Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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rrhe pre~ent application is divided out of our Canadian ~a~ent Appli-
r,~ cation Serial No. 240,087, filed November 2Q, 1975 and relates to a mold fort
casting substantially strain-free, dimensionally stable ~ wherein
the cas.ting process includes a polymerization which is inhibited by the pres-
~D~ D~
ence of oxygen. The ~ol~^ric-rod may be, for example, of a material which is
suitable for use in manufacture of contact lenses or shaped eye bandages such
as those which are the subject of Application Serial No. 240,087.
Contact lens compositions prepared from polymeric materials are
known:
lQ United States Patent No. 3,220,960 discloses hydrophilic copolymers
of a monoester of acrylic or methacrylic acid with a diester of acrylic or
methacrylic acid having desirable optical and physiological properties. - ~
United States Patent Nos. 3,408,429 and 3,496,524 disclose various aspects of ~ ~ -
contrifugal casting and manufacturing soft contact lenses using the hydrophilic
copolymers described in United States Patent No. 3,220,960.
United States Patent No. 3,700,761 discloses compositions comprising ~-
of HEMA (hydroxy-ethyl methacrylate) or HPMA (hydroxy-propyl methacrylate)
with PVP (pol~-N-vinyl pyrrolidone) in proportions of 20 - 45~, with up to 1% -MA (methacrylicacid) and about 0.2% EDMA (eth~lene glycol dimethacrylate).
A t~o stage polymerization process, followed by radiation curing, cutting and
hydration provides the finished contact lens.
United States Patents Nos.3,8169571, 3,822,196, and 3,82~,329 disclose
various aspects of the fabrication procedures generally described in aforemen-
tioned Patent No. 3,700,761.
United States Patent No. 3,8Q7,398 discloses improvements in the ~ -
United 5tates Patent No. 3,70Q,761 b~ careful regulation of ingredient con-
centrations and the addltion o$ certain polymerization inhibitors to stabili7e
the HEMA. rn addition, the polymeric composition is cast in a curved break
away mold which eliminatesthe need for grinding the cast surface of the lens.
3a It its overall aspect, Application Serial No. 2~0,087 deals with a -
dimensionall~ stable composition suitable for use in preparing a corrective ~ ;
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hydrated lens or an eye bandage. The composition is obtained by utilizing
from 0 to 4 ppm of HQ (hydroquinone) polymerization inhibitor and from 50 to
250 ppm of ME~IQ ~methyl ether of hydroquinone) polymerization inhibitor,
based on the amount of HEMA monomer, in the polymerization mix; initiating the
polymerization with a low temperature, free radical initiator; de-gassing the
polymerization mix prior to polymerization to remove substantially all oxygen;
and conducting the initial polymerization reaction from 23C to 30 C for 16 to
36 hours during which time the reaction exotherm is carefully controlled. A
closed castiny mold, lined with a polyester film material, is utilized for -
polymerizing and shaping the composition. The polymeric composition obtained ;
may be cut, machined and polished to obtain a contact lens composition which
is then hydrated in a buffered saline solution maintained at a pH of 7.0 to
7~
In a more specific aspect, Application Serial No. 240~087 provides a
composition which can be subjected to cutting and thereafter hydrated in a
buffered saline solution to provide a dimensionally stable contact lens or
shaped eye bandage having from about ~5% to about 65~ water after hydration,
said composition in dry form consisting essentially of polymerized random
graft copolymers containing from about 67~2~ to about 79~3% hydroxyethyl
methacrylate (HEMA); from about 14.25~ to about 32.4% poly-N-vinyl pyrroli-
done ~PVP); from about 0.1% to about 4. M ~ ethylene glycol dimethacrylate
~EDM~; Prom about 0.1% to about 2n5% methacrylic acid (MA); from about 0.1%
to about 5.0~ water; Prom about 0 to about 4.0 ppm, based on the weight of
HEMA monomer, of hydroquinone (HQ) inhib`itor; and Prom about 50 to 250 ppm, ~ -
based on the weight of HEM~ monomer, of the methylether of hydroquinone (MEHQ)
inhlbi~or, said composition having been polymerized in a three stage polymer-
ization process comprising:
a. a Pirst stage, using only a low temperature polymerization inhi-
bitor, with substantially all the o~ygen having been removed Prom the poly~
merization mix prior to and during the polymerization reaction; the initial
polymerization reaction being conducted at from about 23 to about 30C.~ for
from about 16 to about 36 hours, with the heat of the reaction continuously
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absorbed to control the reaction exothermi followed by
b. a secon~ stage, wherein ~he product of (a) i~ heated to a ~ ~
temperature of from about 40 to about 80C. in the absence of any additional ~ ~ .
polymerization initiator, without control of the reaction exotherm, for from
2 to 6 hours; followed by
c. a third stage polymerization, wherein the product of (b) is
heated to a temperature of from about 105 to about 125C., in the absence of
any additional polymerization initiator, for from 24 to 36 hours.
In another aspect, Application Serial No. 240,087 provides a pro- .
cess for obtaining a dimensionally-stahle, uniform composition for a contact
lens or a shaped eye bandage comprising: -
1. mixing a homogeneous blend of from about 67.2 to about 79.3
hydroxyethyl methacrylate; from about 14.25 to about 32.4~ poly-N-vinyl pyrrol-
idone, from about 0.1 to about 4.04% ethylene glycol dimethacrylate; from
about 0.1 to about 2.5% methacrylic acid; from about 0.1 to about 5.0% water;
from about 0 to 4 ppm, based on the weight of hydroxyethyl methacrylate mono-
mer, of hydroquinone inhibitor; from about 50 to 250 ppm, based on the weight ;
of hydroxyethyl methacrylate monomer, of the methyl ether of hydroquinone
inhibitor; and ~rom about 0.005 to about 0.20~ of a low temperature free radi-
cal polymerization initiator operable between temperatures of from about 23
to about 80 C;
2. de-gassing the polymerization mix to remove substantially all
oxygen and conducting the ~irst and second stages of the polymerization in an :
inert atmosphere;
3. in the first stage, heating the polynerization mix to from about ;~
23 to about 30 C., for from about 16 hours ~o about 36 hours with the heat ~:
of the reaction continuously absorbed to control the reaction exotherm; :
4. in the ~econd staqe, heating the partially polymerized product
of (3) to from about 40 to about 80 C., in the absenca of any additional
poly.merization initiator without controlling the reaction exotherm, for from
2 to 6 hours; and
5. in the third stage, heating the partially polymeri~ed product of
~3~
(4) to from about 105 to about 125C., in the absence of any additional poly-
merization initiator for from 24 to 36 hours.
A preferred embodiment of this process comprises: .
A. Lining an open-enaed mold with a polyester film material and
closing one end of the mold with a cap plug;
B. Placing a homogenous blend of from about 67.2~ to about 79.3~ of ~ :~
HEMA; from about 14.25% to about 32.4~ PVP; from about 0.1% to about 4.04%
EDMA; From about 0.1% to about 2.5~ MA; from about 0.1% to 5.0% water, from
about 0 to ~ ppm, based on the weight of H~ monomer, of HQ inhibitor; from
about 50 to 250 ppm, based on the weight of HEMA monomer, of MEHQ inhibitor
and from 0.005~ to about 0.2~ of a low temperature free radical polymerization
initiator operable between temperatures of from about 23 to 80C. into the
polyester-lined mold of tA);
C. De-gassing the homogenous blend o (B) while in the m~ld to re-
move substantially all oxygen present;
D. Closing the mold of (C) with a cap plug to prevent contamination
with at~ospheric oxygen;
E. Subjecting the homogenous blend of (D) to an initial polymeri-
zation reaction at a temperature of from about 23C to about 30 C for from :
about 16 hours to about 36 hours in a medium capable of continuously absorb-
ing the heat of the reaction;
F. Removing the mold from the heat absorbing medium of tE) and heat-
ing to a te~erature to from about 40C to about 80C for from bout two hours
to about six hour~ to form a solid, self-supporting, partially polymerized
mass;
G. Re~oving the cap plugs from the mold of (F) and gently forcing :
the solid mass, encased in the polyester film, $rom the mold;
H. Heating the solid ma~s of (G) encased in the polyester film, to
a temperature from 110C to 115 C for from about 24 hours ~o about 36 hours
to substantially complete polymerization of the contact lens composition;
I. Removing ~he polyester film casing from the polymer1zed con-
tact lens composition of (H); and subjecting the~lens co~position to cutting,
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machining and polishing to form a corrective contact lens or a shaped ocular
implant; and
J. Hydrating the contact lens or shaped ocular implant of (I) in a ~ ~
buffered saline solution at a pE of from about 7.0 to about 7.1 until from : :
about 45% to about 65% water has been absorbed.
~ ccording to the present invention there is provided a mold for
casting and polymerizing a polymer pre-mix which polymerizes in the absence
of o~ygen and is inhibited from polymerizing in the presence of oxygen, to
obtain a substantially strain~free, di~ensionally-stable polymeric rod from
which soft contact lenses ox shaped eye bandages can be fabricated, which ~ ~:
mold comprises:
A. an oxygen-absorbent outer cylindrical tube, impermeable to
fluids and capable of withstanding temperatures of from abo.ut 40C. to about ~:
80C.;
B. an oxygen non-absorbent spiral coil of film inert to said poly-
mer and its pre-polymer mix lining the interior surface of said tube, said
film being capable of withstanding temperatures of from 40 C. to about 125 C.; i
~rl!.$ and film being spiralLy coiled and positioned within said cylindrical tube .
in a manner such that ~'polymer pre-mix leakage within the coiled portion ~-
of the film comes in contact with oxygen absorbed through said cylindrical
tube and remains in an unpolymerized state; and
C. a removable, non-oxygen absorbent fluid-tight closure for each
end of said tube, inert to said polymer and its pre-polymer mix and capable
of withs~anding temperatures of from abou~ 40C. to about 80C; whereby
polymerization of the polymer in said mold produces a substantially strain-
free, dimensionally-stable solid rod which is releasab}e with said coil `~
through an open end of the tube upon removal of said closures and easily
separable rom said coil due to the unpolymerized state of the polymer leakage
~ into said spiral coil.
The invention will be further illustrated with reference to the
accompanying drawings showiny one embodiment of a mold according to the in-
vention, in which: ~ ~
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Figure 1 is a side exploded view showing the mold parts;
Figure 2 is an end view of the tube portion of the mold with a
polyester liner positioned therein; ~ - -
Fig~e 3 is a perspective front view of the flat polyester sheet;
and
Figure 4 is a perspective front view showing the coiled polyester
sheet.
Referring to Figure 1, an oxygen absorbent tube 1 has an end plug
2 and a cap 3 as a convenient closure for one end of tube 1. A split ring 4
or similar type device is useful to provide a support for the mold durins
suspension in a temperature-controlled fluid bath (not shown). Figure 2 is
an end view of tube 1 having a polyester film coil S lining the interior
surface of tube 1. Figure 3 shows a sheet 6 of the polyester film which may
be coiled as shown in Figure 4 prior to insertion in tube 1. Mold materials,
which are critical to the practice of the present invention, include an
oxygen ab~orbent material for tube 1 and an oxygen non-absorbent polyester
film as the lining 5 for the tube 1. The oxygen absorbent properties of
polytetrafluoroethylene are well known and tubes of the type illustrated are
~, r~
commerically available made of ~ef~3n ~rademark of E.I. duPont de Nemours,
Wilmington, Delaware). A suitable oxygen non-absorbent material for the
lining is exemplified by polyester films, especially the polyethylene
~L~R
terephthalate films marketed commerically as ~yaar (a Tra~emark of E.I.
duPont de Nemours, Wilmington,~Delaware). After the mold is filled with the
prepolymer mix, ~he other end of tube 1 is closed with pl~g 7~ Preferably
plugs 2 and 7 are also made of an oxygen non-absorbent polyester material.
The mold of this invention is particularly suitable for polymeriz-
ing materials in the shape of a rod or the like ~hich is to be later machined
into articles such as contact lenses. Examples of materials for which the
mold is particularly suited for use include polymers and mixtures of polymers
30 of methyl methacrylate, hydroxyethylmethacrylate and polycarbonates such as
poly(diethylene glycol bis-allyl carbonate) or CR39 ~Trademark of PPG ~ ~ -
,. . .
In~ustries, Pittsburgh, Pa.). The mold of the present in~ention may be used
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for casting rods of any polymer of a pre-polymer whose poly~rization is in-
hibited by the presence of oxygen. One advantage of the mold of the present
invention is the ease of removing the polymer rod from the mold after poly- -
merization. Another advantage of the mold, when used according to the present
invention, is the strain-free, dimensionally-stable characteristics of the
polymer product. m ese characteristics are especially important if the
ultimate products are contact lenses. The use of the mold of the invention -
is further described with reference to the formation of a polymeric rod from
which can be formed a contact lens or shaped eye bandage in accordance with
the invention of our Application Serial No. 240,087.
It has now been fou~d that a stable contact lens composition, suit-
able for precision cutting and shaping, followed by hydration in a buffered
saline solution, can be obtained by carefully controlling the formulation
ingredients, the polymerization processes and the molding techniques. The
stable contact lens product obtained has been found to be predictable and
reproducible both in the wet and dry states. Additionally, the improved con-
tact lens composition remains stable indefinitely without change in critîcal
dimenqions .
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Specifically, it has been found that while a polymerization in-
hibitor is needed, the hydroquinone inhibitor adversely affects the HEMA
polymerization as well as the polyHEMA/PVP graft polymerization reaction.
Therefore, no more than 4 ppm, based on the amount of HEMA, of hydroquinone
should be present for optimum polymer formation. The methyl ether of
hydroquinone, which does not exhibit the disadvantages of hydroquinone,
has been found to be effective at levels of 50 to 250 ppm, based on the
amount of HEMA, for inhibiting polymerization prior to the addition of the
polymerization initiator.
Additionally, it has been found that only a low temperature free
radical polymerization initiator is necessary for complete polymerization.
Prior art processes required an additional medium temperature free radical
polymerization initiators. According to the teachings of this invention,
initiators such as acetyl peroxide, disecondary-butyl peroxydicarbona-te,
cyclohexanone peroxide and the like, which operate between 23 C to 80 C,
are suitable to initiate polymerization, and no additional initia-tors are
necessary. Among these, disecondary-butyl peroxydicarbonate, used at a level
of .02% by weight, based on the weight of the polymerization mix is pre-
ferred.
The following formulation is suitable for preparing the dimension-
ally stable contact lens composition of this invention:
Ingredients Amount
HEMA 67.2% to 79.3%
PVP 1ll.25% to 35%
MA 0.1% to 2.5%
EDMA 0.1% to 4.~4%
Initiator 0.005% to 0.2%
Water 0.1% to 5.0%
HQ 0 to 4.0 ppm (par-ts) of HEMA
MEHQ 50 to 250 ppm (par-ts) of HEMA
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A preferred formulationS corrected for impurities, for preparing
the improved contact lens composition of this invention contains:
Ingredients Amount
HEMA 75.7%
PVP 19 . 1~%
MA 1.2%
EDMA 0.54%
Initiator 0.02%
Water 3%
HQ less than 4 ppm (parts) HEMA
MEHQ 100-200 ppm (parts) HEMA
Water in -the above formulations is not added as such: it is in-
herently present in ingredients such as HEMA and PVP, together with moisture
absorbed from the atmosphere prior to and subsequent to mixing and fabricat-
ing operations.
The above formulation is polymerized according to the improved -~
process of this invention. Specifically, the formulation is de-gassed prior
to polymerization to remove substantially all oxygen. Vacuum de-gassing,
using known techniques, has been found effective when performed on the -
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polymerization mix in the casting mold, just prior to polymerization.
Preferably, the de-gassing operation is performed twice: once on the poly-
merization mix, after -the addition of the polymerization initiator and
again a~ter the polymerization mix has been poured into the casting mold.
After the second de~gassing, the mold is back-flushed with an inert gas such -~ .. . .
as dry nitrogen, and the casting mold is immediately closed to prevent fur- ;
ther contamination with atmospheric o~ygen. The presence of oxygen and the
hydroquinone polymerization inhibitor have been found to seriously inhibit
both the HEMA polymerization and the polyHEMA/PVP graft polymerization
,. .
reactions. There~ore, by removing substantially all oxygenS including ;
atmospheric oxygen, before and during polymerization, and by limiting the
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amount of hydroquinone to less than four parts per million, based on the
amount of HEMA, bulk polymerization of HEMA will take place at low tempera-
tures.
High exothermic activity during the low temperature polymeriza-
tion reac-tion has also been found to adversely affect the physical charac-
teristics and uniform properties of the polymer -formed. Thus, while the
polymerization reaction may be conducted at temperatures of from 23 C to
30 C, with adjustments in amounts of polymerization initiator, the -tempera-
ture selected is controlled so that the reaction exotherm does not vary more
than about 4 C, preferably 2C during the 16-36 hour low temperature poly-
merization period. This may be accomplished by placing the closed casting ~ :
mold containing the de-gassed polymerization mix in a medium which will con-
tinuously absorb the heat of the polymerization reaction. Preferably, this
low temperature polymerization reaction is conducted by placing the mold
in a constant temperature water bath maintained at 25 ~ 0.1C -for about
24 hours. The closed mold is positioned in the bath so as to prevent con-
tamination of the polymerization mix with water from the bath. Most of the
HEMA is polymerized during this stage.
~ext, the mold is removed from the heat absorbing medium and heated ~-
to a temperature of ~rom about 40C to about 80 C for from two to six
hours in order to complete polymerization of any remaining HEMA monomer. ;
Preferably, the closed mold is placed in an oven maintained at a tempera-
ture of about 70 C for approximately two hours. ~ -
The completion of the graft polymerization of the PVP and the XEMA
polymer is achiered by heating the polymerized HEMA and the PVP to a tem-
perature from about 105 to 125 C for from 24 to 36 hours. This reaction -
can be performed after the reactants have been remo~ed from the mold since
the polymerized HEMA is in the solid state. ~referably, as will be explained ;
below, the reactants, encased in a polyester film material, are heated in
an oven maintained at 110 C ~or 24 hours.
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Substantially all bulk and graft polymerization reactions are
completed after the a~ove-mentioned heat treatment. An additional polymeri-
zation initiator operable at medium to high temperatures is not required
for curing. This is particularly advantageous since the benzoyl peroxide
initiator used to complete HEMA polymerization in prior processes has been
found to react with hydroquinone present in the polymerization mix to form
benzoquinone, which exerts a much ~ore powerful inhibiting effect than HQ
on the polymerization reactions taking place. Using the improved formula-
tion and polymerization process oX this invention, no further initiator
or post-suring steps are necessary. A cured polymeric product having sub-
stantially uniform physical properties is obtained without irradiation or ;
treatment with hydrogen peroxide previously required to achieve complete
cure.
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~ he oxygen absorbent and non-absorbent properties of the mola and
lining are particularly critical to the practice of the invention. m ese pro-
perties enable one to conduct the polymerization in the mold and ~emove the
rod cast by polymerization therein without difficulty or damage to the rod or
to the mold. ~he oxygen absorbent property of the mold tube prevents polymer-
ization of the mix in contact therewith. m erefore, any prepolymer mix which
leaks between layers of the coil or around the ends of the coil and contacts
tube 1 does not harden and/or bond either the rod and/or the polyester lining
to tube 1. Upon completion of the casting step it is therefore easy to remove
the rod with the polyester film from the tube and subsequently unwind the coil
from around the rod. m e mold size and shape is not critical and may be varied
to accommodate available lens fabricating equipment. Lens "buttons" or "rods"
of polymerized lens stock from which the individual lens can be cut may be ob-
tained according to the molaing process of this invention. In a preferred em-
bodiment, tubular, polytetrafluoroethylene casting molds of from 330-380 mil-
limeters in length and having inside diameter of approximately 15.8 millime-
ters are used. This apen-ended rod-shaped mold is lined with the polyester
film material and closed with top and bottom cap plugs at various stages
d~lring the molding operation. For example, after the polyester lining is in
place, the bottom cap plug is affixed and the polymeri~ation mix is added to
the mold; the polymer~zation mix is de-gassed, the system is bac~flushed
with an inert gas, and the top cap plug is affixed immediately to pxevent con-
tamination with atmospheric o~ygen. The polymerization reaction is then con-
ducked as described above. Removal of the polymerized mass from the mold is
facilitated by the presence of the polyester film lining; the top and bottom
cap plugs are removed, and the polyester encased self-supporting polymerized
mass can be removed by exerting a small amount of pressure on either
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end of the polymerized mass within the mold. The mold may be re-used after
a relatively simple cleaning operation. The self-supported polymerized
mass within the polyester film lining is heated at 110 C as described above,
to complete the graft polymeriza-tion reaction. The polyester film is then
removed from the polymerized rod and discarded. The cured rod stock thus
obtained can be cut and machined easily on existing contac-t lens equipment.
Techniques for cutting, machining, and polishing the contact lens
composi-tion prepared as described above are known in the art and are gen-
erally described by Mullen in United States Pa-tent 2,330,837, Feinbloom in
United States Patent 3,227,507, O'Driscoll et al. in United States Patent
3,700,761 and by Gruzca in United States Patent 3,807,398.
Individual contact lens compositions which have been cut, machined
and polished are hydrated in a buf'fered saline solution according to the
process of this invention. It has been found that the pH of the hydration
operation is critical and must be conducted at a pH of from about 7.0 to
about 7.1. A physiological saline solution (o.O5% to 0.9% sodium chloride)
is buffered with an ophthamalogically acceptable buffer ~hich will not in-
terfere with the optical qualitles of` the lens, to maintain the pH of from ~ ;
about 7.0 to about 7.1. Suitably, a monobasic sodium phosphate/dibasic
20 sodium phosphate buf'fer system is used for this purpose.
Hydration is conducted in the above-described solution ~or a time
sufficient to remove water-soluble extractables from the lens co~position
and establish a constant set of hydration parameters. It has been found
that the extractable levels as low as f'rom 2% to 3% are obtained using the ~ ;
improved formulating, polymerizing and molding processes of this invention.
Thus, hydration time is greatly reduced. Significantly, it has been found
that by using a 0.9% saline solution, buffered to maintain a pH of from
about 7.0 to 7.1, the equilibration of the contact lens composition of this
invention is achieved in f'rom five to seven days. In order to insure com-
30 plete equilibration, the hydration process is preferably conducted for seven
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days. Equilibra-ting and hydrating processes used for prior art contact lens
compositions frequently required a thirty day treatment period and numerous `
processing steps. By reducing the extractable levels in the polymeric com-
position and using the one-step hydration process of this invention, an im-
proved hydrated contact lens composition is obtained in a much shorter peri- ~ ;
od of time.
The hydrated contact lens compositions of this invention are
... . . .
suitable for use in correcting near-sightedness, far-sightedness and minor
astigmatism. The contact lens composition of this invention may also be
adapted for use as an eye bandage for dispensing medication.
As described by O'Driscoll et al. in United States Patent
3,700,761 and by Gruzca in United States Patent 3,807,398, water soluble ~ -
medicaments can be added to the contact lens by dissolving the medicaments
in water and adding 5% of the aqueous solu-tion of the medicament to the HEMA
monomer prior to polymerization. Especially useful eye bandages are pre-
pared in -this manner. The additional water in the polymerization mix makes
the lens, after hydration, spongy, and the medicament present is released
,
with greater facility. Opthalmologically accep-table medicaments suitable
for this purpose are known and include corticosteroids, sulfonamides, dis-
infectants, antiseptics, penicillin, pilocarpine, belladonna, dibenzyline,hydergine, methacholine, carbachol, bethanechol and the like.
In preparing the contact lens composition of this invention for
use as eye bandages to release medicament, formulating, polymerizing, molding,
and hydrating procedures may be varied within the above-mentioned critical
. . . .
limits to accommodate properties of the medicament being used. For example,
heating temperature and times may be lowered to avoid drug decomposition. Ad-
itionally, drug dosages for the eye which require a great degree of precision
can be administered using the shaped eye bandage of -this invention. In such
instances, it may be preferable to set up a fountain solution of the
drug in saline and drop this solution onto the lens to deliver the
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dosage to the eye at a constant rate for a controlled time.
In all of the aforementioned descriptions of the contact lens com-
positions of this invention, the abbreviations used are defined as follows:
HEMA - Hydroxyethyl Methacrylate
PVP - Poly-N-Vinyl Pyrrolidone
EDMA - Ethylene Glycol Dimethacrylate
MA - Methacrylic Acid
ppm - parts per million
HQ - Hydroquinone
MEHQ - Methyl Ether of Hydroquinone
Thus, according to the teachings of this invention there is ob-
tained a dimensionally stable contact lens composition suitable for use in
preparing a corrective hydrated lens or an eye bandage having uniform phys-
ical properties in both the wet and dry states, together with the required
strength and toughness for such lens compositions. The improved contaet
lens eomposition of this invention is obtained by critically seleeting for-
mulation ingredients and earefully eontrolling polymerization, molding and
hydration proeesses.
In order to further illustrate this invention the following exam-
ples are provided:
EXAMPLE 1 ~-
Preparation of the Contaet Lens Composition
665 Grams of HEMA, 170 grams of PVP, 10.2 grams of MA, 4.76 grams
of EDMA, .001 grams o~ HQ, and .oo65 grams of MEHQ are plaeed in a glass
eontainer whieh is closed with a MELAR lined cap. The bottle is shaken for
10 to 15 seconds to break up the PVP and then placed on a laboratory rolling
mill ~or 1 1/2 to 2 hours to complete solvation of the PVP. The premix is
removed from the glass container and pressure filtered through a Seitz or
pall filtering apparatus with 7 to 30 micron filter paper. The filtered
premix is refrigerated at 0 to ~ C.
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0.17 Grams of disecondary-butyl peroxydicarbonate is added to the
cold premix and the initiator-containing mix is then vigorously shaken for
ten seconds, after which it is placed on a rolling mill for 30 minutes. The
mix is then transferred in-to a suitable container and de-gassed for 10 to 15
minutes at 1-50 mm of reduced pressure. When releasing the vacuum, the
chamber is back-flushed with dry nitrogen.
A 5 mil MYLAR sheeting is cut into strips and rolled onto a steel
rod having a diameter of 12.7 mm and inserted into a TEFLON casting tube 330
millimeters long having an inside diameter of 15.8 millimeters and an out-
side diameter of 19.0 millimeters. The liner is wiped clean of gross par-
ticulate matter prior to insertion and the tube is blown out with dry nitro-
gen from both ends following insertion of the MYLAR liner. The bottom cap
plug, which has been soaked in acetone for 24 hours prior to use, is affixed
to the casting tube and the po-lymerization mix is poured into place. The
casting tube containing the polymerization mix is de-gassed in a vacuum
chamber for 20-40 minutes at 1-50 mm of reduced pressure. The system is
back-flushed with dr~ nitrogen as the vacuum is released. The casting tube
is removed from the vacuum chamber and the top cap plug is affixed tightly
immediately.
The closed casting tube is placed in a rack in a constant tempera-
ture water bath maintained at 25C + 0.1C for 20 hours, with the closed
casting tube positioned so as to prevent contamination of the polymerization
mix with water from the water baths. The casting tube is then transferred
to an air circulating oven set at 70 C + l C for two hours. The casting
tube is then taken out of the oven and the casting is taken out of the tube
by removing the cap plugs and then using a steel or aluminum poking rod.
The casting, encased in the MYLAR lining, slides easily out of the tube.
The liner is not removed and the encased casting is placed in an air cir-
culating oven, set at 110 C ~ 1 C for 24 hours. -
The ~YLAR liner is then removed, the cast rods are visually ` -
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~ 39~
inspec-ted and stored in sealed glass or MYLAR containers until needed. The
empty casting -tubes are cleaned by soaking in water, rinsing and allowing to
dry before reuse.
The hard polymeri~ed cast rods are subjec-ted to known machining,
cutting and polishing techniques as described in United States Patent Nos.
2,330,837, 3,227,507, 3,700,761, and 3,807,398, to form individual lens
compositions.
EXAMPLE II
Hydration of the Contact Lens Composition
A buffered physiological saline solution is prepared from 8.50
grams of reagent grade sodium chloride, .245~ grams mono-basic sodium phos- ;
phate, o.7006 grams dibasic sodium phosphate and distilled water, added to
1,000 ml. This buffered solution will maintain a pH of about 7.1. The in- ~ -
dividual contact lens compositions of Example I are hydrated in this solu-
tion at 22 C to 25C for seven days. Thereafter, the hydrated lens composi-
tions are stored indefinitely in saline solution.
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