Note: Descriptions are shown in the official language in which they were submitted.
V-17969/1+2/=/TIT 12
Ophthalmic lenses based on amorphous fluoropolymers
The invention relates to ophthalmic lenses, such as contact lenses and intraocular lenses,
which essentially consist of amorphous fluoropolymers, to processes for the production of
such lenses, to such processes, including subsequent surface treatrnents, and to the use of
corresponding amorphous fluoropolymers for the production of contact lenses and intra-
ocular lenses.
Amorphous fluoropolymers are further developments of polytetrafluoroethylene which has
already been known for some decades. Amorphous fluoropolymers are disclosed, for ex-
ample, in EP-A-073 087 or EP-A-l l l 343. According to EP-A-073 087, these are copoly-
mers which are obtained from tetrafluoroethylene and perfluoro-2,2-dimethyl-1,3-dioxole,
and possibly a third monomer, for example propylene, isobutylene or ethylene. Polytetra-
fluoroethylene compositions which are prepared, for example, using certain amounts of
the abovementioned dioxole or derivatives thereof are disc losed in EP-A- 111 343.
Since 1989, such amorphous fluoropolymers have also been commercially available.Thus, Dupont markets the products Teflon AF 1600 and 2400, in which "AF" means
"Amorphous Fluoropolymer". These products are copolymers of tetr~fluoroethylene and
perfluoro-2,2-dimethyl-1,3-dioxole.
According to EP-A-073 087, the amorphous copolymers disclosed therein are suitable for
uses such as windows for chemical reactions, specifically in processes in which hydrogen
fluoride is used or forms. The amorphous copolymers disclosed in EP-A-111 343 are
described as being useful in making molded parts, specifically in instances where smooth
surfaces are important, such as ball valve seats. The polymers Teflon AF 160Q and 2400 ;
marketed by Dupont are described in the product description accompanying them as being
suitable for coatings or coverings for optical devices, including those which are used
within wide temperature ranges and in a chemically aggressive environment. Elsewhere in
the advertising material it states that Teflon AF is an ideal candidate for optical devices
for medicine, military, aerospace and industry.
It has now been found that, surprisingly, ophthalmic lenses having exceptionally advanta-
geous properties can be produced from amorphous fluoropolymers. Contact lenses or
intraocular lenses according to the invention thus have a combination of high hardness and
oxygen perrneability. They moreover have such a high glass transition point that they can
be autoclaved. In addition, their crystallinity and refractive index are decidedly low. The
refractive index can be, for example, made close to the refractive index of the lacrimal
film, so that an optimum course of ray results. The refrac~ive index can be adjusted, for
example, by varying the nature and amount of comonomers used. According to the in-
vention, for example, toric contact lenses of low refractive index can thus also be pro-
duced. If intraocular lenses according to the invention are used, fewer complications in
respect of secondary cataract formation are expected in view of the material properties.
If materials having a refractive index of between 1.47 and 1.52 are used and a contact lens
geometry which is toric on the inside is used, an artificial residual astigmatism arises
between the lacrimal fluid and lens material because of the differences in refractive index,
and this then has to be corrected on the front curve of the lens with the aid of a toric
surface. The production and fitting of such lenses is very expensive.
On the other hand, if a lens material according to the invention having a refractive index
of between 1.31 and 1.33 is used to deal with relatively highly astigmatic corneas, there is
either no jump or only a very small jump in refractive index. Correction of the undesirable
artificial residual astigmatism is thus unnecessary. This makes the lenses and their fitting
considerably cheaper.
If materials of relatively low refractive index are used, there is usually a non-optimal
distribution of the overall thickness. In extreme cases, the relatively steep lenticular rise
leads to incompatibility. However, this effect can be avoided by using a corneoscleral
design. A corneoscleral design having diameters of between 11.5 and 13.5 mm not only
leads to a general improvement in compatibility because of the large diameter, but allows
a balanced division of the lens between the corneoscleral haptic and the optically active
surface. The corneoscleral haptic can be designed perfectly here in respect of compability
without taking into consideration the optical requirements. The unfavourable distribution
of overall thickness which occurs al: the low refractive index has an effect only in the
optically active part and in no way affects the compatibility.
Another great advanlage of the material according to the invention lies in the high oxygen
P r
3 ~
permeability, which means that it is particularly predestined for corneoscleral design. In-
corporating measures for adequate rinsing behind the contact lens (turbo effect, microla-
crimation and the like), it is possible to use the material in combination with the corneo-
scleral design under particularly adverse circumstances, and moreover the material is
suitable for wearing for several days.
The ophthalmic lenses according to the invention therefore combine a range of favourable
parameters such as have not been described for contact lenses or intraocular lenses to date.
The invention therefore relates to ophthalmic lenses consisting essentially of an
amorphous copolymer which comprises units of the formula I
--fF fF
O O
(C~a ~CF2)b (I)
R/ \R
and units of the formula II
-CF2-CF2- (II)
in which a and b independently of one another are zero, one or two, and in which R1 and
R2 independently of one another are perfluorinated lower alkyl.
Perfluorinated lower alkyl contains up to 7 carbon atoms, in particular up to 4 carbon
atoms, and is, for example, perfluorinated methyl, ethyl, propyl, iso-propyl, butyl, iso-
butyl or tert-butyl, preferably trifluoromethyl. -
The units of the formula I and of the formula II can be present as blocks or can alternate
randomly. The content of units of the forrnula I is preferably at least 10 mol per cent and is
particularly 10 to 80 mol %.
The sum of the indices a and b in a unit of the formula I is preferably not greater than two.
The indices a and b are particularly preferably zero. In a specific embodiment, a and b are
- 4 -
each zero and Rl and R2 in each case are perfluorinated C~-C4aLkyl, in particular tri-
fluoromethyl. According to this embodiment, further comonomers can be dispensed with
and the molar Tatio of units of the formula I to units of the forrnula II is in the range from
30:70 to 90:10, preferably in a range from 50:50 to 85: lS. Particularly preferred ratios of
units of the formula I to those of the forrnula II are about 50:50 and about ~0:20 ("about"
in this connection is to be understood as meaning a deviation of not more than +10 %).
In addition to the units of the formula I and II, the copolymer can comprise other units in
amounts of up to 40 mol % of the copolymer. These units can also be in the form of blocks
or can alternate randomly with one another or with units of the formula I and II. Suitable
units here are those of the formula III
-CF-CF2-
1R3 (III)
in which R3 is a perfluorinated alkyl radical of the formula CnF2n+l, in which n is 1 to 4, or
in which R3 is a perfluorinated cycloalkyl radical of the formula CmF2m " in which m is 5
to 8, and/or those of the formula IV
-CX-CX -
I I (IV)
R4 RS
in which X and X' independently of one another are hydrogen or fluorine and R4 and Rs
independently of one another are hydrogen, fluorine, lower alkyl or perfluorinated lower
alkyl, excluding those units of the forrnula IV in which X, X', R4 and R5 are fluorine.
A perfluorinated alkyl radical of the forrnula CnF2n+l is, for example, perfluoromethyl,
-ethyl or -propyl. A perfluorinated cycloalkyl radical of the formula CmF2m, is, for
example, perfluorocyclohexyl or -cyclopentyl. Perfluorinated lower alkyl R4 or R5 is as
defined above for Rl/R2. Lower alkyl R4 or Rs has up to 7, preferably up to 4, carbon
atoms and is, in particular, methyl, ethyl, propyl or butyl.
The units of the formula IV comprise perfluorinated, partly fluorinated and fluorine-free
units. Perfluorinated and fluorine-free units of the formula IV are preferred. The former
are those, for example, in which X, X' and Rs are fluorine and R4 is perfluorinated lower
S
alkyl. The latter are, for example, those in which X, X' and Rs are hydrogen and R4 is
lower alkyl. Partly fluorinated units of the forrnula IV are, for example, those in which X,
X' and Rs are hydrogen and R4 is perfluorinated lower aLlcyl.
Units of the formula I and II together with units of the formula III or together with units of
the formula IV, for example, can occur in the copolymer of which the ophthalmic lenses
according to the invention consist. Combinations of units of the formula I and II with units
of the formulae III and IV are also possible.
The total amount of units of the forrnula III and IV, where these are present, is preferably
up to 30 mol % of the copolymer, and particularly preferably up to 20 mol % of the copo-
lymer. An embodiment of Ihe invention which is likewise preferred comprises, however,
ophthalmic lenses of copolymers which consist to the extent of at least 90 mol %, more
appropriately to the extent of at least 95 mol %, and particularly preferably exclusively, of
units of the formula I and II. Ophthalmic lenses, specif1cally contact lenses, of the com-
mercially available materials Teflon AF 1600 and Teflon A~ 2400 or mixtures thereof are
most preferred. According to the knowledge of the inventors, these materials are copoly-
mers such as are used according to claim 4, containing ~0 mol % and 80-90 mol % respec-
tively of units of the fonnula I.
The monomers which are required for the preparation of the copolymers are known or can
be prepared in a manner wbich is known per se. For example, monomers which provide
units of the formula I in the copolymer are described in US Patent 3 978 030. The mono-
mers which provide units of the formula II or IV in the copolymer are all commercially
obtainable. The monomers which provide units of the formula III in the copolymer are
described in standard works, cf., for example, Houben-Weyl, supplement E~0.
The preparation of amorphous copolymers which are used for the preparation of the
contact lenses according to the invention is described, for example, in EP-A-073 087 and
EP-A-111 343.
In view of the fact that the copolymers used according to the invention can be processed as
thermoplastics, there is an abundance of possibilities of producing contact lenses from
them. The amorphous copolymers in the form of, for example, granules, powders or films
can in each case be used here as starting materials.
- 6 -
The lenses according to the invention can thus be produced by processes which are known
per se, such as static mould casting, spin casting, pressing, deep-drawing, thermoforming,
lathe cutting or laser machining.
. .
These process steps are known per se and therefore do not require more detailed explana-
tion for the expert. However, liquid monomers or monomer mixtures or solutions of solid
monomers which polymerise only in the course of the production of the lens or blank, are
usually used as starting materials for the production of contact lenses. The peculiarity of
the preparation processes according to the invention is that finished copolymers which are
thermoplastic are used as the starting materials. These materials therefore also allow
routes to be followed which are not usually taken for the production of contact lenses,
alongside the classical contact lens production processes, such as lathe cutting of a button,
spin casting or static mould casting in individual moulds, which, in some cases in
modirled form, can also be used with the present invention.
Static mould casting can be carried out, for example, by injection moulding. For this, the
amorphous copolymer is melted at temperatures of 160-240C, preferably 210-220C, and
is injected into the mould by means of an injection moulding machine. If moulds with a
base curve and front curve are used, contact lenses can be produced directly. It is further-
more possible to produce contact lenses by casting, by in~oducing a solution of the amor-
phous copolymer in an organic solvent into a mould with a concave curve and convex
curve, after which the solvent is allowed to evaporate. Suitable solvents in this and the fol-
lowing processes are, for example, perfluorinated ethers or perfluorinated hydrocarbons.
Spin casting can also be used according to the invention, by introducing a solution of the
amorphous copolymer into a mould for spin casting, after which the mould is rotated.
During this operation, the solvent evaporates. The finished contact lens, the dimensions of
which can be controlled by the dimensions of the mould, the speed of rotation and the
viscosity of the solution introduced, remains in the mould.
Pressing is carried out according to the invention, for example, by melting the amorphous
copolymer and pressing it in a mould or by compression moulding a film of the
amorphous copolymer. A film of the amorphous copolymer can be produced in a manner
which is known per se, for example by extrusion, by blowing or by casting a solution of
the amorphous copolymer.
A contact lens can also be produced in a manner which is known per se by deep-drawing
or thermoforming from a film produced, for example, as men~ioned above.
Lathe cutting is also suitable as the last process step for the production of contact lenses
according to the invention. This always applies i~, for example, a blank obtainable by one
s)f the abovementioned processes requires further working. Lathe cutting is to be under-
stood as meaning conventional machining of e.g. contact lens buttons. Corresponding
blanks can be produced, for example, by injection moulding, extrusion of round rods and
division thereof, casting from a solution or casting of a melt. The term contact lens blank
in this connection includes buttons or semi-mould products, for example base curve
blanks. Typical blanks have thicknesses of 4 or 6 mm and diameters of 10 to 17, for
example 12 or 14 mm.
Laser machining can also be used according to the invention, blanks or contact lenses
produced by one of the other processes being used as the starting material where they still
require additional fineworking of their surface.
Intraocular lenses according to the invention can also be produced in a manner which is
known per se, for example by lathe cutling processes or by pressing from powder,granules or film. Different haptics can be employed for intraocular lenses according to the
invention. The haptic here can be intregrated into the mould shape, or subsequently shaped
or cut out by laser cutting. Yarious haptics are described, for example, by P. Fechner in
Intraokularlinsen, Grundlagen und Operationslehre (Intraocular Lenses, Principles and
Operating Techniques), Ferdinand Enke Verlag, Stuttgart 1980.
As already mentioned, the ophthalmic lenses according to the inven~ion have excellent
physical parameters, such as a high hardness and oxygen permeability. For example,
hardnesses of 60-70 N/mm2 and Dk values of 280-350 units have been measured. Corre-
spondingly high hardnesses are otherwise only obtained at the expense of the Dk values,
and vice versa. Thus, for example, conventional materials having a hardness of
60-70 N/mm2 have Dk values of less than 100, and materials having Dk values of 150
have a hardness of 40 or less. The abovementioned combination of such a high hardness
with such a high oxygen permeability is therefore an outstanding property of the contact
lenses and intraocular lenses according to the invention, which distinguishes them consid-
erably and unexpectedly from the prior art. On the other hand, the wetting angle is com-
p~ratively high, so that it is desirable for the surface of the ophthalmic lenses according to ~ -
- 8- ~, t;
the invention to be made more wettable, especially in the case of contact lenses.
This invention thus furthermore relates to a process for hydrophilising the ophthalmic
lenses obtainable by the abovementioned processes and to lenses treated in this way. The
hydrophilising can be carried out in a manner which is known per se. Suitable processes
are, for example, treatment in plasma with gases, graft polymerisation with hydrophilic
monomers, introduction of hydroxyl groups by modification of the units of the forrnula I
or oxidation of copolymer constituents.
The treatment of, for example, contact lenses with gases in plasma is already known per
se. Examples of gases which can be used are 2~ 3, N2, He, Ar, NH3 or lower alkanes
having, for example, up to ~ carbon atoms, such as CH4, by themselves, as a mixture or as
a mixture with water vapour. However, the ~eatment in plasma with gases in connection
with this invention is not limited to the use of substances which are gases under normal
conditions (temperature and pressure). Instead, the term "gases" in this connection also
includes, according to the invention, compounds which have such a high vapour pressure
that they can produce a low pressure plasma. Examples of such compounds are low
molecular weight alkanes, alkenes, alcohols, amines, aldehydes, carboxylic acids,
carboxylic acid derivatives, such as hydrophilic esters or arnides, and ethers, each of
which can be used by themselves, as a mixture with one another or, for example, as a
mixture with oxygen, air and/or water vapour. Low molecular weight in this connection
means, in particular, compounds having a molecular weight of up to 200, preferably up to
140, particularly preferably up to 88.
~raft polymerisation with hydrophilic monomers is also akeady known, for example in
accordance with EP-A-220 919. It can be carried out in plasma or in solution. Suitable
hydrophilic monomers are the hydrophilic vinyl monomers usually used for contact lenses,
for example methacrylic acid, hydroxyethyl methacrylate, vinylpyrrolidone, N-vinyl-
methylacetamide, dimethylacrylamide or homologues thereof. This hydrophilisationmeasure is preferably carried out in suitable solvents, such as hydrocarbons, for example
aromatic hydrocarbons, such as toluene or dimethylbenzene, or aliphatic hydrocarbons, for
example hexane, and in the presence of agents which form free radicals, for example per-
compounds, for example hydrogen peroxide or peracids.
The units of the formula I always present in the contact lenses or intraocular lenses which
have not undergone specif1c surface treatment can be converted, for example by acid
tr ~
hydrolysis or in a basic medium in the presence of a hydrogen Iransfer agent, into groups
of the formula V
-C~CF-
H 1H (V)
the presence of which likewise increases the hydrophilicity of the surface. Examples of
suitable reagents for this are alkali metals, such as sodium or potassium, preferably in
solvents which can transfer hydrogen, such as ethers, in particular cyclic ethers, for
example tetrahydrofuran, or in ammonia, or acids, such as inorganic or organic acids, for
example hydrochloric acid, sulfuric acid or trifluoroacetic acid. The ophthalmic lenses
according to the invention can also be treated oxidatively in solution using oxidising
agents, for example hydrogen peroxide or nitric acid.
The inventi~sn is illustrated below with the aid of examples, but these are not intended to
limit the invention in any way. Temperatures are stated in degrees Celsius.
A: E~roduction of blanks, semi-finished lenses, contact lenses and intraocular lenses
Example 1: Teflon AF 1600 or 2400 granules are melted in an injection moulding machine
at 210-220C in a suitable manner and injected into the mould. The injection mould i3
designed as a single- or multi-cavity mould. The follow-up pressure on the moulding
composition and the cooling of the injection moulding in the mould are adjusted so that a
substantially stress-free blank having a diameter of about 14 mm and a thickness of 6 mm
is obtained. Residual stresses can be eliminated by subsequent annealing of the blanks
under normal atmosphere or N2 or in vacuo at 110C-140C.
Alternatively, the polymer melted in an extruder is processed to round rods having a dia-
meter of about 14 mm. The rods are annealed as a whole or cut into buttons 6 mm thick
and annealed.
Example 2a: Granules are injected into an injection mould as described in Example 1. The
mould is provided with inserts which are convex in shape. The radii of the inserts corre-
spond to the base curves of the desired contact lenses (so-called base curve blanks). The
radii are spherical. However, the base curve blanks can also be aspherical in shape, in
c~
- lo-
particular elliptical. Alternatively, the inserts are provided with an incorporated lens
diameter and lens edge. The final contact lens is obtained from these blanks by lathe
cutting the front curve.
2b According to this embodiment, the inserts are concave in shape, so that after the
corresponding base curve has been machined by lathe cutting, a flat, collecting or
scattering lens is obtained. Here also, the final lens diameter and the lens edge are
alternatively incorporated.
Example 3: As in Example 1, granules are plasticised in a suitable manner and injected
into a contac~ lens mould. The mould is shaped so that it reproduces the desired base
curve, diopter, diarneter, bevel and edge of the lens. The base curve is spherical, aspherical
or, as a particular embodiment, elliptical, as required.
Example 4: Granules or powder of Teflon AF 1600 or 2400 or a mixture thereof in a
balanced amount are heated at 200-220C in a suitable pressing mould and compressed
under pressure. The material or contact lens is allowed to cool in the mould, while
maintaining the pressure. The mould used is shaped as a button mould, semi-mould(Example 2) or lens mould (Example 3). The amount of granules or powder weighed out
depends on the mould used, as follows:
- for a button: 0.5-1.5 g
- for a semi-rnould: 0.1-0.9 g
- for lenses: 15-100 mg.
Example 5: Granules or powder of Teflon AF 1600 or 2400 are or is plasticised in a suita-
ble plasticising unit and the material is pressed through a slit orifice. The resulting film
0.2-0.5 mm thick is formed or pressed directly or later by a forming process, thermo-
forming, deep-drawing or compression moulding in a contact lens mould to give a contact
lens or intraocular lens. Alternatively, corresponding films are produced by the blowing
process.
Example 6: About 8-10 % by weight of granules or powder of Teflon AF 1600 or 2400 are
dissolved in a perfluorinated solvent, for example Galden(~' (Montedison) or Fluorinert(g)
(3M), if necessary while heating. A film is produced from the solution by stripping off the
solvent by heating, a fan or a vacuum. This film is shaped to a contact lens in accordance
with one of the forming processes (see Example 5).
Example 7: A solution, obtained according to Example 6, of the copolymer is introduced
into a prefabricated mould. The solvent is evaporated off by heating or in vacuo. The
mould is constructed so that it reproduces the front face of the lens with its diopter,
diameter and lens-edge configuration. The base curve is subsequently shaped using a
corresponding punch with the radius incorporated.
Example ~: A solution obtained according to Example 6, is introduced into a prefabricated
mould which turnec1 about its own axis. The mould is constructed so that it reproduces the
front curve of the contact lens with its diopter, diameter and edge. The solvent is evapo-
rated by heating, during which the mould is simultaneously rotated. Various radii of the
base curve are obtained by adjusting the speed of rotation (so-called spincast process).
B: Examples for hydrophilising contact lenses or intraocular lenses
Example 9: Finished contact lenses according to one of the above examples are exposed to
a corona discharge under normal atmosphere to improve the wettability. The contact
lenses are then equilibrated with physiological saline solution. Thereafter, the surface can
be wetted homogeneously.
Example 10: Contact lenses according to the invention with an untreated surface are
exposed to a plasma discharge. This is generated in an atmosphere of 2 or O3. Water
vapour can also be ad~nixed to these gases. After a treatment time of 10 seconds to 15
minutes, the lenses have a wetting angle of <40 (without treatmçnt >100). The same
results are achieved starting from N2, He, Ar, NH3 or CH~, by themselves or as a mixture.
Example 11: Contact lenses according to the invention with an untreated surface are
activated by means of Ar plasma. A hydrophilic surface is produced by graft polymers
using hydrophilic monomers such as methacrylic acid, HEMA, methacrylamide, vinyl-
pyrrolidone or N-vinylmethylacetamide. The same results are achieved starting from a
plasma of N2 or 2-
Example 12: The surfaces of contact lenses or intraocular lenses according to the inven-
tion having an untreated surface are activated with H2O2, as a powerful agent which forms
free radicals, in a solution of hexane and subjected to graft polymerisation by adding
- 1 2 -
hydrophilic monomers, as in Example 11. After eguilibration with physiological saline
solution, the wetting of the surface is significantly improved.
Example 13: Contact lenses according to the invention having an untreated surface are
exposed to a solution of Na/NH3 or Na/tetrahydrofuran (Tetra Etch~, Gore) in a dipping
process. After treatment with acetone and then water, excess reagent is rinsed off and the
lenses are equilibrated with physiological saline solution. The treatment is carried out for
1-60 seconds at room temperature or at temperatures up to 100C.
