HK1114057B - A method of the manufacture of an implantable intraocular planar/convex, biconvex, planar/concave or convex/concave lens, an open mold used for the execution of this method, and a lens made using this method - Google Patents

Description

Method for producing implantable intraocular planar/convex, biconvex, planar/concave or convex/concave lenses, open mould for carrying out the method, and lenses made using the method

Technical Field

The present invention relates to a method for producing implantable intraocular planar/convex, biconvex, planar/concave or convex/concave lenses, an open mold for carrying out the method, and lenses made using the method.

Background

Intraocular lenses are lenses that are implantable in the eye for the purpose of altering the correction. They may be implanted in various parts of the eye, such as the posterior chamber, anterior chamber or stroma (stroma). Intraocular lenses are made of materials of various hardnesses. In the case of hard materials, such as certain poly (alkyl methacrylates), in particular polymethyl methacrylates, or dehydrated hydrogels, also known as xerogels, the most common production method is lathing followed by polishing. Flexible intraocular lenses are typically produced by casting in a suitable mold. The casting was based on the following procedure: filling the mold with a liquid polymer precursor, such as a mixture of specific monomers, a molten polymer, or a liquid prepolymer having crosslinking ability; the material is subsequently converted into the solid state, which is also referred to as curing. In the case of flexible materials for intraocular lenses, the curing typically involves crosslinking, i.e. the formation of a three-dimensional covalent network, which stabilizes the shape of the lens. For example, the above network may be formed by copolymerizing a copolymeric difunctional monomer with a multifunctional crosslinking comonomer known as a crosslinking agent or crosslinker, or by additional crosslinking of the liquid polymer.

The transition from liquid to solid state is accompanied by a large or small volume shrinkage, which significantly complicates the casting of products requiring extremely high shape accuracy, such as intraocular lenses.

The casting process can be relatively easily accomplished using liquid precursors that undergo less volume shrinkage when crosslinked. An example of the liquid precursor is silicone rubber.

Current intraocular lenses are based on the crosslinking of acrylic or methacrylic polymers, however, they are typically made by cross-linking copolymerization of mixtures of acrylic and/or methacrylic monomers. Such a monomer mixture comprises at least one monomer having one polymerizable double bond representing the base monomer or monomers and at least one monomer having two or more copolymerizable double bonds representing the crosslinking comonomer or comonomers.

The base monomer forms the polymer backbone during polymerization, while the crosslinking comonomer forms covalent bridges between chains. The result of this copolymerization is the formation of a three-dimensional network which is infusible and insoluble in any solvent. The method described above is generally used in the case of hydrogels.

If, for example, the base monomer is 2-hydroxyethyl methacrylate, it copolymerizes with a small amount, usually not more than 2 mol%, of vinyl dimethacrylate as a crosslinking agent, a crosslinked poly (hydroxyethyl methacrylate) will be formed. Such hydrogels are described, for example, in US2976576 and US3220960 and are the basis for many contact lenses and various implants, including intraocular lenses.

Ophthalmic lenses are produced using a variety of forming methods, such as polymerization in a closed mold. However, closed molds are not particularly suitable for cross-linking copolymerization, which subsequently can have significant volume shrinkage up to 20 volume percent. If the volume of the closed mould cavity is constant, this shrinkage leads to a reduction in the pressure inside the mould, which has many undesirable consequences, in particular the formation of cavities, bubbles, cavities and surface defects. Shrinkage during curing is a common problem in plastic molding, which can be solved in various ways, such as gradually adding additional liquid precursor during injection molding of thermoplastic resins, by which pressure loss due to shrinkage is compensated for.

However, this technique is practically unusable in the case of crosslinking copolymerization, because a gel point, which is a state in which a three-dimensional network is generated and the flowability of the copolymerization product is prevented, is reached at a very low degree of conversion. Significant shrinkage occurs at the above gel point where no other liquid precursor can be added.

These difficulties during cross-linking copolymerizations in closed molds have led to the search for alternative casting techniques. Casting optical components such as ophthalmic lenses requires extremely good form accuracy, excellent surface quality, and material uniformity, in other words, quality that cannot be obtained without maintaining excessive pressure in the closed mold cavity. The patent literature proposes a number of solutions to this problem. One of these is casting while rotating the mould, which is well known under its original name "spin casting" and is proposed for the production of hydrogel contact lenses, for example in US patents US3660545, US4517138, US4517139, US4517140 and US 4551086. This technique is used to produce contact lenses using open concave molds having sharp edges that form the boundaries of the mold. The mold is filled with a relatively small volume of the monomer mixture, which is significantly less than the volume of the concave cavity of the mold. In this case, the page of liquid monomer mixture is always recessed below the sharp-edged plane of the mold. As the mold rotates about the vertical axis of symmetry of the mold cavity, the liquid monomer mixture will spread to form a concave shape approximating a paraboloid. The product is a convex/concave lens with a very low center thickness, which means that it is significantly lower than the sagittal depth of the mold cavity. Such shapes are particularly suitable for hydrogel contact lenses. The rotational speed of the molds used for the production of contact lenses is typically 300 to 500rpm, with the mold cavity diameter in the plane of the sharp edges of the molds typically being 13 to 17 mm.

Another known application of spin casting is the formation of parabolic mirrors for telescopes and other instruments that require accurate focusing. In these cases, the goal is to form a parabolic optical surface with a single focus of coaxial rays and no spherical distortion.

US patent 3691263 describes a different spin casting method in which the casting of the contact lens is accomplished without the use of a mold. It involves the polymerization of liquid monomers on the surface of a rotating carrier liquid, wherein the carrier liquid is immiscible with the polymerizing liquid monomers, has a higher density than the polymerizable liquid monomers, and is, for example, mercury or a concentrated salt solution.

Another improvement of the process is the use of monomer polymerization carried out at the interface of two rotating immiscible liquids, one of which has a higher density than the starting monomer and the resulting polymer and the other has a lower density than the starting monomer and the resulting polymer.

US patent 4806287 describes a method for producing lenses using hydrophilic gels. The method is based on solidifying droplets of monomer under an immiscible liquid, such as an oil, while at least the optical zone of the lens is formed between the mould and a suitably configured plunger. The alternative mentioned therein is also a mold rotation, wherein the mold rotation does not affect the optical area of the lens defined by the shape of the punches, it only affects the molded peripheral portion. For the reasons stated above, such lenses cannot be considered spin-cast lenses.

Spin casting on high specific gravity levels can also be used for casting precision catheters made of crosslinked polymers, as described in czech patent CZ 153760.

Heretofore, spin casting has not been used to produce intraocular lenses for several reasons. First, most intraocular lenses produced to date have a relatively small diameter, typically no greater than 6 mm. For the above diameters, it is estimated that centrifugal casting has only a limited effect on the shape of the lens, since the centrifugal force increases with the square of the distance from the axis of rotation. In addition, intraocular lenses are typically biconvex, or less plano-convex, and spin casting has only been used up to now for lenses that are predominantly convex/concave, such as in the case of contact lenses. Finally, currently produced intraocular lenses typically have a complex shape with a non-circular trajectory with an optical area and an integrated synapse (haptic) for centering the lens in the eye. This non-circular shape is not suitable for spin casting in open molds. For the reasons stated above, the skilled person has so far considered spin casting of intraocular lenses to be infeasible.

Heretofore, intraocular lenses have been produced using a static mold cast into an opening, wherein the meniscus formed by the liquid monomer defines the shape of one of the optical surfaces. These methods are described in US4971732, US4846832 and US 5674283. According to US4971732, a liquid monomer mixture is metered into a concave cavity having sharp edges that form the boundaries of the cavity. The material from which the mould is made is difficult to wet by the monomer mixture. The volume of the liquid monomer mixture metered into the mold must be equal to or preferably higher than the volume of the mold cavity so that the level of the liquid monomer mixture reaches the sharp edge of the mold. If the amount of liquid monomer mixture is insufficient in this regard, the liquid filling the mold cavity will shrink away from the sharp edge due to polymerization shrinkage; it is therefore not possible to obtain a high quality product in this case. It is therefore advantageous to increase the metered volume of the liquid monomer mixture and thus to obtain a higher meniscus. The excess volume of the monomer relative to the mold cavity and the resulting height of the meniscus affect the optical power of the lens. Thus, by metering various volumes of liquid monomer mixture into the cavity, a single mold can be used to produce lenses of various powers.

A typical product of the above process is a biconvex intraocular lens having a diameter of more than 9mm, a central thickness of 2.5 to 6.3mm, a flattened ellipsoidal anterior optic surface with a central radius of 7.5 to 15mm, a rotationally symmetric posterior optic surface with a central radius of 5 to 8mm, and an annular transition zone between the two optic surfaces.

This typical product has several disadvantages. First, the central thickness and total lens volume are too high for the small incision implants required by today's surgeons. Secondly, the front optical surface of a flat ellipsoid shape is disadvantageous because it has a high spherical aberration. Furthermore, since the polymerization proceeds at various rates in various portions of the monomer mixture, the surface is often deformed unevenly, and thus shrinkage is not completely uniform. This is a general disadvantage of static polymerization casting in open molds.

US4846832 describes a flexible biconvex intraocular lens with a posterior convex surface formed by a solidified meniscus, while the anterior surface has a central convex region of diameter 4 to 8 mm. The central region is surrounded by a concave surface of the relatively thin peripheral region. Thus, the front side of the lens is embossed by the mold to form a concave optical center region and a sharp rounded edge (rim) at the edge. Since the back side is formed by a solidified liquid meniscus, it may also have a flat ellipsoid shape and thus it also has a high spherical aberration. Intraocular lenses can be manufactured using the above-described method, or using silicone rubber or using a crosslinked hydrogel having a higher refractive index of 1.42 to 1.43.

US5674283 describes a disc-shaped intraocular lens with a biconvex optical zone produced in a similar manner to the previous method but produced in a different manner. The main differences are that: in the case of a lens manufactured according to US patent 5674283, the rear side of the lens is shaped with a mould cavity and the front face of the lens is shaped with a meniscus of a single body, i.e. similar to the case of a lens manufactured using the method of patent US4971732 as opposed to a lens manufactured according to the method described in US patent US 4846832. This method is an improvement of US4846832, with the difference that the optical surface created by the meniscus is used only in the central region of the lens. The method utilizes a two-part formation in which the top of the mold has a central circular window in which a meniscus of liquid monomer is formed. The diameter of the optical zone is substantially smaller than the diameter of the entire lens.

The object of the present invention is to improve the production of intraocular lenses, still used up to now, in open moulds, described in patents US4971732, US4846832 and US5674283, and thus to obtain a wider choice of the available shape and power values, an improvement in the optical quality, and an increase in the productivity of the intraocular lenses. Within the framework of the present invention, the technical prejudice in the art that centrifugal casting is not considered useful for the production of intraocular lenses has been overcome and it has surprisingly been found that contrary to this, centrifugal casting can be used to produce intraocular lenses of the desired quality under the conditions defined by the present invention. Although the centrifugal casting used within the framework of the invention was originally developed for contact lenses, the conditions for producing intraocular lenses according to the invention and the conditions used to date for producing contact lenses are completely different and cannot be deduced from each other, since the conditions suitable for intraocular lenses cannot be used for contact lenses and vice versa. The method of the invention is different from the prior art even in the technical problems to be solved. Whereas in the case of implantable intraocular lenses, the present invention solves the problem of static casting in open molds and of removing certain drawbacks thereof, rotational casting of contact lenses does not result from static casting in open molds, since contact lenses cannot be manufactured by static casting in open molds at all, and therefore, in the case of contact lenses, casting while rotating is not intended to attempt to solve the technical problems of static casting, but rather to solve a completely different series of technical problems related to shrinkage in closed molds. Within the scope of the present invention it was found that implantable intraocular lenses can be advantageously manufactured by spin casting under the conditions specified below, and that, in addition, the result of the inventive method is implantable intraocular lenses with a unique structure and useful properties.

Summary of The Invention

The subject of the present invention is a process for the preparation of implantable intraocular planar/convex, biconvex, planar/concave or convex/concave lenses made of a liquid polymer precursor capable of being transformed into a transparent solid polymer by polymerization and/or crosslinking in an open mould having a functionalized shaped inner surface separated from the remaining surfaces of the open mould by a peripheral circular sharp edge, which is not wettable or completely wettable by the liquid precursor, wherein the process comprises the following steps:

a) metering the liquid polymer precursor into the open mould in an amount such that the surface edge of the liquid precursor in contact with the inner surface of the open mould is below or reaches the peripheral circular sharp edge of the open mould and at least part of the surface of the liquid polymer precursor will protrude above the plane defined by the peripheral circular sharp edge of the open mould, or at least part of the surface of the liquid precursor is in the plane, or the entire surface of the liquid polymer precursor is below the plane, while in this case metering the liquid polymer precursor into the open mould in an amount always higher than the amount of liquid polymer precursor required to obtain a contact lens of the same diameter,

b) the open mold containing the liquid polymer precursor is rotated about its longitudinal axis at a speed at which the edge of the liquid polymer precursor surface reaches the peripheral circular sharp edge of the open mold, the liquid polymer precursor is in contact with the entire inner surface of the open mold, and the surface of the liquid polymer precursor is located in the plane defined by the peripheral circular sharp edge, or above or below this plane,

c) exposing the liquid polymer precursor to conditions under which the liquid polymer precursor is capable of being converted to a transparent solid polymer by polymerisation and/or cross-linking;

d) continuing to rotate the open mold at said speed at least until the surface edge of the polymerized and/or crosslinked liquid polymer precursor reaches the peripheral circular sharp edge of the open mold, even if the rotation of the mold is slowed or stopped in the meantime;

e) then optionally slowing or stopping the rotation of the open mold;

f) exposing the contents of the open mould to the above conditions, the conversion of the solid polymer into a transparent state by polymerisation and/or crosslinking during the exposure continuing at least until said conversion is obtained,

g) the implantable intraocular lens is removed from the open mold.

Preferably, the liquid polymer precursor comprises at least one monomer having at least one free-radically polymerizable double bond.

Preferably, the free radical polymerization is initiated by cleavage of an initiator comprising a peroxy bond or an azo bond.

Preferably, the free radical polymerization is initiated using free radicals generated under the action of radioactive or electromagnetic radiation or under the action of accelerated electrons.

Preferably, the monomer having at least one free-radically polymerizable double bond is a derivative of acrylic acid and/or methacrylic acid.

Preferably, at least one of the derivatives of acrylic acid and/or methacrylic acid is an ester of a polyol with at least two molecules of acrylic acid and/or methacrylic acid.

Preferably, at least one of the derivatives of acrylic acid and/or methacrylic acid is a salt of acrylic acid or methacrylic acid.

Preferably, at least one of the monomers having at least one free-radically polymerizable double bond comprises a functional group capable of absorbing electromagnetic radiation in the range of 190 to 500nm, advantageously in the range of 300 to 400 nm.

Preferably, the group capable of absorbing electromagnetic radiation is derived from a benzophenone or a benzotriazole.

Another subject of the invention is an open model for carrying out the above method, the principle of which is based on the fact that it comprises an open concave cavity defined by a functionalized shaped internal surface, which cavity ends with a circular peripheral sharp edge lying in a plane perpendicular to the longitudinal axis of the open concave cavity and having a diameter of 5 to 10 mm.

Preferably, the radius of curvature of the open concave cavity increases from a lowest value near the longitudinal axis of the open concave cavity in a direction toward the peripheral circular sharp edge of the open concave cavity.

Preferably, the functionalized shaped concave inner surface of the open concave cavity has a shape defined by a rotation of a partial conical section line (a continuous section) along a longitudinal axis of the open concave cavity.

The section line of the cone is preferably formed by the formula Y ═ a + (a/b) · (b)²+X²)^0.5Wherein a ═ R_c·(1+h)，R_cIs the central radius of curvature and h is a parameter defining the asphericity, chosen between-1 and + infinity.

The parameter h defining the asphericity is preferably chosen between-0.75 and + 1.

Center radius of curvature R_cSelected from between 2 and 20mm, preferably between 2.5 and 5 mm.

The peripheral sharp edge is preferably circular with a diameter of 7 to 9 mm. The open concave cavity preferably passes through the upper portion of the open mold above the intermediate circular edge, which is circular and lies in a plane parallel to the plane in which the peripheral circular sharp edge lies, into a transitional open cylindrical or frusto-conical cavity defined between the peripheral circular sharp edge and the intermediate circular edge.

The preferred height of the transition opening cylindrical or frusto-conical cavity is 0.01 to 0.2mm, more preferably 0.03 to 0.08 mm.

The preferred volume of the open concave cavity, or alternatively the combined volume of the open concave cavity and the transition open cylindrical or frusto-conical cavity, is from 15 to 175 μm, more preferably from 25 to 55 μm.

According to the invention, the mould is preferably made of a plastic material that is not wettable or completely wettable by the liquid polymer precursor.

Preferably, the inventive mold is made of polyolefin.

The subject of the invention is also implantable intraocular planar/convex, biconvex, planar/convex or convex/concave lenses which can be produced by the process according to the invention described above or can be produced in the open mould according to the invention described above.

Drawings

A preferred cross-section of the inventive die is shown in fig. 1, with a cavity formed by the combination of an open concave cavity and a transition open cylindrical cavity;

FIG. 2 shows a partial cross-section of another preferred open mold of the present invention having a cavity formed by the combination of an open concave cavity and a transition open frustum;

FIGS. 3A to 3C show schematic views of spin casting with liquid polymer precursor at various levels of liquid filling the open mold in the open mold of the present invention;

FIG. 4 shows a schematic view of spin casting at various open mold speeds in the open mold of the present invention;

figure 5 illustrates a preferred special open mold of the present invention.

Detailed Description

Intraocular lenses can be produced from various crosslinked polymers according to the present invention. Within the scope of the present invention, an advantageous polymer is one that has a softening temperature below body temperature when the polymer is in equilibrium with the intraocular fluid. The polymer may be silicone based, for example as described in US 5519070. Furthermore, the polymer may also be a hydrophobic and hydrophilic acrylic or methacrylic polymer, polyurethane or polyurea as described in patent US 6165408. Particularly advantageous are hydrogels suitable for ophthalmic use, for example US2976576, US3220960, US5224957, US4775731, US4994083, US4997441, US5002570, US5158832, US5270415, US5910519, US5698636, US5391669, US5674283, US5158832 and US6372US 815. Of these, particularly suitable are covalently crosslinked copolymers comprising acrylic acid and/or methacrylic acid and derivatives thereof, such as esters, amides or salts. Most suitable are crosslinked hydrophilic methacrylate copolymers.

At least a portion of the copolymer is formed with a copolymerizable monomer that absorbs radiation having a wavelength of between 290 and 500 nanometers, preferably between 300 and 400 nanometers. Such monomers based on, for example, benzophenone or benzotriazole derivatives are known in the art. Examples are copolymers which absorb ultraviolet radiation as disclosed in US 5133745.

Curing of the liquid precursor may be accomplished by polymerizing a mixture of base monomers and crosslinking monomers. Suitably, the polymerization is a free radical polymerization and is initiated using a commonly used free radical initiator or photoinitiation mechanism. Free radical polymerization can be initiated with electromagnetic radiation in various regions of the spectrum, for example in the visible, ultraviolet, x-ray or gamma radiation regions. The free radicals may even be generated by absorption of free electrons from beta radiation or electrons accelerated by an electric field. Curing may be carried out by crosslinking a liquid polymer precursor, such as a reactive silicone prepolymer or a polyvinyl alcohol solution. Photoinitiated polymerization or crosslinking is a particularly advantageous process and is described, for example, in US patents 6190603 and US 5224567. The metering of the liquid precursor is desirably carried out with an accuracy of more than 1mg, preferably with an accuracy of more than 0.1 mg. Rotation of the open mold containing the liquid polymer precursor can be achieved using a variety of techniques and a variety of apparatus disclosed in US patents US3660545, US4517138, US4517139, US4517140 and US 4551086. If some of the components of the precursor polymer mixture are relatively volatile, evaporation can be limited by maintaining the mold with the liquid precursor in a closed system with very small gas phase spaces while curing is taking place. Such spin casting methods and devices suitable for lenses made from volatile monomers are described in US 4680149.

An advantageous open mold design for carrying out the method of the invention is shown in fig. 1. The open mold 1 comprises: first, an open concave cavity 2 defined by a functionalized shaped concave inner surface 3 and an intermediate circular edge 4, and second, a transitional open cylindrical cavity 5 defined by a functionalized shaped cylindrical inner surface 6, an intermediate circular edge 4, and a peripheral circular sharp edge 7. The inserted circular edge 4 and the peripheral circular sharp edge 7 are both located in a plane perpendicular to the longitudinal axis 8 of the cavity of the open mould 1. The distance between these mutually parallel planes determines the height Hv of the transit-opening cylindrical cavity 5; the sagittal depth S of the cavity of the open mould 1 is determined by the distance of the plane in which the peripheral circular sharp edge 7 lies from the cross section of the longitudinal axis 8 of the cavity of the open mould 1 with the functionalized shaped concave inner surface 3; and the diameter of the circle formed by the peripheral circular sharp edge 7 determines the peripheral diameter D of the cavity of the open mould 1. The body of the open mould may be made of a variety of materials, however the most advantageous material is plastic. Of the plastics, polyolefins, such as polyethylene or polypropylene, are most advantageous. The material used to make the open mold is selected so that it is not readily wetted by the liquid polymer precursor. The wetting angle is preferably above 30 °, more preferably above 90 °. The open mold may preferably be designed for use alone and manufactured by injection molding.

The functionalized shaped surfaces of the open mold cavity do not necessarily have to be symmetrical. In principle it may have any desired shape as long as the inserted circular edge 4 and the peripheral circular sharp edge 7 are truly circular. The open mold cavity may be formed by a combination of spherical and cylindrical flats, such as are required to compensate for astigmatism. Most commonly, however, a rotationally symmetric surface having the same axis of symmetry as the longitudinal axis 8 of the open mould cavity is used. Most advantageous is a face formed by rotating a portion of a conical section line comprising a circle, ellipse, paraboloid, hyperbola, or various combinations thereof. The various portions of the functionalized shaped surface of the open mold cavity may be formed by rotating various curves. It may thus be, for example, the central part of the inner shaping surface of the open mould cavity formed by a spherical surface, while the remaining part of the inner shaping surface facing the edge of the open mould cavity may be formed by a truncated cone surface. Another example is a surface consisting of concentric portions with various curvatures, enabling the creation of bifocal or multifocal intraocular lenses.

Within the scope of the invention, it is most advantageous to have a smooth surface formed by rotating a continuous curve having the lowest radius of curvature in the vicinity of the longitudinal axis 8 of the open mould cavity and whose radius of curvature increases progressively with increasing distance from said longitudinal axis 8. The above-mentioned advantageous surfaces may be formed by rotating hyperbolas, which may be approximated using orthogonal coordinates X and Y in the following formula:

Y＝-a+(a/b)·(b²+X²)^0.5，

wherein the content of the first and second substances,

a＝R_c·(1+h)²

b＝R_c·(1+h)，

and Rc is the center radius of curvature and h is a parameter defining the asphericity of the surface. The parameter h may be selected from between-1 and + infinity. When H is close to-1, the curve described by equation (1) is close to a straight line, and when H is close to + infinity, it is close to a circle. Within the scope of the invention, the most advantageous h value is-0.75 to +1 when the resulting surface is predominantly aspherical and its refractive power decreases from its maximum central value to its minimum peripheral value. Intraocular lenses formed under these conditions are multifocal. In the case of a reduced value of the parameter h, asphericity and multifocal properties are enhanced. Molds for spin casting contact lenses typically have a spherical cap shaped cavity, and the value of the parameter h in the case of contact lenses approaches infinity. This proves that the known molds for contact lenses and the molds of the invention for implantable lenses are not interchangeable even from this point of view.

Center radius of curvature R_cThe value of (A) is chosen between 2 and 20mm, preferably from 2.5 to 5 mm. It must be emphasized once again that molds with cavities of this shape are not at all usable for the casting of contact lenses, whereas, conversely, the shape of the open mold cavity for contact lenses is not usable for the production of the intraocular lenses of the invention.

The edge shape of the open mold cavity of the present invention is important to both the manufacturing process and the resulting implantable intraocular lens function. An advantageous shape of the edge of the cavity of the open mould 1 according to the invention is depicted in fig. 2, which depicts a partial cross-section of the edge of the open mould. In fig. 2, it is evident that the open mold 1 cavity is constituted by: first, an open concave cavity 2 defined by the functionalized shaped concave inner surface 3 and its central circular edge 4, and second, a transitional open frustoconical cavity 9 defined by the central circular edge 4, the peripheral circular sharp edge 7, and the functionalized shaped frustoconical inner wall 10. In FIG. 2, the slope of the functionalized concave shaped surface 3 and the functionalized frustro-conical inner wall 10 is defined by the angle α₁And alpha₂Determine the angle alpha₁Advantageously in the range 75 ° to 175 °, more advantageously 90 ° to 105 °, while the angle α is₂Advantageously in the range of 60 ° to 135 °, more advantageously in the range of 75 ° to 10 °5 degrees. The peripheral diameter D of the cavity ranges from 5 to 10mm, advantageously from 7 to 9 mm. The sagittal depth S of the cavity is advantageously in the range 0.75 to 5mm, more advantageously 1 to 2.3 mm.

It must be emphasized again that an open mold of the above-mentioned dimensions is completely unsuitable for rotational casting of contact lenses, since the peripheral diameter of the molds used for contact lens production is typically 13 to 17 mm. Cavity volume V of open die_cThe volume can be calculated as the space defined by the functionalized shaped inner surface of the open mold cavity and the plane of the circular sharp edge of the periphery of the open mold. In the case of the open mould according to the invention, the volume V of the cavity_cAdvantageously 15 to 175. mu.l, more advantageously 25 to 55. mu.l. Open molds for contact lens production having higher cavity volumes V_cAnd usually 200 to 600. mu.l.

Depending on the geometry of the mold, the metered volume V of liquid polymer precursor₁May vary within wide ranges, but typically it ranges from about 10 to about 100. mu.l. If V₁＜V_cThe liquid polymer precursor does not reach a peripheral circular sharp edge in the static mold. In this case, it is necessary to rotate the open mold to wet the entire functionalized shaped inner surface of the open mold cavity. However, shrinkage of the polymer precursor during curing, which typically takes up about 20% by volume, will cause the liquid in the open mould to withdraw from the peripheral circular sharp edge. Therefore, this would render the shape of the intraocular lens useless. This unwanted phenomenon can be prevented by rotating the open die at a sufficiently high rotational speed. Shrinkage during curing can be characterized by a shrinkage factor C, which is the specific gravity (d) of the polymer precursor before and after curing_mAnd D_p) The proportion of (A): c ═ d_m/d_p。

The value of the shrinkage factor C may vary widely between values of about 0.8 to close to 1. In summary, it is desirable for the metered volume V of the liquid polymer precursor₁And volume V of the cavity_cIn a specific ratio. The filling ratio Z is V₁/V_cIn the range of about 0.75 to about 2, advantageously in the range of about 0.95 to about1.5. By way of comparison, the filling ratio used in the case of contact lenses is Z < 0.5, typically a value between 0.05 and 0.2. It can thus be stated that the filling ratio values for the inventive implantable lenses are higher than those for the production of contact lenses using spin casting, whereas the filling ratio values normally used for contact lenses are not usable in the inventive method for the production of intraocular lenses.

Due to the uneven polymerization process, the surface quality of the polymer formed in the open static mold is generally poor, which leads to uneven shrinkage and thus surface deformation. This is particularly problematic in the case of cross-linking polymerization, where the polymerization rate increases significantly with viscosity, i.e. reaction conversion. This increase in reaction rate is particularly acute at the gel point where a three-dimensional continuous network just forms, which is known as the so-called Trommsorf Effect (Trommsorf Effect). This undesirable phenomenon is significantly limited by the rotation of the die, even at extremely low rotational speeds. On the one hand, the speed is balanced over all different parts of the cavity, and on the other hand, the rotation helps to stabilize the shape of the liquid surface. Both of these lead to a great improvement in the quality of the product surface as a result of spin casting, rather than static casting. The centrifugal force created by the rotation of the mold spreads the liquid polymer precursor in a direction away from the longitudinal axis of the open mold cavity and towards the edges of the open mold until the level edges of the liquid polymer precursor reach and remain in contact with the peripheral circular sharp edge of the open mold until the polymer precursor solidifies, i.e. until the viscosity of the mold charge reaches a viscosity at which the precursor is practically no longer flowing and remains in contact with the peripheral circular sharp edge, even in the event that the rotation of the mold is stopped. In the case of cross-linking polymerization, this state already occurs at relatively low conversions, for example at conversions of 3 to 5%.

This is diagrammatically represented by fig. 3A to 3C, in which the open mold of the present invention has been described in detail with reference to fig. 1. The cavity of the open mold is created by the combination of an open concave cavity and a transition open cylindrical cavity.

FIG. 3A shows the case of a filling ratio Z < 1, in which the cavity volume V of the open mold is_cHigher than the metered volume V of liquid polymer precursor₁. The liquid polymer precursor occupies a static surface S in the open static mold, and a surface R of the mold as it rotates at a speed such that the liquid surface of the liquid precursor reaches the peripheral circular sharp edge. As is evident from fig. 3A, the initial convex meniscus of the liquid changes to a concave surface. Provided that Z is V₁/V_c< 1, the rotational speed of the open mold must be relatively high and the anterior surface of the produced intraocular lens will be a concave surface having negative optical power. With increasing rotational speed of the open-end tool, with increasing peripheral diameter D of the open-end tool cavity, with decreasing shrinkage factor C and with decreasing filling ratio Z-V₁/V_cThe concavity of the anterior wall of the intraocular lens will increase and the overall positive refractive power of the lens will decrease.

FIG. 3B shows the case where the filling ratio Z is 1, so that the metered volume V of liquid polymer precursor₁Is completely equal to the cavity volume V of the open mold_c. In this case, a static planar surface S will be formed in the static open mold. During gentle rotation about the longitudinal axis of the open mold, the rotating surface R has a slightly concave meniscus in the center of the surface and the edge of the surface slightly beyond the peripheral circular sharp edge of the open mold. In this case, the rotation surface R has an inflection point. The rotational speed of the open die is selected so as to ensure contact of the liquid polymer precursor with the peripheral circular sharp edge but in the process the liquid polymer precursor does not overflow the peripheral circular sharp edge. The rotational speed of the selected open die will depend on a number of parameters, among which in particular the volume V of the cavity_cMetering volume V of liquid Polymer precursor₁Specific gravity of the liquid precursor before and after curing, surface tension of the liquid precursor, and wetting angle between the functionalized shaped interior wall and the liquid polymer precursor of the open mold cavity. During polymerization, the concavity of the meniscus will become more pronounced due to shrinkage and thereby form a slightly convex/concave implantable lens.

At a filling ratio Z ═ V₁/V_cIf > 1 and Z · C is 1, then at low rotational speeds of the open mold an intraocular flat/convex mirror can be obtained with an anterior facet of approximately zero refractive power. An increase in the rotational speed of the open mold will result in a concave anterior wall of the intraocular lens which contributes negatively to the overall refractive power. These conditions are specific to intraocular lenses because they cannot occur during contact lens production.

With increasing opening die speed, with increasing peripheral diameter D of the cavity, with decreasing shrinkage factor C, and with filling factor Z ═ V₁/V_cThe anterior surface of the intraocular lens will decrease in convexity and possibly increase in concavity, which will also decrease its positive refractive power.

FIG. 3C shows the case where the filling ratio Z > 1, whereby the metered volume V of liquid polymer precursor₁Volume V higher than the open mold cavity_c. Even in this case the liquid polymer precursor does not overflow beyond the peripheral circular sharp edge of the open mould if the mould surface is not or at least poorly wetted by the liquid polymer precursor. A convex meniscus will form and the liquid polymer precursor will reach the static surface S. As long as the condition Z.C > 1 is maintained, a biconvex intraocular lens will be formed by polymerization or crosslinking. During the rotation of the open mould along the longitudinal axis, the liquid surface of the liquid polymer precursor will change its profile and will reach the rotating surface R, whereas at higher rotational speeds of the open mould a planar or even slightly concave central zone will be formed. In this case, the liquid surface of the liquid polymer precursor at a low rotation speed of the open die is substantially formed into a flat ellipsoid having the high spherical aberration already stated as it is at zero rotation speed of the open die. Increasing the rotational speed of the open mold will result in a decrease in the convexity of the central zone of the intraocular lens and may even result in a flatness or concavity of the central zone of the intraocular lens. This results in a reduction of the spherical distortion of the lens in this critical central region.

This is schematically depicted in fig. 4, in which there is an open mold substantially as already described in fig. 2The picture, and the cavity of the open mold is formed by the combination of an open concave cavity and a transition open frustum. At low rotational speeds of the open mold, the surface of the liquid polymer precursor will appear as a rotating surface R₁At medium rotational speed of the open die is the surface of revolution R₂At high rotational speed of the die is the surface of revolution R₃. The highest usable open die rotation speed is limited by the centrifugal force at the edge of the open die cavity, which cannot exceed the cohesive force of the liquid polymer precursor due to its surface tension. If this highest usable open mold rotational speed is exceeded, it will cause the liquid polymer precursor to overflow the peripheral circular sharp edge and the contents of the mold will become unusable. The rotational speed of the open-die at which the overflow of liquid polymer precursor occurs is a critical parameter, the value of which is specific for each given individual open-die and each given specific polymer precursor.

Rotation during casting in an open mould yields a number of advantages. In particular, it improves the filling of the open mould with liquid polymer precursor in the central circular concave edge region. Because the material from which the mold is made is not readily wetted by the liquid polymer precursor, and this poor wettability is required for maintaining a positive meniscus with a peripheral circular sharp edge, the open mold region in the inserted circular edge region has a tendency to trap bubbles during static casting, which prevents the production of a continuous sharp intermediate convex edge in the manufactured intraocular lens. This intermediate convex edge formed by the intermediate circular edge of the open mould cavity is important for the function of the intraocular lens, since it prevents the migration of cells along the lens and limits the occurrence of the phenomenon known under the acronym PCO (posterior capsular opacification; posterior capsular opacification after implantation), which will be described in more detail below. The rotation of the open mold creates a centrifugal force that acts on the functionalized inner surface of the cavity and thus helps force the gas out with the liquid precursor in this region. Thus, spin casting can form sharper intraocular lens intermediate edges than in the case of lenses manufactured by static casting. Contact lens molds do not have an inset rounded edge at all, because in the case of contact lenses, a sharp inset edge of the corresponding lens is highly undesirable.

Furthermore, the rotation of the open mold improves the quality of the peripheral edge of the intraocular lens, which is formed by the peripheral circular sharp edge of the open mold cavity and is required for the biocompatibility of the intraocular lens. The liquid polymer precursor generally has a tendency not to reach completely the peripheral circular sharp edge of the open mould, which occurs in particular at lower values of the filling ratio Z and at low wettability of the material from which the open mould is made. This results in the formation of an irregular jagged peripheral edge of the intraocular lens that is not allowed for the desired function of the intraocular lens. The centrifugal force caused by the rotation of the mould, acting on the functionalized shaped inner surface of the open mould cavity, will push the entire edge of the liquid polymer precursor surface to the position of the peripheral circular sharp edge of the open mould, which contributes in a decisive way to the achievement of the required quality of the peripheral edge of the intraocular lens, even at low rotational speeds of the open mould.

Rotation of the open mold also has a positive effect on the shape of the meniscus, as it moves portions of the liquid polymer precursor from the central zone into the surrounding zones, and thus flattens the central optical zone of the anterior side of the intraocular lens. This reduces the spherical aberration of the anterior face of the intraocular lens, particularly in the critical central optical zone.

Rotation of the open mold changes the central curvature of the anterior face of the intraocular lens and thus also its optical power. Based on this, one type of open mold can be used to manufacture intraocular lenses of various refractive powers, which reduces manufacturing costs.

The rotation of the open mold also improves the optical quality of the anterior side of the lens, as it creates more uniform initiation conditions, particularly in the case of photoinitiation, which thus prevents uneven shrinkage of the contents of the open mold, which would result in surface irregularities in the manufactured intraocular lens.

The rotational speed of the open mould may be varied at various stages of the casting process. For example, the rotation may be slower at the beginning and the axis of rotation need not be vertical, which will achieve more uniform wetting of the functionalized shaped inner surface of the open mold cavity by the liquid polymer precursor, and will facilitate uniform spreading along the functionalized shaped inner wall of the open mold cavity. The rotation may then be accelerated to obtain the desired meniscus shape, or may be slowed down and may even be stopped in case the entire meniscus edge of the liquid polymer precursor reaches the peripheral circular sharp edge of the open mould and the increased viscosity of the liquid polymer precursor by polymerisation and/or cross-linking has stabilized this position of the liquid polymer precursor meniscus edge.

Spin casting can be performed in a variety of open molds as described in, for example, US patents US4517138, US4517139, US4517140, US5300262, US5435943, US5395558, US5922249 and US5674283 and with improved equipment for spin casting contact lenses.

Upon curing the liquid polymer precursor, the intraocular lens is nearly complete. In contrast to other manufacturing methods for manufacturing intraocular lenses, the present method does not require machining, such as lathing, milling, filing and polishing, of the resulting intraocular lens. According to the present invention, an intraocular lens can be manufactured in substantially one manufacturing step without touching a human hand. This is an important advantage of the method of the invention, as it improves its biocompatibility and reduces the possibility of damaging the surface or contaminating the intraocular lens.

The material from which the open mold is made may be selected so that it has low adhesion to the resulting crosslinked polymer. In this case, the manufactured intraocular lens can be removed from the mold without prior hydration. However, this poses a risk to the intraocular lens, particularly its delicate edges, which may be easily damaged due to the fragility of the dehydrated material. It would therefore be advantageous to hydrate the finished intraocular lens directly in the open mold in which it is made. Hydration will soften the intraocular lens and in addition it will reduce its adhesion to the functionalized shaped inner wall of the open mold cavity so that the intraocular lens can be separated from the mold itself.

The intraocular lens may then be freed of residual monomers and other impurities by extraction, using conventional methods developed for various types of implantable materials. The intraocular lens may also be subjected to chemical modification of its surface to further improve its properties such as biocompatibility and adhesion to tissue, among others. One such surface modification may be partial surface hydrolysis using basic or acidic catalysts as described in, for example, US patents US3895169, US4997441, US5080683, US5158832 and US 5939208.

The intraocular lens is finally packaged and sterilized by a suitable method, such as steam sterilization.

The method of the present invention may be used to manufacture various types of implantable intraocular lenses, such as intraocular lenses designed to be implanted in the posterior chamber of the eye, intraocular lenses designed to be implanted in the anterior chamber of the eye, or intraocular lenses designed to be implanted in the stroma. The intraocular lens described above can be manufactured using various types of crosslinked polymers. A particularly advantageous implantable lens that perfectly exploits the advantages offered by the present invention and thus offers a patient a large number of advantages at the same time, is characterized by at least some of the following characteristics.

The optical zone has a large diameter, typically 6 to 9 mm. A larger optical area has greater visual advantages, particularly at night, when the iris enlarges and the edge of the small optical area falls into the optical path in a lens made in the prior art, causing reflections, glare from too much light, loss of contrast, or other undesirable effects.

Aspheric multifocal optics have maximum positive power in the middle, gradually decreasing in the direction to the periphery. Such optics compensate for spherical distortion, have a high depth perception, and can produce pseudo-accommodation, especially for accommodation of distance vision under poor lighting conditions.

The smooth, continuous convex posterior side of the intraocular lens fits well into the posterior capsule of the original lens. This helps keep the posterior capsule naturally taut and reduces the incidence of posterior capsule opacification after implantation.

The entire surface of the intraocular lens, except for the peripheral edge and possibly the intermediate edge, is continuous, i.e. without discontinuities and ridges. This improves the optical properties and biocompatibility of the lens.

The sharp and uninterrupted intermediate bulge of the intraocular lens in contact with the posterior capsule limits cell migration into the space between the lens and the capsule, and therefore it reduces the incidence of opacification of the posterior capsule after implantation.

Axial deformability of intraocular lenses. Because of its shape, the intraocular lens can be deformed with the anterior back pressure of the internal structure of the eye containing the ciliary body, zonules and vitreous body, thus changing the curvature of its surface and making it possible to simulate the natural accommodation of the eye. Other prior art intraocular lenses of other shapes do not have such a capability and must depend on their displacement in the anterior-posterior direction; the pseudoregulatory capacity is therefore significantly poorer in this case.

The liquid has a relatively high water content at equilibrium within the eye. Under these conditions, the water content is higher than 30% by mass and advantageously higher than 40% by mass. The high water content enables dehydration during deformation and therefore creates a refractive index gradient, which further increases the optical power and contributes to spurious accommodation. The high water content also reduces the surface reflectivity of the lens, increases its biocompatibility, and in a partially or fully dehydrated state, enables its implantation through a smaller surgical opening.

The hydrogel of the poly (hydroxyethyl methacrylate) type comprises carboxyl groups, in particular the crosslinked copolymer comprises 2-hydroxyethyl methacrylate and methacrylic acid. The content of carboxyl groups is advantageously from 0.25 to 7 mol%, particularly advantageously from 0.3 to 3 mol%. Even though methacrylic acid is generally considered undesirable for contact or intraocular lenses because it binds Ca²⁺And cause calcification, the exact opposite is shown within the scope of the invention. The carboxyl group was found to inhibit calcification, which may be at a certain pointThese are observed in hydrogels, and overall they improve the biocompatibility of the hydrogels. The carboxyl group may be incorporated into the hydrogel during its preparation, during copolymerization of the base monomer with acrylic or methacrylic acid, or it may be generated in the already completed hydrogel by utilizing a partially hydrolyzed ester group. The hydrolysis may be catalyzed by an acid or base.

In the following part of this description, the invention will be further elucidated using examples of its implementation. These examples are intended to illustrate the invention only and they do not in any way limit the scope of the invention, as it is clearly defined by the claims and the content of the present description.

Examples

Example 1 (comparative)

For the production of intraocular lenses, an open mold is used, which is schematically depicted in cross-section in fig. 5 and has the following parameters:

diameter D of 7.75mm at edge

Sagittal depth S is 1.34mm

Center radius of curvature Rc of 3.50mm

Radius of curvature other than center, Rmc, 9.10

The height Hv of the transition opening cylindrical cavity is 0.05mm

The angle alpha 1 is 135 deg.,

the angle alpha 2 is 90 deg.,

the cavity volume Vc is 37.1 mul,

and a monomer solution having the following composition by weight:

98.6 percent of acrylic acid-2-hydroxymethyl,

0.25 percent of ethylene glycol dimethacrylate,

Diethylene glycol dimethacrylate 0.1%,

0.1 percent of triethylene glycol dimethacrylate,

0.4% of methacrylic acid, and

diisopropyl carbonate (diisopropopyralcarbonate) 0.5%

The base monomer mixture was mixed with glycerol in a ratio of 9 weight units of monomer mixture to 1 weight unit of glycerol. After purging the resulting monomer mixture with argon for 2 minutes, 45. mu.l of the above monomer mixture was filled into the above-defined open mold cavity. The open mold with the monomer mixture was then heated to 70 ℃ without rotating the open mold for 6 hours. The resulting hard dry gel intraocular lens is inspected prior to removal from the open mold. The central part of the meniscus thereof is partly concave and slightly corrugated due to the effect of the contraction. The corrugations are not uniform and have concentric circular or accordion-like forms. The edge of the intraocular lens is somewhat uneven and partially deformed, and has air bubbles introduced. The intraocular lens was swelled in the open mold with a 1% sodium bicarbonate solution, then removed from the open mold and extracted 10 times in an excess of 0.9% sodium chloride solution. After the last extraction, the water content inside the intraocular lens was 42 wt% and in the homogeneously swelled intraocular lens, the dimensions were as follows: the diameter is 8.9mm, and the central thickness is 1.4 mm.

The light intensity of the intraocular lens was measured on a NIKON PL2 instrument, during which process the intraocular lens was immersed in an isotonic saline solution and under a 3mm pore size. Even at the best available intraocular lens focus, the measurement cross-hair is blurred due to the deformation of the optical surface of the intraocular lens, and thus cannot be measured with sufficient accuracy. The best estimate of refractive power is +15 diopters.

Example 2 (inventive)

The procedure of example 1 was repeated, however, without adding glycerol to the base monomer mixture and during the first hour of polymerization, the open mold with the monomer mixture was rotated at 30rpm, then the rotation of the mold was stopped and the polymerization was continued under static conditions for an additional 6 hours. Due to the above polymerization, the meniscus of the monomer mixture solidified into a smooth micro-concave surface after only one hour and did not change even after the subsequent final polymerization (finish polymerization) completed under a non-rotating open mold. The edges of the intraocular lens thus obtained were sharp and well defined, with no visible defects at a magnification of 20 x. The intraocular lens has a hydrated state diameter of 9.4mm and a central thickness of 1.6 mm. The refractive power of the intraocular lens is easy to measure and the focusing pattern is clear and unambiguous. The refractive power is +14.75 diopters.

Example 3 (inventive)

The monomer mixture of example 1 was adjusted so that its glycerol content was increased to 20% by mass and 35. mu.l of this mixture was metered into the open mold cavity. At room temperature and with the inclination of the axis of rotation at 30 ° to the vertical, the rotational speed of the open die was first set at 5rpm, and then the speed was maintained for 5 minutes. The temperature was then raised to 70 ℃ and the spindle was changed to the vertical position and the rotation speed was increased to 360 rpm. The surface edge of the monomer mixture rises to the peripheral circular sharp edge of the open mold and the open mold is rotated under these conditions under a protective nitrogen atmosphere for 6 hours. The other process steps are the same as the corresponding steps described in example 1. The hydrated intraocular lens thus obtained had a convex/concave shape with a diameter of 8.5mm, a sagittal depth of 1.2mm, and a diopter value of +12.5 diopters.

Claims (20)

1. A process for the preparation of an implantable planar/convex, biconvex, planar/concave or convex/concave lens made of a liquid polymer precursor, wherein said liquid polymer precursor is capable of being transformed into a transparent solid polymer state by polymerization and/or crosslinking in an open mould, said mould having a functionalized shaped inner surface separated from the remaining surface of the open mould by a peripheral circular sharp edge, which functionalized shaped inner surface is not wettable or completely wettable by said liquid precursor, wherein:

a) metering said liquid polymer precursor into the open mould in an amount such that the edge of the surface of the liquid precursor in contact with the inner surface of the open mould is below or reaches the peripheral circular sharp edge of the open mould and at least part of the surface of said liquid polymer precursor will protrude above the plane defined by the peripheral circular sharp edge of the open mould, or at least part of the surface of said liquid precursor is in this plane, or the entire surface of said liquid polymer precursor is below this plane, while in this case the liquid polymer precursor is metered into the open mould in an amount which is always higher than the amount of liquid polymer precursor required to obtain a contact lens of the same diameter,

b) the open mould containing the liquid polymer precursor is then rotated about its longitudinal axis at a speed at which the edges of the liquid polymer precursor surface reach the peripheral circular sharp edge of the open mould, the liquid polymer precursor is in contact with the entire inner surface of the open mould, and the surface of the liquid polymer precursor is in the plane defined by the peripheral circular sharp edge, or above or below this plane,

c) exposing the liquid polymer precursor to curing conditions under which the liquid polymer precursor is capable of being converted to a transparent solid polymer by polymerisation and/or crosslinking;

d) continuing to rotate the open mold at said speed under said curing conditions at least until the surface edge of the polymerized and/or crosslinked liquid polymer precursor reaches the peripheral circular sharp edge of the open mold, even if the mold rotation slows or stops;

e) then optionally slowing or stopping the rotation of the open mold;

f) the exposure of the contents of the open mould to the above-mentioned curing conditions is continued at least until the transition is obtained,

g) the implantable lens is removed from the open mold.

2. The method of claim 1, wherein the liquid polymer precursor comprises at least one monomer having at least one polymerizable double bond by free radical polymerization.

3. The method of claim 2, wherein the free radical polymerization is initiated by cleavage of an initiator comprising a peroxy bond or an azo bond.

4. The process of claim 2, wherein the free radical polymerization is initiated by free radicals generated under the action of radioactive or electromagnetic radiation or under the action of accelerated electrons.

5. The method of claim 2, 3 or 4, wherein the monomer having at least one free radically polymerizable double bond comprises a derivative of acrylic acid and/or methacrylic acid.

6. The method of claim 5, wherein at least one of the derivatives of acrylic acid and/or methacrylic acid is an ester of a polyol with at least two molecules of acrylic acid and/or methacrylic acid.

7. The method of claim 5, wherein at least one of the derivatives of acrylic acid and/or methacrylic acid is a salt of acrylic acid or methacrylic acid.

8. The method of claim 2, wherein at least one of the monomers having at least one polymerizable double bond by free radical polymerization comprises a functional group capable of absorbing electromagnetic radiation in the range between 190 and 500 nm.

9. The method of claim 8, wherein at least one of the monomers having at least one polymerizable double bond by free radical polymerization comprises a functional group capable of absorbing electromagnetic radiation in the range between 300 and 400 nm.

10. The method of claim 8, wherein the functional group capable of absorbing electromagnetic radiation is derived from a benzophenone or a benzotriazole.

11. An open mold for carrying out the method of claim 1, wherein it comprises an open concave cavity defined by a functionalized shaped inner surface, the inner surface terminates in a circular peripheral sharp edge lying in a plane perpendicular to the longitudinal axis of the open concave cavity and having a diameter of 5 to 10mm, wherein said open concave cavity passes through the upper portion of the open mold above the intermediate circular rim into a transition open cylindrical or frusto-conical cavity defined between the peripheral circular sharp edge and the intermediate circular rim, wherein the central circular edge is circular and lies in a plane parallel to the plane of the peripheral circular sharp edge, and, wherein the functionalized shaped inner surface of the open concave cavity has a shape defined by a rotation of a portion of a tapered section line along a longitudinal axis of the open concave cavity, the tapered section line being represented by the formula Y ═ a + (a/b) × (b).²+X²)^0.5Wherein a ═ R_c·(1+h)²And b ═ R_c(1+ h) wherein R_cIs the central radius of curvature and h is a parameter defining the asphericity selected from the range-0.75 to + 1.

12. The open mold of claim 11, wherein said center radius of curvature R_cSelected from between 2 and 20 mm.

13. An open mold according to claim 12, wherein said central radius of curvature R_cSelected from between 2.5 and 5 mm.

14. An open mould according to claim 11, wherein said peripheral circular sharp edge has a circular shape with a diameter of 7 to 9 mm.

15. An open mold according to claim 11, wherein the height of the transition open cylindrical or frusto-conical cavity is equal to 0.01 to 0.2 mm.

16. An open mold according to claim 15, wherein the height of the transition open cylindrical or frusto-conical cavity is equal to 0.03 to 0.0 gmm.

17. An open mold according to claim 11, wherein the volume of the open concave cavity, or alternatively, the combined volume of the open concave cavity and the transition open cylindrical or frusto-conical cavity, is equal to 15 to 175 μ l.

18. An open mold according to claim 17, wherein the volume of the open concave cavity, or alternatively, the combined volume of the open concave cavity and the transition open cylindrical or frusto-conical cavity, is equal to 25 to 55 μ l.

19. An open mold according to claim 11, wherein it is formed of a polymeric plastic that is not wettable by said liquid polymer precursor or is only incompletely wettable by said liquid polymer precursor.

20. An open mold according to claim 19, wherein said polymeric plastic is a polyolefin.