the lens desired to be formed. To that end, the front and rear molds  20 ,  40  are movable between a stored position and a molding position. In the stored position, the molds  20 ,  40  are separated from each other by, for example, being stored in designated areas or bins with molds having similar characteristics. In the molding position, the protrusion  46  of the rear mold  40  receives the edge  28  of the front mold  20  to form the mold cavity  60  after the operator retrieves the correct molds from the designated storage areas.  
         [0059]    It is contemplated using computer or other system (not shown) to assist the operator in selecting the correct molds  20 ,  40  when preparing to cast a lens. As one example, the present invention contemplates that the operator enters the parameters of the lens to be formed (e.g., the prescription including add power) into a computer or the like. Algorithms in an associated computer program determine the appropriate front and rear molds  20 ,  40  to be used to form the desired lens and then provide an output indicating this information. As one optional variation, this embodiment may additionally illuminate a light at the storage stations above the specific location where the appropriate molds  20 ,  40  are stored. The indicating lights assist the operator in locating the appropriate molds to reduce the chance of the operator inadvertently picking an incorrect mold to make the lens. Yet another option is to use a bar code or other tracking system (not shown) on the outer surfaces of the molds  20 ,  40  that the system scans to verify that the two proper molds are being used.  
         [0060]    After the operator locates the front and rear molds  20 ,  40  and is ready to reposition them from the stored to the molding position, the output of the optional computer system may further assist the operator by indicating additional positioning and aligning information. As discussed above, in the illustrated embodiment the front mold  20  is rotatably movable relative to the rear mold  40  so that the two molds  20 ,  40  are at one of a plurality of selected rotational orientations relative to each other. The computer may provide an output indicating the orientation of the two molds  20 ,  40  relative to each other when the lens-forming surfaces  22 ,  42  of the respective molds have asymmetric curvature. For the illustrated embodiment, the computer preferably indicates the appropriate location of the axis-positioning indicator  52  on the front mold  20  relative to the axis marks  50  on the rear mold  40 .  
         [0061]    As to the positioning of the molds  20 ,  40  to obtain the correct center thickness for the mold cavity  60 , this parameter is preferably considered in selecting the rear mold  40 , as different rear molds have protrusions of varying lengths in the illustrated embodiment that proportionally alter the center thickness of the mold cavity  60 . In an alternative embodiment discussed above, the computer may be programmed to indicate that a specific spacer ring be included between the front and rear molds  20 ,  40  to obtain the appropriate center thickness.  
         [0062]    However, one skilled in the art will appreciate that other means besides a computer system may be used to determine the correct mold to use with the present invention. As one skilled in the art will further appreciate, however, the present invention utilizing the computer system allows an operator with minimal training and understanding of the principles of lens casting to manufacture successfully lenses when a customer provides a prescription.  
         [0063]    After the front and rear molds  20 ,  40  are joined to form the mold cavity  60  of the desired dimensions and stationarily positioned relative to each other, the operator connects the monomer bag  80  to the feed opening  70 . The operator then injects the monomer into the mold cavity  60 , which may occur by hand squeezing the monomer bag  80  in the illustrated embodiment.  
         [0064]    During filling, the monomer enters via the feed opening  70  while the vent opening  72  allows displaced air to exit the mold cavity  60  to ambient. The filling method used with the present invention minimizes the quantity of monomer wasted and decreases the chances of air bubbles being formed within the lens. The monomer bag  80  may contain a quantity of monomer that is sufficient to form only a single lens or, alternatively, for multiple castings.  
         [0065]    Because monomer is a viscous fluid, it will inherently fill the mold cavity  60  at a controlled rate. By design, the fill rate may be further controlled by reducing the diameter of the feed opening  70  and tip  84  of the monomer bag  80 . Since the front and rear molds  20 ,  40  are formed of plastic, they can be clear or transparent so that the operator may visually observe the monomer entering and filling the mold cavity  60 . When the cavity  60  is filled with monomer (as well as the optional fill channel  90 ) so that the monomer reaches the vent opening  72 , the monomer bag  80  is removed from the front and rear molds  20 ,  40 . If necessary, the feed opening  70  is plugged, which may simply involve spot curing the monomer at that location to plug it or using a covering that snaps into the feed opening  70 . The vent opening  72 , however, preferably remains in communication with ambient during curing.  
         [0066]    The monomer within the mold cavity  60  is then cured to form the lens after ensuring that no bubbles are present. The preferred method involves curing using photo curing, although other curing methods are contemplated in conjunction with or alternatively to light. One primary advantage of photo curing, such as UV radiation, is that the plastic molds  20 ,  40  do not reach a temperature at which they may melt, deform, or stretch, which is more likely to occur with thermal radiation curing. UV curing methodologies are taught, for example, in U.S. Pat. Nos. 4,919,850; 5,524,419; 5,804,107; 5,981,618; 6,103,148; and 6,241,505, all of which are incorporated herein by reference in their entireties.  
         [0067]    After the monomer is cured to harden, then the operator removes the cured lens from within the mold cavity  60 . Because the preferred molds  20 ,  40  are formed of plastic, such as relatively inexpensive PMMA, it is contemplated in the presently preferred embodiment that the molds will have a one-use life. That is, the molds can be disposable so that there are no problems if the molds are chipped or broken during the removal of the lens from the mold cavity  60 . In fact, breaking the molds may assist in separating the cured lens from the mold cavity  60 , and the molds are more brittle than the cured lens so the lens does not also break. One skilled in the art will also appreciate that treating the lens-forming surfaces  22 ,  42  with abrasion-resistant coatings, such as the composition disclosed in U.S. Pat. No. 5,049,321, will assist in separating the lens from the mold as well as providing the lens with a protective scratch-resistant barrier. One skilled in the art will further appreciate that the plastic molds of the present invention can be used for more than one casting before their useful life ends.  
         [0068]    Although the present invention has been described with reference to specific details of certain embodiments thereof, it is not intended that such details should be regarded as limitations upon the scope of the invention except as and to the extent that they are included in the accompanying claims.