Note: Descriptions are shown in the official language in which they were submitted.
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P~TENT
MOLD FOR AND METHOD OF MA~CING CONTACT
. AND ~NT_AOCULAR ~ENSES
BACKGROUND
1. Field of Invention
This invention relates to a means for lathe euttiny of contaet
and intraocular lens blanks by use of a new contact lens molcl.
2. Description of the Prior Art
US 4,188,353 granted February 12, 1980 to Charles W. Neefe
discloses a method of making plastie aspherie lenses by easting a
liquid monomer in a container, polymerizing the monomer to form a
solid having an aspherie optical surfaee formed within the
container and cutting a second optical surface on the solid lens
material with the eontainer supporting the lens material during
the cutting and polishing operation. The aspheric surface of the
container is formed by elamping the container in a jig and
applying pressure until the desired aspheric eurve is achieved.
US ~,229,390 granted Oetober 21, 1980 to Charles W. NeeEe
discloses the use of plastic molcls for molding contact lens blanks.
The molds also serve as the holding block to ~acilitate cutting to
the required lens thickness. Ilowever, measurin~ beEore and after
the cutting operation is required to determine the thickness oE the
lens bein~3 cut.
US ~,239,712 grantecl Deeember 16, 1980 to Charles W. Neefe
discloses a method for preparing contact lenses with bifocal
correction in the front (anterior) surface of the lens. The
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lenses are prepared frorn blanks cast in individual molcls. The
molds serve as the lathe arbor during the cutting process. Again
a series of thickness measurements are required.
In the general practice of the art, the mol~ containing the
cast lens blank is mounted into a lathe by the use of a collet.
The use of a collet necessitates several measurements in order to
insure obtaining a contact lens of the desired thickness. The
collet also subjects the mold to stress which in turn results in
poor optical quality due to slippage and lack of alignment
necessary for preparation of toric and bifocal types of contact
lenses.
SUMM~RY OF TH E I NVENT I ON
In accordance with this invention there is provided a mold
~or casting contact and intraocular lens blanks comprisiny a hollow
hemispherical base having attached to the apex (or the axis of the
hèmisphere perpendicular to the open edge of the interior hollow of
said hemisphere) thereof a cup-like molding cavity with the
surface in the bottom thereof having a curvature opposite the
optica] surface desired in the lens being prepared, a
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vertical side wall extending from said bottom and at the other end
of said side wall an opening, there being at least one constant
sized key way on the exterior surface which follows said surface of
said hemispherical base, said key way being located below the molcl
cavity, said exterior surface of the hemispherical base being
capable of enya~ing an~ mating with a guide key in the
hemispherical shaped locating ring of a lens generating lathe.
Also disclosed is a process for manufacturing contact and
intraocular lenses with the aid of the disclosed mold.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a side view of a mold of this invention.
FIG. 2 is the top view of the mold of FIG 1.
FIG. 3 is a cross sectional view taken along line A-A of
FIG. 20
FIG. 4 is a cross sectional view taken along line B-B of
FIG. 2.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The molds of this invention and the process using the invented
molds are useful in prepariny contact lenses as generally defined
and intraocular lenses which for convenience are hereafter referred
to as IOI. For convenience in hereafter describing the invention,
unless otherwise specified, contact lenses and IOI, will be
collectively referred to as contact lenses.
In FIG. 1 the mold 20 has as the bottom surface 25 the
positive of a posterior optical surface which may be for a single
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vision correction (symmetrical radii), toric (non-symmetrical
radii), aspheric or bi~ocal contact lens or ~or an IOL. The
negative of the haptic portion of the IOL is formed in the bottom
surface 25 as the bottom surface 25 is formecl by the negative
master tool which is further clescribed below. Additionally, the
bottom surface 25 may be the positive of a rotationally symmetric
asphere such as parabola or an ellipse, or it may be a series of
concentric curves.
The circumference of bottorn surface 25 may terminate with a
series of variable diameters which will result in a rounded edge of
the lens blank (and subsequent lens) at the juncture of bottom
surface 25 and the inner side 24 vertical side wall 26 of cup-like
molding cavity. The configuration of the mold 20 at the junction of
bottom surface 25 and the inner portion 24 of wall 26 permits
molding of lens which will have extremely thin finished edges after
lathing of -the posterior surface of the lens.
In FIG. 2 the mold 20 is shown with two key ways 23 directly
across from each other on the exterior surface of hemispherical
portion 21 of the mold 20 base. Extending above the bottom surface
25 at the apex of the hemispherical portion 23 is the vertical side
wall 26, with outer side 22 and inner side 24, which encircles and
completes defining of the cup-like molding cavity for the contact
lens blank.
FIG. 3, taken along line ~-~ oE FIG. 2, illustrates the key
ways 23. The key ways 23 may be varied in number and size to meet
particular design requirements of the lense . Two key ways 23 are
preferred for molcl 20 although the number of key ways 23 may vary
from 1 to ~ or more clepending on the configuration and complexity
of the lens design. ~dditionally, the key ways 23 provide axial
alignment when required during the cutting of the lens. The actual
lens diameter within the mold cavity of FIG. 3 as defined by wall
26 can be adjusted either by providing a smaller cliameter for wall
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26 or by the addition within the inner wall 24 of a circular ridge
or ring having a diameter corresponding to the desired lens
diarneter and edge shape.
FIG. ~, taken along line B-~ of FIG. 2, illustrates the mold
at a point free of key ways 23.
The hemispherical portion 21 of mold 20 provides positive
thickness placement of the contact lens when the mold 20 is placed
in the hemispheric locating riny chuck o the lathe (not shown).
The above mold 20 and the process which follows are suitable
for the production of soft contact lenses, hard contact lenses,
hard gas permeable contact lens and IOL, including the haptic
portion(s) thereof.
A master negative tool, i.e. a tool for making the positive
bottom surface 25 of mold 20, having the curvature required on the
concave, posterior, surface of the finished lens is made from
glass, stainless steel or other materials which will withstand the
molding pressures and temperatures. Tools which have been
electroformed or electroplated or plated or vacuurn coated or
deposited may also be used. These tools are used to prepare the
molds 20 used in the process oE this invention.
The master negative tool is placed in a sleeve, a molding
grade of a resinous material such as polyimide, polycarbonate,
polymethyl methacrylate and related derivatives including the
corresponding acrylates, polymethylpentene, polyethylene,
polypropylene, polyvinyl chloride, or other heat so~tened molding
material is also placed in the sleeve. The chosen mold resinous
material must, of course, be compatible with the contact lens to be
cast. Among other materials the polyimides, e.g. nylon, and
polyvinyl chloride are cornpatible with lenses made with
hydroxyethyl methacrylate (H~M~). Nylon is also compatible with
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lenses made from N-vinyl pyrrolidinone. Either injection or
compression molding methods which are well known in the art may be
used to produce the negative resinous mold 20 of this invention.
A liquid or syrup monomer material containing a suitable
catalyst is placed over the bottom surface 25 of the mold 20 and
covered or blanketed to prevent evaporation of the monomer and or
inhibition of polymerization of the mixture. The liquid monomer is
then polymerized within the rnolcl to form a solid monolithic mass.
It is not necessary to remove the hardened plastic lens blank (not
shown) from the mold 20.
The mold 20 of this invention offers several advantages. First
the mold 20 precisely fixes the posterior curvature of the contact
lens. Secondly, it offers a convenient means of holding the lens
blank while cutting the anterior surface. More importantly,
because the mold's 20 key ways 23 must engage the keys or guide
pins of the lathe the precise location of the posterior lens
surface curves and lens blank thickness is established without
further measurement.
More important yet is the fact that the hemispherical shaped
base 21 in cooperation with key ways 23 permit the mold 20, while
still in the lathe, to be rotated about a given axis. This
rotation is accomplished by moving (or swinging) the mold 20 on
the keys or guide pins of the lathe hemispherical ring in either
direction. This movement of the mold 20 about khe axis can be
precisely controlled and calibrated by means now well known in the
lathing art. By so moving mold 20 in this controlled fashion two
or more surfaces may be cut on the anterior surface of the lens to
achieve the desired amount of prism and the like. Witho~lt the use
of the keys ancl key ways 23 the lens maker would have to resort to
difficult center lathing techniques to achieve the same results.
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The mold 20 and method of this invention also provide a convenient
way to generate prism or multiple curve segments as required for
segmented bifocal contact lenses and similar lenses.
The use of this invention lowers scrap rates because of
precise location and control means made possible by the mold 20.
~dditionally, production time is reducéd in cutting complex lens
configurations by elimination of conventional set up oEf center
lathing. In khe method o~ this invention the optic center can be
moved out of the center of rotation of the lathe by lateral
transposition of the axis.
While the mold 20 is shown with two key ways 23, other number
of key ways 23 may be used. It is noted that with only one key
and key way 23 the mold 20 does not as fully achieve in a
convenient fashion the benefits of this invention. When the lens
generating lathe is equipped with retractable keys or guide pins
then molcd 20 can be used very efficiently with four key ways 23 to
obtain very complex anterior surface lens configurations.
Mold 20 may be supplied to the lens generating lathe either
manually or by automatic ecluipment, e.g. pneumatic systems, as
desired.
. .
In a pneu-matic system a tube contains a series of molds 20,
each containing a lens blank. ~11 rnolds 20 are positioned in the
same manner and the cup-like cavity of each mold 20 faces a sensing
device and rnovement control. The tube has a diameter just greater
than the outside diameter of the rnold 20 so that air pressure may
be used to move mold 20 through the tube. A convenient number of
molcls 20 stored in each twbe would be about 20. When a signal is
sent from the lathe a solenoid opens and the movement control
allows mold 20 by air pressure via line to pass into the solenoid
and through to the lathe's hemispherical seating ring. When the
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solenoid valve has closed, mold 20 is fully seated and is
maintained therein by the air pressure which moved mold 20. While
the solenoid valve remains closed at the completlon of the lathe
cutting on signal from the lather the vacuum solenoid valve opens
and the applied vacuum removes mold 20. The cycle is completed
when vacuum solenoid valve closes cutting off the vacuum line and
allows air pressure to then return mold 20, now containing the cut
lens, to the lens tube. Thereafter the lens is polished, removed
from the mold 20 and inspected in the customary manner.
Because each time the mold 20 seats against the hemispherical
seating ring at the same place the cutting tool of the lathe can be
set at one position and successive lenses can be cut to the same
thickness. Previously the lathe operator needed to measure the
starting thickness of the lens blank and reset the cutting tool
each time in order to achieve lenses of an uniform thickness. By
this invention the lathe operator also avoids the remeasuremen-t of
each lens to assure the desired thickness has been obtained.
The advantages of this invention can also be obtained by
manually inserting mold 20 with lens blank into the hemispherical
seating ring. The manually inserted mold 20 is retained in place
by means of mechanically removing the space behind the mold to
bring it into fullest contact possible with the hemispherical
locating ring. The key ways 23 also act as drivers to avoid
slippage of the mold.
Any lens generating equipment, e.g., lathe, which can be
adapted with a longitudinal bore through the spindle can be used in
this invention. Examples o~ such lathes include those available
under the Hardinge ElSL and DV59 trademarks.
When the bottom surface 25 terminates with a series of
variable diameters to form an upwardly rounding junction with the
vertical side wall 24 oE the mold cavity, the resulting lens blank
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L86~3
will have a rounded edge. The rounded edge then permits the front,
or anterior, lens surface to be simultaneously lathe cut as
described above and finished in one operation.
The foregoing methods and examples have been described in
this speci~ication for the purposes oE illustration and not
limitation. ~any other modifications and ramifications will
naturally sugyest themselves to those skilled in the art based on
this disclosure. These are intended to be comprehended as within
the scope of this invention.
