Gas permeable contact lens and method and materials for its manufacture

A polymer is prepared by forming a mixture of 3-methacryloxypropytris(trimethylsiloxy) silane, methacrylic acid, cyclohexylmethacrylate, 2-hydroxypropylmethacrylate, m,p-styrylethyltrimethoxysilane, methyl methacrylate and a cross linker. A polymerization initiator is added to the mixture, and UV or thermal energy is supplied so that the mixture polymerizes to form a polymer that is transparent, hard, machinable and oxygen permeable. The polymer is cut into lenses, and the lenses are treated with acetyl chloride or another suitable chemical so that their surfaces become hydrophilic. The result is oxygen-permeable, hydrophilic, daily and extended-wear, hard contact lenses.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to contact lenses and, more particularly, to a novel 
and highly-effective daily-wear and extended-wear contact lens and to a 
method and material for its manufacture. 
2. Description of the Prior Art 
There is a great need for a contact lens that can be worn safely, 
comfortably and continuously for an extended time, for example one or two 
months, and that is inexpensive enough to be discarded after that time. It 
is essential that such a lens be highly oxygen permeable, since the pupil 
of the eye has no blood circulation and extracts the oxygen needed by its 
cells directly from the atmosphere. Ideally, such a lens should be hard so 
that it can correct for astigmatism. In order to be comfortable for the 
wearer, however, the lens must also be hydrophilic; that is, the contact 
angle of an air-water interface with a surface of the lens must be small. 
In conventional practice, measures taken to increase oxygen permeability 
increase contact angle, so that the lens becomes uncomfortable, and 
measures taken to reduce contact angle reduce oxygen permeability, so that 
the lens cannot be worn continuously for an extended period. This 
trade-off has thus far defeated efforts to produce an extended-wear 
contact lens having all of the desired properties. 
OBJECTS AND SUMMARY OF THE INVENTION 
An object of the invention is to remedy the problems outlined above and in 
particular to provide a novel, oxygen-permeable, hydrophilic, 
extended-wear, hard contact lens and a method and easily-machinable 
inexpensive material for its manufacture. 
In accordance with one aspect of the invention, a method of making a 
plastic material for a contact lens comprises the steps of: 
forming a mixture comprising initiators and at least one polymerizable 
silicone monomer selected from the group consisting of 
##STR1## 
and mixtures thereof, where 
R.sub.1 is selected from the group consisting of 
##STR2## 
where n=1 to 6, and mixtures thereof, 
R.sub.2 is selected from the group consisting of an alkyl group having from 
1 to 8 carbon atoms, a saturated cyclic group and a benzene ring, and 
mixtures thereof, 
R.sub.3 is selected from the group consisting of 
##STR3## 
where n=1 to 6, and mixtures thereof, and 
R.sub.4 is selected from the group consisting of 
##STR4## 
where n=1 to 6, and mixtures thereof; and 
supplying energy to said mixture so that said mixture polymerizes to form a 
polymer that is transparent, hard, machinable and oxygen permeable. 
In accordance with a second aspect of the invention, a polymer for making a 
contact lens comprises 0% to 30% by weight of a hydrophilic agent, 0.1% to 
5% by weight of a cross linker, 0.05% to 1.0% by weight of a 
polymerization initiator, and 2% to 94.85% by weight of at least one 
polymerizable silicone monomer selected from the group consisting of 
##STR5## 
and mixtures thereof, where 
R.sub.1 is selected from the group consisting of 
##STR6## 
when n=1 to 6, and mixtures thereof, 
R.sub.2 is selected from the group consisting of an alkyl group having from 
1 to 8 carbon atoms, a saturated cyclic group and a benzene ring, and 
mixtures thereof, 
R.sub.3 is selected from the group consisting of 
##STR7## 
where n=1 to 6, and mixtures thereof, and 
R.sub.4 is selected from the group consisting of 
##STR8## 
where n=1 to 6, and mixtures thereof, 
the polymer being transparent, hard, machinable and oxygen permeable. 
In accordance with a third aspect of the invention, a contact lens is made 
of a polymer comprising 0% to 30% by weight of a hydrophilic agent, 0.1% 
to 5% by weight of a cross linker, 0.05% to 1.0% by weight of a 
polymerization initiator, and 2% to 94.5% by weight of a polymerizable 
silicone monomer selected from the group consisting of 
##STR9## 
and mixtures thereof, where 
R.sub.1 is selected from the group consisting of 
##STR10## 
when n=1 to 6, and mixtures thereof, 
R.sub.2 is selected from the group consisting of an alkyl group having from 
1 to 8 carbon atoms, a saturated cyclic group and a benzene ring, and 
mixtures thereof, 
R.sub.3 is selected from the group consisting of 
##STR11## 
where n=1 to 6, and mixtures thereof, and 
R.sub.4 is selected from the group consisting of 
##STR12## 
where n=1 to 6, and mixtures thereof, 
the lens being transparent, hard, machinable and oxygen permeable.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIGS. 1 and 2 show a contact lens 10 made in accordance with the invention. 
The lens 10 comprises an inner surface 12 ("base curve") that makes 
contact with the eyeball of the wearer so that it covers at least the 
pupil and an outer surface 14 that is intermittently wiped or covered by 
the eyelid. The lens 10 is curved to conform substantially to the shape of 
the portion of the eyeball covered by the lens and may be thicker at the 
center than at the edges ("convex"), as shown, to improve vision at close 
distances or thicker at the edges than at the center ("concave") to 
improve vision at long distances. If the lens is hard and formed with 
spherical surfaces, it automatically corrects for astigmatism as well as 
nearsightedness or farsightedness to the extent that the astigmatism is 
due to nonspherical curvature of the front of the eyeball. 
FIG. 3 shows apparatus 16 for measuring the contact angle of an air-water 
interface with a surface of a contact lens. In this case, the lens 10 is 
submerged in water (or preferably normal saline) 18 contained in a vessel 
20, and an air bubble 22 is introduced by a syringe 24 provided with a 
long, curved needle 26 so that the air bubble 22 is trapped below the 
lower surface 14 of the lens. It is also possible to place a drop of water 
(or preferably normal saline) on a lens in air, and to measure the contact 
angle through the drop of water. The method illustrated is preferred, 
however, since it measures the contact angle of the lens when the lens is 
hydrated and therefore more nearly duplicates the conditions that prevail 
when the lens is in place in the eye. 
In either case, an air-water interface 28 forms a contact angle A (FIG. 4) 
with the lens surface. The contact angle A is measured through the water 
or normal saline 18 and is defined by tangents T1 and T2 to the air bubble 
22 and to the surface 14 of the lens, respectively. The tangents T1 and T2 
are taken at the intersection of the air bubble 22 and the surface 14 of 
the lens. If the angle A is large, for example 60.degree. or more, it 
indicates that the surface is relatively hydrophobic, like the waxed 
finish of a car on which raindrops form into beads. A contact lens having 
a hydrophobic surface is uncomfortable for the wearer. On the other hand, 
if the contact angle A is small, for example 25.degree. or less, it 
indicates that the surface is relatively hydrophilic. A contact lens 
having a hydrophilic surface is much more comfortable for the wearer. 
In accordance with the invention, a plastic material for making a contact 
lens is prepared by forming a mixture comprising 0% to 30% by weight of a 
hydrophilic agent, 0.1% to 5% by weight of a cross linker, 0.05% to 1.0% 
by weight of a polymerization initiator, and 2% to 94.85% by weight of at 
least one polymerizable silicone monomer selected from the group 
consisting of 
##STR13## 
and mixtures thereof, where 
R.sub.1 is selected from the group consisting of 
##STR14## 
when n=1 to 6, and mixtures thereof, 
R.sub.2 is selected from the group consisting of an alkyl group having from 
1 to 8 carbon atoms, a saturated cyclic group and a benzene ring, said 
mixtures thereof, 
R.sub.3 is selected from the group consisting of 
##STR15## 
where n=1 to 6, and mixtures thereof, and 
R.sub.4 is selected from the group consisting of 
##STR16## 
where n=1 to 6, and mixtures thereof; and 
supplying energy to the mixture so that the mixture polymerizes to form a 
polymer that is transparent, hard, machinable and oxygen permeable. 
Energy is supplied to the mixture so that the mixture polymerizes to form a 
polymer that is transparent, hard, machinable and oxygen permeable. The 
polymerization temperature is within a range of 30.degree. C. to 
70.degree. C. The time for polymerization to be completed using heat 
energy ranges from 48 hours (at 30.degree. C.) for 30 minutes (at 
70.degree. C.). Polymerization may be completed at room temperature in 30 
minutes to one hour using ultraviolet radiation. 
The polymerizable material is preferably m,p-styrylethyltrimethoxysilane or 
S1588, and the cross linker is preferably ethyleneglycoldimethacrylate or 
EGDMA. 
The polymerization initiator is selected from the group consisting 
essentially of 2,2'-azobis(2,4-dimethylvaleronitrile) or VAZ052, 
benzoinmethylether or BME, and sec-butylperoxydicarbonate or SBC. The 
first initiator may be used when polymerization is aided by ultraviolet or 
thermal radiation, the second when polymerization is aided by ultraviolet 
radiation, and the third when polymerization is aided by thermal 
radiation. The polymerization initiator is present in the mixture in an 
amount ranging from 0.05% to 0.5% by weight. 
Energy is supplied in the form of thermal energy or in the form of 
ultraviolet radiation, as may be appropriate in view of the initiator 
employed. 
Preferably the mixture comprising substantially 50% by weight of 
3-methacryloxypropytris(trimethylsiloxy)silane or OTC1, substantially 8% 
by weight of methacrylic acid or MA, substantially 7% by weight of 
cyclohexylmethacrylate or CHMA, substantially 5% by weight of 
2-hydroxypropylmethacrylate or 2-HPMA, substantially 15% by weight of 
m,p-styrylethyltrimethoxysilane or S1588, substantially 14% by weight of 
methyl methacrylate or MMA, and substantially 1% by weight of 
ethyleneglycoldimethacrylate or EGDMA. 
The method further comprises the steps of forming the polymer into a 
contact lens and treating a surface of the contact lens with a chemical to 
reduce the contact angle of an air-water interface with the surface of the 
lens. The chemical is preferably selected from the group consisting 
essentially of NaOH, AcCl, and H.sub.2 SO.sub.4. 
Thus the polymer for making the contact lens comprises the same 
constituents in the same proportions as the mixture described above. The 
resulting lens also comprises the same materials in the same proportions. 
Before the treatment to hydrophilize the surfaces of the lens, the polymer 
in one embodiment of the invention (employing S1588) may be represented as 
##STR17## 
where R is 
##STR18## 
Treatment with 5% by weight H.sub.2 SO.sub.4 in 95% by weight of H.sub.2 O 
for one hour yields a mixture of 
##STR19## 
on the surfaces of the contact lens and evolves CH.sub.4 as a gas. The 
resulting lens has a shore hardness (D scale) within the range of 80 to 
90. Oxygen permeability in ml cm/cm.sup.2 sec cmHg.times.10.sup.-10 is 
shown in the second two columns of Table I (normal eye temperature to 
about 35.degree. C.). 
TABLE I 
______________________________________ 
lens center 
thickness (mm) 25.degree. C. 
35.degree. C. 
______________________________________ 
.125 40.9 51.8 
.157 43.5 57.7 
.215 45.0 60.2 
.295 47.1 64.4 
______________________________________ 
Contact angle is shown in Table 2. 
TABLE II 
______________________________________ 
After surface treat- 
After surface 
Before In ment with 2N NaOH 
treatment with 
surface 
saline for 20 minutes and 
25% AcCl for 
treatment 
for 48 hrs 
saline for 48 hrs 
20 minutes 
______________________________________ 
31.degree.-60.degree. 
11.degree.-65.degree. 
12.degree.-25.degree. 
15.degree. 
______________________________________ 
Light transmission is 97+%, specific gravity is about 1.09, and refractive 
index is about 1.47. 
Before the treatment to hydrophilize the surfaces of the lens, the polymer 
in another embodiment of the invention (employing T3633) may be 
represented as 
##STR20## 
where R' is 
##STR21## 
Treatment with 5% by weight H.sub.2 SO.sub.4 in 95% by weight of H.sub.2 O 
for one hour yields: 
##STR22## 
on the surfaces of the contact lens and evolves CH.sub.4 as a gas. The 
resulting lens has a shore hardness (D scale) within the range of 80 to 
90. Oxygen permeability and contact angle are close to the values set 
forth in Tables I and II for lenses made from a polymer employing S1588. 
Light transmission is 97+%, specific gravity about 1.09, and refractive 
index is about 1.47. The material is however more brittle than that made 
with S1588. 
EXAMPLE I 
The following are mixed at 70.degree. C. in a 100 ml beaker: 
______________________________________ 
3-methacyloxypropytris(trimethylsiloxy) 
5.0 grams 
silane or OTCl 
methacrylic acid or MA .8 grams 
cyclohexylmethacrylate or CHMA 
.7 grams 
2-hydroxypropylmethacrylate or 2-HPMA 
.5 grams 
m,p-styrylethyltrimethoxysilane or S1588 
1.5 grams 
methyl methacrylate or MMA 
1.4 grams 
ethyleneglycoldimethacrylate or EGDMA 
.1 grams 
______________________________________ 
The ethyleneglycoldimethacrylate or EGDMA serves as a cross linker. As an 
initiator 0.02 grams of 2,2'-azobis(2,4-dimethylvaleronitrile) or VAZ052 
is added to the mixture, and the mixture while at room temperature is 
subjected to ultraviolet radiation from a 20-watt ultraviolet lamp placed 
at a distance of approximately 20 cm from the mixture. The mixture 
polymerizes within 30 minutes to form a hard polymer. The polymer is 
easily cut to the shape of a contact lens having a center thickness of 0.2 
mm or less and polished. The lens is highly transparent and has uniform 
optical properties. It has an oxygen permeability of 58.6.times.10.sup.-10 
ml cm/cm.sup.2 sec cmHg at 35.degree. C. The lens is subjected to a 
surface treatment with 25% AcCl for 20 minutes and is found to have a 
contact angle of 8.degree.. 
The following examples are similar to Example I but illustrate variations 
of the materials and the quantities thereof employed. 
EXAMPLE II 
______________________________________ 
OTCl 32 grams 
MA 4 grams 
2-HPMA 2.6 grams 
T-3633 10 grams 
EDGMA 1.42 grams 
azobisisobutyronitrile or AIBN 
0.3 grams 
______________________________________ 
EXAMPLE III 
______________________________________ 
OTCl 3.08 grams 
MA 0.39 grams 
CHMA 0.34 grams 
2-HPMA 0.24 grams 
S-1588 1.00 grams 
AIBN 0.03 grams 
______________________________________ 
EXAMPLE IV 
______________________________________ 
OTCl 2.9 grams 
MA 0.4 grams 
CHMA 0.35 grams 
2-HPMA 0.25 grams 
S-1588 0.53 grams 
T-3633 0.51 grams 
EGDMA 0.10 grams 
AIBN 0.03 grams 
______________________________________ 
EXAMPLE V 
______________________________________ 
OTCl 2.9 grams 
MA 0.4 grams 
CHMA 0.35 grams 
2-HPMA 0.25 grams 
S-1588 0.25 grams 
T-3633 0.75 grams 
EGDMA 0.10 grams 
AIBN 0.03 grams 
______________________________________ 
EXAMPLE VI 
______________________________________ 
OTCl 2.5 grams 
MA 0.4 grams 
2-HPMA 0.25 grams 
MMA 0.75 grams 
S-1588 0.26 grams 
T-3633 0.75 grams 
EGDMA 0.10 grams 
AIBN 0.03 grams 
______________________________________ 
CL EXAMPLE VII 
______________________________________ 
OTCl 2.5 grams 
MA 0.39 grams 
CHMA 0.35 grams 
2-HPMA 0.25 grams 
MMA 0.70 grams 
S-1588 0.75 grams 
EGDMA 0.05 grams 
AIBN 0.03 grams 
______________________________________ 
EXAMPLE VIII 
______________________________________ 
OTC1 2.50 grams 
MA 0.40 grams 
CHMA 0.35 grams 
Isoborylmethacrylate 
0.70 grams 
S-1588 0.75 grams 
EGDMA 0.05 grams 
2-HPMA 0.25 grams 
AIBN 0.03 grams 
______________________________________ 
Thus there is provided in accordance with the invention a novel, 
disposable, extended-wear, oxygen-permeable, hydrophilic, inexpensive, 
hard contact lens and a method and easily machinable material for its 
manufacture. Many modifications of the preferred embodiments of the 
invention disclosed above will readily occur to those skilled in the art 
upon consideration of this disclosure. For example, initiators and 
surface-treatment chemicals other than the ones disclosed may be employed, 
the contact lens may be tinted or clear, the temperatures and times of 
polymerization may vary, etc. Accordingly, the invention is not limited 
except by the appended claims.