Contact lens

Abstract

A contact lens constructed to limit the water transmissibility of at least one area of the lens while maintaining at least a minimum oxygen transmissibility. The water transmissibility maximum and oxygen permeability minimum are achieved by a predetermined lens thickness of a single lens material or by the use of two or more material layers.

Claims

1. A soft contact lens consisting of: a single soft contact lens material having an oxygen permeability and a water permeability; wherein the soft contact lens has an average thickness of at least 0.2 millimeters, a water transmissibility below 13887.5 Barrers/cm, and an oxygen transmissibility above 24.1?10.sup.?9 (cm?ml O.sub.2)(sec?ml?mmHg); wherein the water permeability of the single soft contact lens material is less than 20,000 Barrers; and wherein the oxygen permeability of the single soft contact lens material is greater than 200 Barrers.

2. The soft contact lens of claim 1, wherein the single soft contact lens material is a polymer containing cross-linked polydimethylsiloxane.

3. The soft contact lens of claim 1, wherein the single soft contact lens material is a cross-linked polydimethylsiloxane.

4. The soft contact lens of claim 1, wherein the average thickness of the soft contact lens is at least 0.3 millimeters.

5. The soft contact lens of claim 1, wherein the average thickness of the soft contact lens is at least 0.29 millimeters.

6. A soft contact lens consisting of: a single soft contact lens material; wherein the soft contact lens has an average thickness of at least 0.2 millimeters, a water transmissibility that is below 13887.5 Barrers/cm, and an oxygen transmissibility above 24.1?10.sup.?9 (cm?ml O.sub.2)(sec?ml?mmHg).

7. The soft contact lens of claim 6, wherein the single soft contact lens material has a water permeability of less than 20,000 Barrers and an oxygen permeability of greater than 200 Barrers.

8. The soft contact lens of claim 6, wherein the single soft contact lens material is a cross-linked polydimethylsiloxane.

9. The soft contact lens of claim 6, wherein the average thickness of the soft contact lens is 0.29 millimeters.

10. The soft contact lens of claim 6, wherein the average thickness of the soft contact lens is at least 0.3 millimeters.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) The accompanying drawings, which are incorporated in and form a part of this specification, illustrate embodiments of the current disclosure and together with the description, serve to explain the principles of this invention. The figures are not intended to be exhaustive or to limit the invention to the precise form disclosed. It should be understood that the invention can be practiced with modification and alteration, and that the invention be limited only by the claims and the equivalents thereof.

(2) FIG. 1 is a cross-sectional view of a contact lens with a first thickness and a second greater thickness, in accordance with selected embodiments of the current disclosure.

(3) FIG. 2 is a cross-sectional view of a contact lens with two layers with varying permeabilities for oxygen and for water vapor in accordance with selected embodiments of the current disclosure.

(4) FIG. 3 is a cross-sectional view of a contact lens with multiple layers with varying permeabilities for oxygen and for water vapor in accordance with selected embodiments of the current disclosure.

(5) FIG. 4 is a cross-sectional view of a contact lens with an outer lens material and an inner material layer in accordance with selected embodiments of the current disclosure.

(6) FIG. 5 is a cross-sectional view of a contact lens with an outer lens material, an inner material layer and an adhesive layer between the layers in accordance with selected embodiments of the current disclosure.

(7) FIG. 6 is a cross-sectional view of a contact lens with an outer lens material and inner material layers displaced in regions of the contact lens in accordance with selected embodiments of the current disclosure.

(8) FIG. 7 is a chart of variation of composite permeability to oxygen and water as a fraction of those permeabilities originally expressed by a full thickness of only one of the materials prior to inclusion of a second material layer and the change to those original permeabilities by exchanging partial thicknesses of the original material layer by equivalent partial thickness layers of a second material, that second material having different permeabilities for oxygen and water vapor.

(9) FIG. 8 is a chart of a first scenario wherein the oxygen permeability ratios.sub.(PO1/PO2) are held constant.

(10) FIG. 9 is a chart of a second scenario wherein the oxygen permeability ratios.sub.(PO1/PO2) are held constant.

DETAILED DESCRIPTION OF THE INVENTION

(11) Many aspects of the current disclosure can be better understood with the references made to the drawings below. The components in the drawings are not necessarily drawn to scale. Instead, emphasis is placed upon clearly illustrating the components of the present disclosure. Moreover, like reference numerals designate corresponding parts through the several views in the drawings.

(12) A first embodiment of the present invention comprises a single lens material having an ultrahigh permeability to oxygen and water vapor. A thickness profile for the lens is selected to reduce the water transmissibility to at or below a maximum level while keeping the oxygen transmissibility to at or above a minimum level. Fornasiero and coworkers (2005) measured steady state diffusion of water through commercially successful hydrogel and silicone hydrogel lens materials while Rofojo (1980) measured water transport through silicone rubber lens materials. While the metrics for the two studies were reported to be different, a conversion is possible to put the water permeability into a common metric.

(13) In parallel, the lens thickness profiles of two of the commercially successful lenses are known. A resultant water transmissibility is calculated as the water permeability divided by the thickness. It is noteworthy that the water permeability varies with the humidity surrounding the material as it is measured. Further, the permeability may vary as the hydrogel materials dehydrate and become thinner. Even so, a mean value for a range of ambient humidity can be used for the purpose of the present disclosure.

(14) Water permeability can be reported as equal to pg/pm cm.sup.2 s?1 or equal to cm/pm and can be converted to cm.sup.3/pg H.sub.2O and mmHG/Atm which in turn can be converted to Barrers. Such a conversion allows the conventional hydrogel and silicone hydrogel measured values for water permeability to be compared to the reported values for water permeability of silicone rubber materials. The following table presents the values reported for comparison:

(15) TABLE-US-00001 TABLE 1 Water % Permeability Material Flux* Humidity Thickness** Barrers*** Polymacon 4.7 50 145 11110 Balafilcon 8.05 50 144 18964 Elastifilcon NA NA NA 40000 *10{circumflex over ()}.sup.6 .Math. g .Math. cm{circumflex over ()}.sup.2 .Math. s{circumflex over ()}.sup.1 **Steady State ***10.sup.?11 [cm.sup.3 .Math. cm]/[cm.sup.2 .Math. s .Math. mmHg]

(16) Historical reports of lens thickness for polymacon include commercialized lenses ranging from center thickness values from 0.04 to 0.18 mm. The majority of lenses have center thickness values between 0.08 and 0.12 mm or an average of 0.10 mm. Lenses made of polymacon have demonstrated sustained use for more than 50 years with no reports of lens adherence. The study of the long term commercial success of polymacon lenses and the absence of reports of lens adherence or sticking suggests that the water vapor transmissibility is sufficiently low to prevent depletion of the post lens tear layer. It is noteworthy that polymacon constitutes a small percentage of new fits because it also has a low oxygen permeability and falls below the Holden Mertz criteria for oxygen delivery for open eye wearing.

(17) The disclosure herein provides for the use of a pre-determined lens thickness as one embodiment for reducing the water transmissibility to an approximate level demonstrated by polymacon lenses while maintaining an oxygen transmissibility at or above the Holden Mertz criteria for open eye wearing. The Holden Mertz value set as the minimum oxygen transmissibility (Dk/t) for lenses of the present invention is 24.1?2.7?10.sup.?9 (cm.sup.3 O.sub.2)/(cm.sup.2.Math.s.Math.mmHg). By example, one variant of polydimethylsiloxane has a reported Dk=340?10.sup.?11 (cm.sup.2/sec) (mL O.sub.2)/(mL?mm Hg). It is possible for other variants of the same material to have higher or lower measured values of Dk.

(18) A lens made of a material with a Dk=340?10.sup.?11 (cm.sup.2/sec) (mL O.sub.2)/(mL?mm Hg) could have a center thickness as great as 0.141 cm to maintain a Dk/t=24.1?10.sup.?9 (cm?ml O.sub.2)/(sec?ml?mmHg). While this is an order of magnitude greater than commercialized lenses, the oxygen transmissibility would be expected to meet the open eye (daily wear) requirement. Such a thickness would also reduce the water transmissibility of the same lens to a level well below the level demonstrated by commercially successful polymacon and silicone hydrogel lenses.

(19) Since a lens thickness of 1.41 mm is excessive and unprecedented, the present invention is directed to minimizing the thickness to achieve a water transmissibility substantially equivalent to polymacon. A harmonic thickness value for polymacon lenses of 0.08 mm is selected to create the limiting maximum water transmissibility for the present invention. By way of example, the water transmissibility of polymacon at 50% humidity converted to permeability in Barrers is 11,110. Using the harmonic thickness of the lens as 0.008 cm, the water transmissibility (B/t) of the lens example is found to be 13,887.5. Continuing with the example, the reported permeability value of a variant of polydimethylsiloxane is found to be 40,000 Barrers. To achieve one embodiment of a lens of the present disclosure, the lens thickness (t) to achieve a B/t=13887.5 with a material with a water permeability in Barrers of 40,000 is calculated to be 0.029 cm, a thickness that is more than 3 times the average lens made of hydrogel and silicone hydrogel materials. In a particular embodiment, the contact lens has an average thickness of greater than 0.4 mm. In another embodiment, the contact lens has an average thickness of greater than 0.3 mm. In yet another embodiment, the contact lens has an average thickness of greater than 0.2 mm

(20) A particular embodiment of the current disclosure provides for a lens having the predetermined thickness of the lens area over the majority of the corneal surface regardless of the lens power. This differs from the predicate lenses made of polydimethylsiloxane which have only a high thickness at the geometric center of the lens and which rapidly thin due to the convex curvature of the front surfaces being shorter in radius than the concave curvature of the back surfaces of the lenses and for the purpose of producing high plus dioptric powers to correct aphakia. By way of example, a lens of the present invention having no power and with parallel surfaces or with the usual powers for refractive error correction comprises a thickness to produce a water transmissibility that is not greater than, B/t=13887.5 Barrers/cm; while producing an oxygen transmissibility, Dk/t, that is greater than or equal to 24.1?2.7?10.sup.?9 (cm?ml O.sub.2)/(sec?ml?mmHg).

(21) It should be recognized by those skilled in the art of contact lens design and manufacture that the most preferred solution to the dilemma of high water transport accompanying high oxygen permeability would be a material intrinsically possessing the permeabilities for these components such that the oxygen and water transport were both as required physiologically. Of course those skilled in the art should realize such a material would also have to meet all the requirements (biocompatibility, good wetting, appropriate mechanical properties, non-toxicity, durability and cost effectiveness) that are necessary for an acceptable contact lens. Work toward this goal continues to this day, however even after 50 years of searching, no such product has been reported.

(22) Given this fact, the embodiment proposed above offers one solution to the dilemma, while an alternative embodiment provides for a different approach: one which employs different materials each meeting some of the requirements for lens acceptability in a composite configuration wherein the individual limitations of the combined materials are mitigated by the extent and or location within the final product that the components are deployed. For instance, mechanical limitations can be mitigated by use of minimal thickness in the lens and biocompatibility or post lens tear film volume might be mitigated by sequestering such components within a sandwich of materials performing better in those aspects.

(23) More specifically an alternate embodiment of the present invention is a lens comprised of at least two separate layers deployed such that the more biocompatible layers would be the elements in contact with the anterior and posterior tear films. Elements possessing less desirable mechanical properties or oxygen permeabilities would be deployed in thin layers. The relative thickness of the individual layers within the sandwich would be imposed in relation to the oxygen permeability and water permeability of the individual materials. The determining factors for the relative thickness would be their summed permeabilities for oxygen and their summed permeabilities for water vapor, while attempting to keep the maximum oxygen permeability and the minimum water vapor permeability. It is important to note that it is not the arithmetic sum of the permeabilities; rather, their appropriately summed properties with recognition that the summed properties actually represent the resistance to permeation as opposed to the quantity of transmission allowed. The appropriate mathematical expression is:

(24) $\begin{array}{cc}\frac{E_t}{P}=\underset{i=1}{\overset{n}{.Math.}}\frac{E_i}{P_i}& \mathrm{Equation}1\end{array}$
Where P is the permeability to a specified permeant of the composite and E.sub.i the thickness of the i.sub.th layer, P.sub.i the permeability of the i.sup.th layer to the same permeant and E.sub.t the total thickness of the composite in mm. The permeabilities must be expressed in the same units preferably derived by similar methods. Thus a new permeability can be derived for the composite for each of the permeants of interest. Furthermore, it is convenient for each permeant to express its revised permeability as a fraction of its original permeability of the material having the highest permeation for that permeant. This expresses the compromise accepted for that permeant by sandwiching it with the other material layers.

(25) In a particular embodiment, it is desirable to maintain constant thicknesses of the sandwiched layers in the lens. In alternate embodiments, the thickness of the layers may be varied within the sandwich. By way of example, a contact lens of the present disclosure may require that oxygen delivery is more important to the cornea while oxygen deprivation might be less problematic beyond the corneal borders where some oxygen is supplied by the underlying vasculature. Conversely water loss from the tear pool beneath the lens is equally negatively impacted by water loss through the periphery of the lens as opposed to the center. The peripheral area for water loss is by nature larger than the central area of the lens. If the peripheral area possessed a thicker sandwiched layer resistant to water transport despite a concomitant loss of oxygen transport, the overall loss of the tear pool could be substantially impacted while the diminishment of oxygen availability would be mitigated by the lesser need for oxygen and availability of alternate sources under the periphery of the lens.

(26) It is also possible that fabrication of the sandwich requires adhesion of the individual layers and that adhesive films might be required between the primary layers. The permeabilities of these adhesive films are chosen such that in very thin films required for adhesion, they would have little impact on the overall permeability for the composite. However, if they present greater impact they too should be included in the composite permeability computation. In rare cases to get good adhesion there might be the necessity to insert a thin conforming layer between the primary layers such that the sandwich consists of primary layers and secondary layers with all such layers separated by adhesive films. Again the final composite permeability will be derived by the expression given above. In other cases there might be no need for adhesives, such as when the primary layers are intrinsically adhesive to each other or the internal layer(s), are simply encased within the outermost layers which extend slightly beyond the internal layers and are bonded there by adhesive at the perimeter, or are in fact extensions of a single encapsulating layer of the outermost layer formed during a molding process.

(27) The process of selecting the composition and thicknesses for the layers of the sandwich is most conveniently performed using derivatives of the mathematical expression given above. As an example, consider the oxygen and water penetration through a sandwich consisting of two outer layers of one material and one inner layer of another material. Further consider that the two materials had differing ratios of the permeability for oxygen and water such that while in one material the ratio water permeability highly favored the transmission of water over oxygen and in the second material the permeability for water was greatly reduced relative to that of oxygen. The objective is to create a composite sandwich of the two materials wherein the transmission of water is substantially reduced relative to the oxygen permeability and that the overall result is a reduced residual level of oxygen transport that remains within the level acceptable for the intended lens wearing schedule, while the water permeability of the composite is reduced from that of the 1.sup.st layer alone. Depending on the original magnitudes of the oxygen permeability, one can select a fraction of the original oxygen permeability as a target and compute the fraction of the water permeability remaining. These computations are exemplified below:

(28) $\begin{array}{cc}\frac{1}{\frac{\left(\frac{\mathrm{Tf}}{P_{O1}}\right)+\left(\frac{T\left(1-f\right)}{P_{O2}}\right)}{P_{O1}}}=\frac{P_{\mathrm{OC}}}{P_{O1}}& \mathrm{Equation}2\\ \frac{1}{\frac{\left(\frac{\mathrm{Tf}}{P_{W1}}\right)+\left(\frac{T\left(1-t\right)}{P_{W2}}\right)}{P_{W1}}}=\frac{P_{\mathrm{WC}}}{P_{W1}}& \mathrm{Equation}3\end{array}$
T is the total thickness of the composite; f is the fraction of the composite thickness occupied by the material having the highest oxygen permeability; P.sub.OC is the oxygen permeability of the composite; P.sub.O1 is the oxygen permeability of the first material; P.sub.O2 is the oxygen permeability of the second material; P.sub.wc is the water permeability of the composite; P.sub.W1 is the water vapor permeability of the first material; and P.sub.W2 is the water vapor permeability of the second material.

(29) Using literature values of permeabilities to water and oxygen for Polydimethylsiloxane and Amorphous Teflon at a thickness of 1 mm, .sub.PO1 is the oxygen permeability of the Polydimethylsiloxane; .sub.PO2 is the oxygen permeability of the Amorphous Teflon; .sub.PW1 is the water vapor permeability of Polydimethylsiloxane; and P.sub.W2 is the water vapor permeability of Amorphous Teflon. Given these values a composite can maintain greater than 80% of the oxygen permeability of pure PDMS while reducing the water permeation rate to little more than 10% of the permeability of pure PDMS.

(30) FIG. 7 is a chart of variation of composite permeability to oxygen and water. While the absolute values of the fractions as expressed in the chart at the end points are controlled by the absolute permeability values of the two components, another very important feature of these values is exposed in this chart. This feature is the asymmetry of the two functions. While the oxygen permeability regresses relatively linearly from its high point when none of the second component is present to its low point when only the second component is present, the water permeability function behaves quite differently. The water permeability of the composite compared to the water permeability of the first component drops precipitously at first inclusion of even very thin layers of the second component. Such asymmetry allows for superior enhancement of the water permeability with little impact on the oxygen permeability of the composite compared to the first material. A very thin layer of the second material suffices to vastly diminish the excessive water permeability of the first material leaving intact the first material's superior oxygen permeability.

(31) The aspects of the permeabilities employed in this composite that are most responsible for this preferred asymmetry in the result is the disparity in the ratios of the water permeability in the first material relative to that of the second (P.sub.w1/P.sub.w2) compared to the oxygen permeability in the first material relative to that of the second (P.sub.O1/P.sub.O2) The greater this disparity the greater the asymmetry. In this specific case where preserving oxygen permeability is desired and reducing water permeability is simultaneously preferred, selecting a second material keeping the oxygen permeability ratio (P.sub.O1/P.sub.O2) small while the water permeability ratio (P.sub.w1/P.sub.w2) is substantially greater leads to the successful relatively large reduction of water permeability with little reduction of the oxygen permeability by inclusion of a very thin layer of the second material within the first.

(32) FIG. 8 shows a chart of a first scenario wherein the oxygen permeability ratios (P.sub.O1/P.sub.O2) are held constant, but the ratio of water permeability ratios (P.sub.w1/P.sub.w2) is larger than that in FIG. 7. FIG. 9 shows a chart of a second scenario wherein the oxygen permeability ratios (P.sub.O1/P.sub.O2) are held constant, but the ratio of water permeability ratios (P.sub.w1/P.sub.w2) is less than that of FIG. 7. In these two charts, wherein the oxygen permeability ratios (P.sub.O1/P.sub.O2) are held constant, one sees that in two alternate cases, the water permeability ratios (P.sub.w1/P.sub.w2) differ (one less positive and one more positive). It is observed that the more positive this ratio the greater the preferred asymmetry in the functions.

(33) In a particular embodiment, the medium, or second component or material, within the first material, has a water permeability of less than 10,000 Barrers and an oxygen permeability of greater than 200 Barrers. Another embodiment provides for an area of the composite film measuring greater than fifty square millimeters of the contact lens that has a thickness of the medium providing a water transmissibility below a maximum value, such as 13887.5 Barrers/cm, while providing an oxygen transmissibility above a minimum value, such as 24.1?10.sup.?9 (cm?ml O.sub.2)/(sec?ml?mmHg).

(34) As discussed above, a permeant ratio for a particular permeant is calculated by taking the ratio of permeability for a permeant of a first material (e.g. P.sub.O1) to the (or over the) permeability for a permeant for a second material (e.g. P.sub.O2). In particular embodiments, the contact lens has different ratios of permeability for two permeants. As shown above, the composition of the two different layered materials can be chosen to make a second permeant ratio larger than the first permeant ratio. For example, the contact lens can have a first permeant ratio for the permeant oxygen that is smaller than a second permeant ratio for the permeant water (or water vapor). In a particular embodiment, the compositions of the layered materials are chosen such that first permeant ratio is 5 or smaller and the second permeant ratio is 10 or larger. In another embodiment, the first permeant ratio is 3 or smaller and the second permeant ratio is 20 or larger. In yet another embodiment, the first permeant ratio is 2 or smaller, and the second permeant ratio is 30 or larger.

(35) The differences between the permeability of a permeant of the composite contact lens and a layered material relative to that layered material can be expressed as a percent difference. In a particular embodiment, the composition of the medium and layer thicknesses of the medium may be chosen such that the permeability for a first permeant, such as oxygen, of the composite contact lens is no less than twenty percent of the permeability for the first permanent of the primary material, such as cross-linked polydimethylsiloxane. In another embodiment, the permeability for the first permeant of the composite film is no less than fifty percent of the permeability for the first permanent of the primary material. In yet another embodiment the permeability for the first permeant of the composite film is no less than seventy-five percent of the permeability for the first permanent of the primary material. In yet another embodiment the permeability for the first permeant of the composite film is no less than ninety percent of the permeability for the first permanent of the primary material. In yet another embodiment the permeability for the first permeant of the composite film is no less than ninety-five percent of the permeability for the first permanent of the primary material.

(36) Another embodiment has a permeability for the second permanent, such as water or water vapor, of the composite film which is no more than ninety-five percent of the permeability for the second permanent of the primary material, such as cross-linked polydimethylsiloxane. In another embodiment, the permeability for the second permeant of the composite film is no more than ninety percent of the permeability for the second permanent of the primary material. In an additional embodiment, the permeability for the second permeant of the composite film is no more than seventy-five percent of the permeability for the second permanent of the primary material. In yet another embodiment, the permeability for the second permeant of the composite film is no more than fifty percent of the permeability for the second permanent of the primary material. In a further embodiment, the permeability for the second permeant of the composite film is no more than twenty-five percent of the permeability for the second permanent of the primary material. In a further embodiment, the permeability for the second permeant of the composite film is no more than ten percent of the permeability for the second permanent of the primary material.

(37) Referring now to FIG. 1, it depicts a contact lens 100 in accordance with selected embodiments of the current disclosure. The contact lens 100 has a first thickness 101 approximating a conventional contact lens thickness bounded by a first anterior surface 102, and an additional lens thickness 103 of the same material for the purpose of reducing the water transmissibility of the finished lens to the limitations of the present disclosure. In a particular embodiment, the first lens thickness 101 is a primary material film, and the additional lens thickness 103 is the same primary material film where the primary material film is made at least in part from polymer containing cross-linked polydimethylsiloxane or an alternate material having a Dk equal to or greater than 200 Barrers.

(38) As will be understood by those of skill in the art, particular embodiments of the current disclosure may have an additional thickness 103 that is not limited to a location at the anterior surface, to a symmetrical configuration, to a uniform thickness profile, or to a centered position relative to the geometric center of the contact lens 100. For example, the additional thickness may be employed symmetrically or asymmetrically, or a regional placement may be employed. In this manner, the lens can be customized for the inclusion of a number and variety of thickness profiles to provide the desired oxygen and water transmissibilities of the finished contact lens 100. Furthermore, the first thickness 101 and the additional lens thickness 103 can be one contiguous element, or two distinct layers with encapsulated components each with a surface contacting the other.

(39) FIG. 2 depicts a contact lens 200 in accordance with selected embodiments of the current disclosure. The contact lens 200 has a first material film 201 bounded by a first material interface 202, and a second material film 203 bounded by an anterior surface 204, for the purpose of reducing the water transmissibility of the finished lens to the limitations of the present disclosure. In a particular embodiment, the first material film 201 is a primary material film, and the additional lens thickness 203 is a layered secondary material film, where at least one of the layered primary material film or layered secondary material film are made at least in part from polymer containing cross-linked polydimethylsiloxane or an alternate material having a Dk equal to or greater than 200 Barrers.

(40) As will be understood by those of skill in the art, particular embodiments of the current disclosure may have a secondary material film 203 that is not limited to a location at the anterior surface, to a symmetrical configuration, to a uniform thickness profile, or to a centered position relative to the geometric center of the contact lens 200. For example, the secondary material film may be employed posterior or anterior to the primary material film. The secondary material film may be employed symmetrically or asymmetrically, or a regional placement may be employed. In this manner, the lens can be customized for the inclusion of a number and variety of thickness profiles of the primary and secondary material films to provide the desired oxygen and water transmissibilities of the finished contact lens 200. Furthermore, the first thickness 201 and the additional lens thickness 203 can be one contiguous element, or two distinct layers with encapsulated components each with a surface contacting the other.

(41) FIG. 3 depicts a cross section of a segment of contact lens 300 in accordance with selected embodiments of the current disclosure. The multi-layered contact lens 300 has an anterior layer 301, a posterior layer 302, a first internal layer 303, a second internal layer 304 and a third internal layer 305. The contact lens 300 demonstrates relevant water transmissibility in the direction of the arrow 306, which is from the environment posterior to the posterior layer 302 and toward the environment anterior to the anterior layer 301.

(42) With continued reference to FIG. 3, the contact lens 300 demonstrates relevant oxygen transmissibility in the direction of the arrow 307, which is from the environment anterior to the anterior layer 301, and toward the environment posterior to the posterior layer 302. As will be understood by those of skill in the art, particular embodiments of the current disclosure may have layers that are not limited in number, to regional locations within or at the apparent relative depths in the lens 300, to a symmetrical configuration, to a uniform thickness profile, or to a centered position relative to the geometric center of the contact lens 300. For example, fewer or additional layers or a deeper or shallower placement of a layer may be employed, or a regional placement may be employed. In this manner, the lens can be customized for the inclusion of a number and variety of layers and the thickness of the layers can be determined to provide desired oxygen and water transmissibilities.

(43) FIG. 4 depicts a cross section of a layered contact lens 400 in accordance with selected embodiments of the current disclosure. The layered contact lens 400 has first material 401, and a second material layer 402. The second material layer 402 of the contact lens 400 has a variable thickness profile and is placed in a region of the contact lens 400. In a particular embodiment, the first material 401 is a layered primary material film, and the second material layer 402 is a layered secondary material film. The layered primary material film is made at least in part from polymer containing silicone acrylate. Alternatively, the layered primary material film is made at least in part from polymer containing cross-linked polydimethylsiloxane or an alternate material having a Dk of equal to or greater than 200 Barrers. The layered secondary material film is made from films having water permeability less than 10,000 Barrers, such as amorphous or crystalline fluorocarbon containing films. Alternatively, the layered secondary material film is made from polyurethane containing films having water permeability less than 10,000 Barrers. In yet another alternative embodiment, the layered secondary material film is made at least from silicone containing films having water permeability at least less than 10,000 Barrers.

(44) With continued reference to FIG. 4, the second material 402 is thicker at its center and thinner at its peripheral edges. The contact lens 400 includes a posterior layer of the first material 401 which is posterior to the second material layer 402 and which has a uniform thickness. Further, the contact lens 400 includes an anterior layer of the first material 401, which is anterior to the second material 402 and is thinner at its center and is thicker in the mid periphery of the anterior layer. As will be understood by those of skill in the art, particular embodiments of the current disclosure provide that the layers are not limited in number, to their locations at the apparent thicknesses within the contact lens 400, to a symmetrical configuration, to a uniform thickness profile, or to a centered position relative to the geometric center of the contact lens 400. For example, additional layers or a deeper or shallower placement of the layers may be employed, or a regional placement may be employed. In this manner, the lens can be customized for the inclusion of a number and variety of layers and the thickness of the layers can be determined to provide desired oxygen and water transmissibilities.

(45) FIG. 5 depicts a cross section of a layered contact lens 500 in accordance with selected embodiments of the current disclosure. The layered contact lens 500 has first material 501, a second material layer 502, and an adhesive layer 503. The second material layer contact lens 502 has a variable thickness profile and is placed in a region of the contact lens 500.

(46) With continued reference to FIG. 5, the second material 502 is thicker at its center and thinner at its peripheral edges. The contact lens 500 includes a posterior layer of the first material 501 which is posterior to the second material layer 502 and which has a uniform thickness. Further, the contact lens 500 includes an anterior layer of the first material 501, which is anterior to the second material 502 and is thinner at its center and is thicker in the mid periphery of the anterior layer. The adhesive layer 503 surrounds the second material layer 502. In an alternative embodiment, the adhesive layer 503 may not surround a second layer and may be applied to only one partial surface of region of a layer.

(47) As will be understood by those of skill in the art, particular embodiments of the current disclosure provide for one or more adhesives that may be applied having the same or different relative permeabilities and in a stacked manner or regionally. Furthermore, the layers may not limited in number, to their locations at the apparent thicknesses within the contact lens 500, to a symmetrical configuration, to a uniform thickness profile, or to a centered position relative to the geometric center of the contact lens 500. For example, additional layers or a deeper or shallower placement of the layers may be employed, or a regional placement may be employed. In this manner, the lens can be customized for the inclusion of a number and variety of layers and the thickness of the layers can be determined to provide desired oxygen and water transmissibilities.

(48) FIG. 6 depicts a cross section of a layered contact lens 600 in accordance with selected embodiments of the current disclosure. The layered contact lens 600 has first material 601, a second material layer 602 and a third material 603 peripheral to the second material 602. The second material 602 has a relatively uniform thickness profile and is placed in the central region of the contact lens 600. Layer 602 may alternatively have the same composition as layer 601. The third material 603 has a variable thickness and is placed in the mid-peripheral region of contact lens 600.

(49) With continued reference to FIG. 6, the second material 602 is relatively uniform in its thickness. The third material 603 is thicker at its center and thinner at its peripheral edges. The contact lens 600 includes a posterior layer of the first material 601, which has a relatively uniform thickness and which is posterior to the second material layer 602 and the third material 603. Further, the contact lens 600 includes an anterior layer of the first material 601, which is thinner at its center, thicker in the mid periphery of the anterior layer, and anterior to the second material 602 and the third material 603.

(50) As will be understood by those of skill in the art, particular embodiments of the current disclosure provide layers that are not limited in number, to their locations at the apparent thicknesses within the contact lens 600, to a symmetrical configuration, to a uniform thickness profile, or to a centered position relative to the geometric center of the contact lens 600. For example, additional layers or a deeper or shallower placement of the layers may be employed, or a regional placement may be employed. In this manner, the lens can be customized for the inclusion of a number and variety of layers and the thickness of the layers can be determined to provide desired oxygen and water transmissibilities.

(51) Various methods of fabrication may be used to create the composite film and contact lens disclosed herein. For example, the contact lens may be fabricated at least in part by molding, including cast molding and compression molding. Melt pressing and solution casting may also be implemented, at least in part, to fabricate the contact lens. Additionally, the contact lens may be fabricated at least in part by lathing.

(52) The different materials making up the material films, composite films, and/or contact lens can have different moduli. Modulus, or more specifically an elastic modulus, of a material is a measure of the material's resistance to being deformed elastically. In a particular embodiment, the modulus of the primary material films is greater than the modulus of the secondary material films. In alternative embodiment, the modulus of the primary material films is less than the modulus of the secondary material films.

(53) In addition to providing a contact lens with a minimum transmissibility of the permeant oxygen, the contact lens may also have a minimum transmissibility of a permeant such as carbon dioxide. In such a case, the layers of material film and/or thickness of the contact lens are set for a minimum carbon dioxide transmissibility, instead of or in addition to the minimum oxygen transmissibility.

(54) The same principals discussed above also provide for the delivery of a therapeutic agent. A therapeutic agent delivery device comprises a composite film, where the composite film comprises one or more layered primary material films and one or more layered secondary material films, where the composite film has a thickness, a permeability for a first permeant, and a permeability for a second permeant; where the primary material films and secondary material film each have a thickness, a permeability for a first permeant, and a permeability for a second permeant; where the thickness of the composite comprises the summed thicknesses of the primary material layers and secondary material layers, where the thickness of the primary films and the thickness of the secondary films are such that the difference between the permeability for the first permeant of the composite film and the permeability for the first permeant of the primary material films is less than the difference between the permeability for the second permeant of the composite film and the permeability of the second permeant the primary material films. In such an embodiment, the second permeant is a therapeutic substance.

(55) It should be understood that while various embodiments of the invention are described in some detail herein, the present disclosure is made by way of example only and that variations and changes thereto are possible without departing from the subject matter coming within the scope of the following claims, and a reasonable equivalency thereof, which claims are regarded as the invention.