Note: Descriptions are shown in the official language in which they were submitted.
4~3991
-- 1 --
This invention relates to a soft contact lens.
The soft contact lens of the invention is prepared from a
monomer mixture preferably containing trifluoro ethyl
methacrylate and/or hexafluoroisopropyl methacrylate and,
when used, is wette~l with tears or the iike only with
dif~iculty The invention makes it possible to provide a
soft contact lens having excellent mechanical strength and
elasticity which can retain its lens shape wi-th sufficient
stability even when processed into a thin lens.
In recent years, soft contact lenses (hereinafter
referred to as "soft lenses") have come to be widely used in
place of conventional hard contact lenses because of their
comfort of wearing. Most soft lenses are composed mainly
of 2-hydroxyethyl methacrylate (HEMA) or N-vinylpyrrolidone
(NVP), and have a water content within as a wide range as
from about 20 to 85~. Soft lenses vary in physical proper-
ties such as mechanical strength, refractive index, oxygen
permeability, specific gravity and the like depending on
the water content of the materials. In general, with in-
crease in the water content, the oxygen permeability in-
creases, but the mechanical strength decreases. Further the
refractive index and the specific gravity decrease and
approach the values for water.
Since the materials for soft lenses are high in
affinity for tears, the surfaces of the lenses are easily
wetted. Consequently, while soft lenses are used, resist-
ance to sof-t lenses on the epithelium of a cornea and on the
inner surface of an eyelid is reduced, so wearers of soft
lenses are relieved of discomfort due to the lenses as
toreign bodies. Further, sof-t lenses permit, to a certain
extent, -the supply of oxygen to a cornea epithelium through
-their own materials, and hence have a function of relieving
want of oxygen in a cornea to some degree.
Increase in the water content of soft lenses leads
to improvement in we-ttability and oxygen permeability
through the lenses, but results in lowering of the mechani-
cal strength of the materials, so that the lenses become ~7
~ZP41~9'9
-- 2
easier to break while handled. Ano-ther method for supplying
more oxygen to a co~nea, involves making the soft lenses
thinner. This method is advantageous in that wearers of
soft lenses are relieved of discomfort due to the lenses
acting as foreign bodies. However, according to this method,
the front side and the back side of the lense are difficult
to distinguish from each other when the lense is handled,
and -the lense tends to fold in two and the two halves ad-
here to each other when the lense is handled, so that the
lense can be very inconvenient when attached to an eye.
As a general problem in soft lenses, there is a
problem of contamination on the lenses. Contamination on
soft lenses is due to the adhesion of proteins, lipids,
mucoids and the like in tears; the denaturation, precipita-
tion and adhesion thereof by boiling; and the adhesion ofproteins, lipids and the like from fingers during handling
of the lenses. The lenses stained therewith show white
turbidity, color change to yellow and the like. Further,
when the precipitated and adhered matters form a layer, the
layer of these matters tends to crack, so that the surface
of the lense becomes uneven. Consequently, the surface of
the lense becomes water-repellent and is lowered in oxygen
permeability, so that the wearing comfort deteriorates.
Further, the formation of said layer facilitates propaga-
tion of fungi, bacteria and the like. When soft lenses areseriously deposited, the effect of improving visual acuity
by the lenses is greatly lessened and the discomfort due to
the lenses acting as foreign bodies becomes very serious.
The lenses sometimes become unusable. Further, the lenses
sometimes cause cornea disease of their wearers and hence
contamination is a serious problem in soft lenses. As one
mode of employment of a soft lens, it is sometimes attempt-
ed to provide, for continuous wear, a soft lens having a
high water content for a patient after a cataract operation.
3'~ llowever, in this case, since a material having a high water
content is used, tear composition is ap-t to penetrate into
-the material, and -the lens is liable to be contaminated
39~
because it cannot be washed everyday, which causes shorten-
ing of life of the lens.
When contamination of soft lenses is caused by a
tear composition, the contamination of the lenses varies
depending upon the di~ference in composition of tears among
wearers, but, in gelleral, there is strong suspicion of the
origin against proteins, particularly lysozyme present in
tears. Further, mucoids, lipids and the like appear to ad-
here complexly to the lysozymes.
As a treatment for contamination on soft lenses,
there are now used a washing treatment with a cleaner and a
treatment with an enzymatic agent, however, in a sense,
these are only passive countermeasures for removing deposits.
Further, these treatments sometimes cause deposits on the
lenses when the subsequent washing is insufficient.
In consideration of these facts, the present in-
ventors have attempted to impart deposit resistance to the
material itself for a sof-t lens without reducing its physi-
cal properties, and to developing a soft lens that retains
its lens shape sufficiently even when its thickness is small,
and is convenient for handling.
An object of this invention is to provide a soft
lens to which proteins, lipids, mucoids and the like from
tears and the like do not readily a~here.
Another object of this invention is to provide a
soft lens which retains its lens shape sufficiently even
when its thickness is small.
Accordingly, the present invention provides a soft
contact lens comprising a copolymer obtained by polymerizing
a composition comprising (~) at least 50% by weight of a-t
least one monomethacrylate of an alkylene glycol, (B) from 5
to 35% by weight of at least one fluorine-containing meth
acrylic ester wherein the ester moie-ty contains up to 4 car-
bon atoms, and (C) less than 40'~ by weight of one or more
compounds selected from the group consisting of an unsa-turat-
ed carboxylic aci-i having one or more carboxyl groups in the
molecule, a monomethacrylate of a polyhydric alcohol having
9~
-- 4
-three or more hydroxyl groups, and an alkyl me-thacrylate,
the percentages of (A), (B) and (C) being calculated on the
basis of the total weight of (A) + (B) -~ (C), and the sum of
the percentages of (A) + (B) + (C) being 100?6.
The fluorine-containing methacrylic ester is
advantageously a fluorine-containing alkyl ester wherein the
alkyl group contains at least one terminal -CF3 group
Trifluoroethyl methacryla-te (hereinafter abbreviated as
"TFEM" ), wherein the trifluoroethyl group has the formula
-CH2CF3, and/or hexafluoroisopropyl methacrylate (herein-
after abbreviated as "HFIPM" ), wherein the hexafluoroiso-
propyl group has the formula -CH (CF3) 2' are preferably used
as the fluorine-containing methacrylic ester, and the
invention is thus primarily discussed in terms of these com-
pounds. Other fluorine-containing methacrylic esters which
may be used include pentafluoro-n-propyl methacrylate,
wherein the pentafluoro propyl group has the formula
-CH2CF2CF3, and pentafluoro-n-butyl methacrylate, wherein
the pentafluoro-n-butyl group has the formula -CH2CH2CF2CF3.
The composition used in accordance with the in-
vention contains at least 50% by weight of component (A),
based on the total weight of (A) + (B) + (C1. The amount of
component (A) should not exceed 95% by weight. Componen-t
(C) must be present; that is the proportion of component
25 (C) cannot be zero.
The soft contact lens of the invention is prefer-
ably obtained by subjec-ting to casting polymerization by a
continuous and/or stepwise temperature raising method a com-
position as specified above, mechanically processing and
polishing the resulting polymer to give thereto a lens shape,
and then hydrating and swelling the shaped polymer. A
continuous and/or stepwise temperature raising method of
from 35 C to 110C is preferably used.
Advan-tageously the soft lens of this inven-tion is
35 obtained by subjecting to casting polymerization by a con-
tinuous or stepwise temperature-raising method from 35C to
110 C, a composition comprising 50 to 94?6 by weight of a
121489~
monomethacrylate of an alkylene glycol, 5 to 35~ by weight
of trifluoroethyl methacrylate "TFEM" and/or hexafluoroiso-
propyl methacrylate, and less than '~0~ by weight of one or
more compounds selected from the group consisting of an un-
saturated carboxylic acid having one or more carboxyl groupsin the molecule, a monomethacrylate of a polyhydric alcohol
having three or more hydroxyl groups, and an alkyl metha-
cryla-te; finishing the resulting polymer by mechanical pro-
cessing and polishing to give thereto a lens shape; and then
subjecting it to a hyclration and swelling treatment involv-
ing an alkali treatment.
Since at least one fluorine-containing monomer
such as TFEM or HFIPM is used in the soft lens of this in-
vention, foreign matter adheres less to the surface of the
soft lens, so that the soft lens is greatly reduced in sus-
ceptibility to color change to yellow and in white turbidity
as compared with conventional soft lenses. Further, the
lens can sufficiently retain its normal lens shape even when
processed so as to be thin, which is also a new property ob-
tained by the addition of at least one fluorine-containing
monomer such as TFEM and HFIPM.
The production of a soft lens by use of a fluorine-
containing acrylic or methacrylic ester has conventionally
been known (Louis Plambeck Jr.; Japanese Patent Appln. Kokai
(Laid-Open) 29,660/1978, U.S. Patent 4130706). However,
this process uses a fluorine-containing ester in which the
ester moiety is a straight chain having 5 or more carbon
atoms and uses no fluorine-containing ester in which the
ester moiety is short, for example with less than 5 carbon
atoms, such as TFEM and HFIPM used in this invention. It
has been confirmed that a hydroxyl group-containing monomer
and the fluorine-containing monomer used in the above-
mentioned patent are poor in miscibility with respect to
each other and ~ive only an opaque polymer by the usual bulk
polymerization. However, TFEM and HFIPM used in this inven-
tion can give a transparent polymer and lens without causing
white turbidity and opaqueness, by bulk polymerization with
L48~9~
the hydroxyl group containing monomer, which is a novel
finding by the presen-t inventors. Further, unlike this in-
vention, the above-mentioned patent does not aim at ob-
taining a deposit-resistan-t soft lens. When at least one
fluorine-containing monomer such as TEEM, HFIPM or the
like is used as a copolymer component as in this invention,
a soft lens good of shape stability, elasticity and mecha-
nical strength can be obtained even when the thickness of
-the lens is small. Therefore, there could be obtained an
ideal soft lens which advantageously supplies oxygen to the
cornea of a lenswearer and gives only slight discomfort due
to the lens acting as a foreign body.
lt has become clear that, as compared with conven-
tional fluorine-free soft lenses, the soft lens of this
invention gives rise to reduced deposits of proteins, lipids
and mucoids. In particular, deposit with protein was
measured by use of lysozyme labeled with 125I to show a
significant difference in adsorption of the lysozyme
between the soft lens of this invention containing at least
one fluorine-containing monomer and a fluorine-free soft
lens having the same water content as that of the soft lens
of this invention.
Further, even when the thickness of the lens of
this invention was adjusted so as to be about one-third of
the conventional thickness (about 0.05 mm in central thick-
ness), the lens retained its shape, the phenomenon of a
lens becoming folded into two and stuck was not observed,
and the lens could be handled without inconvenience. This
was an unexpected result, and was the result of -the dis-
covery of a novel effect brought about by the employment ofat least one fluorine-containing monomer.
The fluorine-containing monomer is used in an
amount of 5 to 35% by weight. TFEM and HFIPM can be used
alone or simultaneously. However, when the added amount
of the fluorine-containing monomer is less than 5% by weight,
the effect of the monomer on antideposit is insufficient,
and with increase of the added a~ount, the effect on an-ti-
~2~4~9~
-- 7deposit is heigh-tened, but the elasticity of the resulting
soft lens is reduced. When the added amount exceeds 35%
by weight, elasticity required of a soft lens becomes un-
obtainable. Preferably, an amount of from 10 to 20% by
5 weight is employed.
rlhe monomethacrylate of an alkylene glycol is, for
example, the monomethacrylate of ethylene glycol, propylene
glycol, die-thylene glycol, tetraethylene glycol or a poly-
ethylene glycol, and is the main constituent of the soft
lens of this invention. As the monomethacrylate, e-thylene
glycol monomethacrylate, i.e., 2-hydroxyethyl methacrylate
(2-HEMA) is preferably used. Simultaneous use of 2-
hydroxyethyl methacrylate and propylene glycol monomethacry-
late is also preferred.
Representative examples of the unsaturated car-
boxylic acids having one or more carboxyl groups in the
molecule include acrylic acid, metAacrylic acid, itaconic
acid and the like, and the unsaturated carboxylic acid is
a constituent for increasing the water content by a hydra-
20 tion and swelling treatment involving an alkali treatment
and for imparting elasticity required for a soft lens. As
the unsaturated carboxylic acid, methacrylic acid is par-
ticularly preferred.
As the monomethacrylate of a polyhydric alcohol
25 having three or more hydroxyl groups, glyceryl methacrylate
or monomethacrylate of pentaerythritol is preferably used,
and this constituent contributes to an increase of the
water content and to the elasticity.
The preferred alkyl methacrylate is the methyl
30 ethyl, n-propyl or n-butyl ester of methacrylic acid, and
is a constituent for improving the strength, processability
and shape stability of the resulting soft lens.
In addition to these constituents, there may be
used, as cross linking agents, polyfunctional monomers
35 such as ethylene glycol dimethacrylate, diethylene glycol
dimethacrylate, triethylene glycol dimethacrylate,
tetraethylene glycol dime-thacrylate, butylene glycol
dimethacrylate, neopentyl glycol dimethacrylate, propylene
:9l;2~41~9$i
glycol dimethacrylate, diethylene g]ycol bisallylcarbonate,
trimethylolpropane -trimethacrylate, bisphenol A dimethacry-
late, methylenebisacrylamide, and the like. N-vinylpyrroli-
done, acrylamide, methacrylamide or the like may be used as
a constituent for increasing the water content.
As the polymerization initiator, there may be
used any suitable radical-ge}lerating agents, for example,
benzoyl pero~ide, lauroyl peroxide, cumene hydroperoxide,
di-tert-bu-tyl peroxide, bis-4-tert-butylcyclohexyl peroxy-
dicarbonate, diisopropyl peroxydicarbonate azobisisobutyro-
nitrile, azobisisovaleronitrile and the like, and initiators
generating a radical at low temperatures are more preferable.
rn a preferred method for making the lenses of
this invention, the desired constituents are mixed and then
poured into a mold made of a metal, glass or plastics,
after which, while the resulting mixture is hermetically
sealed, polymerization is completed in an electric furnace
by a continuous-temperature-raising method of from 35 to
110 C. After completion of the polymerization, the result-
ing polymer is taken out of the mold and finished ~y usualmechanical processing and finishing to give thereto a lens
shape. In order to hydrate and swell the finished lens,
the lens is immersed in a physiological saline containing
sodium carbonate, sodium hydrogencarbonate, potassium hydro-
gencarbonate, and/or the like, at room temperature or with
hea-ting, and then immersed in a physiological salt solution
and allowed to stand at room temperature or heated while
the physiological salt solution is renewed several times, so
as to be hydrated and swollen.
The thus produced soft lens has the same optical
properties and elasticity as those of conventional soft
lenses, and enjoys such an effect from the content of at
least one fluorine-containing monomer that it is less
susceptible to adhesion of deposits due to proteins, lipids
and mucoids than conventional soft lenses. Fur-ther, a
soft lens retaining a lens shape sufficiently stably could
be ob-tained even when the thickness of the soft lens was
small.
This invention is further explained below in more
detall with reference to the Examples and Comparative
Examples, which are not by way of limitation but by way of
illustration. In the Examples and Comparative Examples,
parts are by weigh-t.
Example L
To a mixture of 89.7 parts of 2-hydroxyethyl metha-
crylate, 10 parts of TFEM and 0.3 part of methacrylic acid
was added 0.1 part of azobisisobutyronitrile as a polymeri-
zation initiator, and the resulting mixture was sufficientlystirred and mixed, poured into a mold made of plastics, and
then hermatically sealed up therein. The mixture was then
subjected to polymerization in a continuous-temperature-
raising furnace of from 35 to 110C, and the resulting
transparent polymer was processed by cutting and polishing
to give thereto a lens shape. The thus obtained lens was
treated in a physiological saline containing 1.2% of sodium
hydrogen-carbonate at 80 to 90C for 1 hour and then in a
physiological salt solution at 80 to 90 C for 1 hour,
whereby the lens was allowed to absorb water and swell and
at the same time, the unpolymerized monomer was eluted from
the lens. The thus obtained soft lens had a water content
of 35% and a tensile strength of about 850 g/mm2, was
comfortable to wear, and, as shown in Table 1, adsorbed only
very small amount of protein (lysozyme) as compared with a
conventional soft lens having the same water content, though
it was equal in optical properties to the conventional soft
lens. Eurther, the soft lens, even when its thickness was
made smaller, had the same shape stability as did those
having a conventional thickness.
Example 2
To a mixture of 84 parts of 2-hydroxyethyl metha-
crylate, 15 parts of TFEM and 1 part of methacrylic acid
was added 0.1 part of diisopropyl peroxydicarbonate, and the
same procedure as described in Example 1 was followed to
obtain a soft lens having a water content of 36%. As shown
in Table 1, this lens adsorbed only very small amount of the
121489g
-- 10 --
protein as compared with the conventional soft lens having
the same water content and containing no fluorine compound.
Example 3
To ~ mixture of 70 parts of 2-hydroxyethyl meth-
acrylate, 10 parts of TFEM and 20 parts of glyceryl meth-
acrylate was added 0.1 part of bis-4-tert-butyl-cyclohexyl
peroxydicarbonate, and polymerization and lens processing
were carried out in the same manner as in Example 1, after
which the thus obtained lens was treated in a physiological
salt solution at 80 to 90C for 2 hours to produce a soft
lens having a water content of 36%. This soft lens had
excellent resistance to deposit.
Examples 4 to 14
Soft lenses having various compositions and water
contents were produced by the same technique as in Examples
1 to 3. All the soft lenses were colorless and transparent,
had the same optical properties, mechanical processability
and strength as conventional soft lenses, and were less
susceptible to deposit with proteins. The soft lenses had
good shape stability even when they were thin.
Comparative Examples 1 to 4
By the same technique as in Examples 1 to 3, soft
lenses were produced from individual polymers having various
compositions containing no fluorine-containing monomer, and
were used as controls.
Each of the soft lenses obtained in the above
Examples and Comparative Examples was immersed in a solution
of egg white lysozyme labeled with radioactive iodine (125I)
(concentration 500 ~g/ml; pH 7.3; 0.05 M borate buffer), and
taken out of the solution after 2.5 hours, 24 hours, 3 days
and 10 days, and the lens surface was washed with flowing
water. Thereafter, the amount of egg white lysozyme adhered
to the lens was measured by a method by which y-rays were
detected by means of a well-type scintillation counter. As
shown in Tables 1 to 4, the amounts of lysozyme adhered to
the lenses of the comparative examples 1 to 4 containing no
fluorine-containing monomer as a copolymer component are
taken as 100%, and those in the examples are shown in com-
parison therewith.
The shape stability is expressed by ~ , o, ~ or
x (explai.ned below) based on the observation of the elasti-
city, ability to restore the original shape during handling,and shape stability during handling of a thin lens (central
thickness:0.05 mm). The tensile strength is expressed in
terms oE g/rnm .
~ : Greatly excellent shape stability and
elasticity
o : Excellent shape stability and elasticity
L~ : A little :inferior shape stability and
elasticitv
x : Inferior shape stability and elasticity
~z~
-- 12 --
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- 16 -
When trifluoroethyl methacrylate and/or hexafluo-
roisopropyl methacrylate, which are fluorine-coII-taining
monomers, are included in a monomer mixture for producing
a soft contact l.ens, -the resultin~ soft contact ]ens has
the same optical properties and elasticity as conventional
soft contact lenses, and is very superior -to the convention-
al ones in resistance to deposit and in shape stability.
