U.S. patent application number 10/969632 was filed with the patent office on 2005-05-19 for methods and devices to control polymerization.
Invention is credited to Altmann, Griffith E., Armstrong, Lisa A., Beebe, Kevin D., Cox, Ian G., Huang, Horngyih, Lesczynski, Michael A., Martin, Arthur W., Moran, Michelle L., Papalia, Joseph, Ruscio, Dominic V..
Application Number | 20050104239 10/969632 |
Document ID | / |
Family ID | 22715490 |
Filed Date | 2005-05-19 |
United States Patent
Application |
20050104239 |
Kind Code |
A1 |
Altmann, Griffith E. ; et
al. |
May 19, 2005 |
Methods and devices to control polymerization
Abstract
A method and mold assembly to control the polymerization of a
molded article. In one embodiment, an amorphous posterior mold
comprising a non-critical surface having a controlled radius of
curvature is used to produce molded articles. In an alternate
embodiment, ophthalmic lenses are produced using a posterior mold
in which the concave surface of the non-critical surface is filled
with a liquid having a similar refractive index as the mold
material. In still another embodiment, a positive lens is placed at
a predetermined distance adjacent to the mold assembly to alter the
irradiation path to the mold assembly. In still another embodiment,
a positive lens is placed within the concave surface of the
posterior lens.
Inventors: |
Altmann, Griffith E.;
(Webster, NY) ; Armstrong, Lisa A.; (Webster,
NY) ; Beebe, Kevin D.; (Spencerport, NY) ;
Cox, Ian G.; (Mendon, NY) ; Huang, Horngyih;
(Penfield, NY) ; Lesczynski, Michael A.; (Honeoye
Falls, NY) ; Martin, Arthur W.; (Poughkeepsie,
NY) ; Moran, Michelle L.; (Fairport, NY) ;
Papalia, Joseph; (Webster, NY) ; Ruscio, Dominic
V.; (Webster, NY) |
Correspondence
Address: |
Bausch & Lomb Incorporated
One Bausch & Lomb Place
Rochester
NY
14604-2701
US
|
Family ID: |
22715490 |
Appl. No.: |
10/969632 |
Filed: |
October 20, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10969632 |
Oct 20, 2004 |
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09818919 |
Mar 27, 2001 |
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6827885 |
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60193904 |
Mar 31, 2000 |
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Current U.S.
Class: |
264/1.36 ;
264/1.38; 425/808 |
Current CPC
Class: |
B29D 11/00134 20130101;
B29D 11/00442 20130101 |
Class at
Publication: |
264/001.36 ;
264/001.38; 425/808 |
International
Class: |
B29D 011/00 |
Claims
1-13. (canceled)
14. A mold assembly comprising first and second mold portions, said
first mold portion having first and second opposing surfaces, said
first surface comprised of a concave surface having a controlled
radius of curvature and said second surface comprising an optical
lens-forming surface, said second mold having first and second
opposing surfaces, said first surface comprising an optical
lens-forming surface, wherein said mold portions matingly engage to
form a lens forming cavity therebetween said second surface of said
first mold and said first surface of said second mold.
15. The mold assembly of claim 14, wherein said first mold portion
comprised of an amorphous material
16. The mold assembly of claim 14, wherein said amorphous material
is polyvinyl chloride.
17-31. (canceled)
Description
BACKGROUND OF THE INVENTION
[0001] The present invention is directed toward controlled curing
of devices requiring optical cure. More specifically, the present
invention provides a method for curing optical devices such that
the devices undergo a more controlled polymerization, resulting in
a reduction in defects such as dimpling and warpage in the cured
device. In particular, the optical devices include ophthalmic
lenses including contact lenses, intraocular lenses, spectacle
lenses, corneal onlays and corneal inlays. More particularly this
method provides for a method to produce contact lenses having a
controlled cure profile.
[0002] It is often desirable to mold optical devices such as
contact lenses and intraocular lenses, rather than form the lenses
by machining operations. In general, molded lenses are formed by
depositing a curable liquid such as a polymerizable monomer into a
mold cavity, curing the liquid into a solid state, opening the mold
cavity and removing the lens. In particular, the mold cavity may be
formed by a mold assembly comprised of a posterior mold portion and
an anterior mold portion, each having a lens-forming surface. When
the posterior mold portion and anterior mold portion are mated, the
lens-forming surface of the posterior mold portion and the
lens-forming surface of the anterior mold portion form the
lens-forming cavity. The non-lens-forming surface of both mold
portions, herein referred to as non-critical surfaces, are
generally molded to have a similar radius (or radii) of curvature
as that of the lens-forming surfaces. While the lens-forming
surfaces are of optical quality, each having a central optical zone
and typically, at least a peripheral carrier zone, the only
requirement of the non-critical surface generally is a smooth
surface.
[0003] Polymerization is typically carried out by thermal means,
irradiation or combinations thereof. Traditionally, conventional
thermo-casting techniques require fairly long curing times and are
used when the resultant object is thick. Rods from which rigid gas
permeable lenses are lathed from or thicker lenses are often
thermally cured. Curing of lenses by irradiation, in particular,
ultraviolet (UV) irradiation, frequently offers short curing times.
The monomer is poured into a transparent mold having a desired
optical surface, and thereafter the UV light is radiated to the
monomer through the transparent mold to cure the photosetting
monomer.
[0004] A common material used as a mold material is polypropylene,
which is disclosed in U.S. Pat. No. 5,271,875 (Appleton et al.,
assigned to Bausch & Lomb Incorporated, the entire contents
herein incorporated by reference). The process disclosed in
Appleton et al., may be used to produce lenses with predictable and
repeatable characteristics.
[0005] The use of polypropylene may be desired with certain
lens-forming materials. Other lens-forming materials, however, may
cast just as well or better in other mold materials. As disclosed
in U.S. Ser. No. 09/312105 (Ruscio et al. and assigned to Bausch
& Lomb Incorporated, the entire contents herein incorporated by
reference), polyvinyl chloride absent any UV stabilizer provides a
suitable material for the posterior mold.
[0006] While the irradiation of the optical device from the light
source may be conducted in a uniform and parallel manner, the
material chosen for the mold portions may affect the pathways of
the light rays. For instance, some materials, such as thermoplastic
crystalline polymers, may diffuse the radiation, causing a
scattering of the light rays. Polypropylene is such a material.
Other materials such as polyvinyl chloride and polystyrene are
thermoplastic amorphous polymers, which permit an unhindered
pathway for the light rays during curing.
[0007] The radiation may also be reflected off the surface of the
glass or plastic mold materials. This may result in non-uniform
distribution of light intensity over the lens-forming material.
[0008] This invention recognized that the non-critical surface of
the posterior mold may act as an optical device, reflecting and/or
refracting the irradiation in a non-uniform pathway through the
mold portion. In particular, the geometry of the non-critical
surface of a posterior mold may affect the cure of the lens article
sandwiched between the posterior and anterior mold. For instance,
the non-critical surface of a posterior mold may be comprised of a
radius of curvature and an outer flat portion. The junction formed
at the intersection of the radius and flat portion may produce a
molding area in which the radiation does not penetrate well. This
would be similar to providing a shadow on the lens article. The
resultant lens would then have a circular area corresponding to the
junction(s) that may not be as completely cured as the rest of the
lens. Any junction formed at the intersection of different
geometries may produce "shadowing". The geometries need not
necessarily be spherical.
[0009] Additionally, the non-critical surface of the mold may
refract the radiation from the optical source. This may lead to
non-uniform curing speed of the ultraviolet curable resin. As a
result, since the curing is completed faster and more completely in
a portion receiving a high radiation intensity (in this instance,
the periphery portion of the lens) and slower in a portion
receiving a low irradiation intensity (the central portion,
respectively), a stress is generated in the cured resin layer. This
stress may deteriorate the precision of the optical device face.
Additionally, since the faster curable portion receiving higher
radiation intensity is cured with absorption of the surrounding
uncured resin in order to compensate for the contraction of resin
resulting from curing, the slower curable portion (which receives
lower radiation intensity) may show defects such as shrinkage. In
particular, in the case of contact lenses and spectacle lenses,
this can produce lenses with unacceptable optical aberrations
caused by uneven curing and stress. "Dimpling" or warpage of the
contact lens is a common problem caused by uneven curing. In
dimpling, the apex of the lens is flattened or slightly concave in
shape. Warpage is generally seen as the inability of the edge of a
lens to have continuous contact with the molding surface upon which
it contacts. Other drawbacks seen with plastic spectacle lenses
include "striations", which are caused by uneven curing and stress.
Thermal gradients form in the gel-state, which produce convection
lines ("striations") that become frozen in place and cannot be
dispersed.
[0010] U.S. Pat. No. 4,166,088 (Neefe) discloses a method of
controlling the polymerization of cast optical (plastic or contact)
lenses. The mold section on the bottom is a lens which focuses UV
light to the center of the cavity. The bottom mold. must have a
thickness which corresponds to the focal length of the refractive
surface so that the UV light rays converge at the center of the
monomer being cured. Neefe also requires an aluminum reflector on
the outer surface of the top mold to reflect light back through the
monomer.
[0011] U.S. Pat. No. 4,534,915 (Neefe) discloses the use of a
convex positive refractive power cylinder lens to provide a band of
actinic light to a rotating lens monomer. The center of the spin
cast lens receives the most radiation, the area adjacent to the
center receives less while the periphery receives still less
radiation. This allows for the outer portion of the spin cast lens
to migrate inward as the lens shrinks during the curing process. A
fresnel lens or a Maddox rod may also be used to provide the narrow
high-energy line of actinic light.
[0012] U.S. Pat. 4,879,318 (Lipscomb et al.) discloses the use of
mold members formed from any suitable material that will permit UV
light rays to pass through. To aid in the even distribution of the
UV light, the surfaces of the molds are frosted. In one embodiment,
a Pyrex glass plate is used to filter out UV light below a certain
wavelength. Lipscomb et al. found that if incident UV light is not
uniform throughout the lens, visible distortion pattern may appear
in the finished lens. Lipscomb et al. solved this problem by
including additives in the lens forming composition to reduce the
distortions. The ophthalmic lenses are formed from plastic.
[0013] U.S. Pat. 4,919,850 (Blum et al.) discloses a method for
making plastic lenses in which the liquid lens material is
dispensed into the mold cavity and put into a heated bath for a
partial thermal curing. After a period of time, the mold (while
still in the liquid bath) is subjected to UV light for an
additional period of time. The liquid bath disperses the UV light
sufficiently to avoid stresses and other adverse effects on the
lens ultimately formed that may be caused by uneven exposure to the
UV light. The mold may also be rotated while in the bath or the
bath may include an aerator to enhance the dispersion of the UV
rays. By rotation of the mold and aeration of the bath,. the
surface of the mold is also kept free of any debris which may
otherwise channel the UV light. Additionally, a reflective surface
provided on the one of the molds forms may reflect UV light back
through the lens material being cured.
[0014] U.S. Pat. No. 4,988,274 (Kenmochi) discloses irradiating the
central portion of the mold cavity containing the lens-forming
material to initiate a photocuring reaction. The area of the light,
in the shape of a ring, is enlarged until the lighted area reaches
the periphery of the lens-forming material. A variable power lens,
including a fresnel lens, may be used to align the light. The
lens-forming material in the center of the mold cavity is cured
first which causes the lens-forming material around it to shrink.
The shrunk volume of lens-forming material is supplemented with
additional uncured lens-forming material. The variable power lens
allows for adjustment of the ring-shaped light.
[0015] U.S. Pat. No. 5,135,685 (Masuhara et al.) discloses the use
of a conveyor or other moving device to continuously move objects
to be irradiated by a multiplicity of aligned sources of visible
light. The movement of the irradiated objects may be linear or
curved movement on the same plane or upward or downward
movement.
[0016] U.S. Pat. No. 5,269,867 (Arai) discloses a method for
producing glass lenses with a coating on one side. The coating is a
resin layer that is cured with UV light. The resin is dropped onto
a metal mold (with a reflective surface) and the glass lens placed
on the resin. The resin is interposed between the lens and the
metal mold. UV light is provided through the glass lens, curing the
resin. A filter may be used to evenly distribute the UV light.
Without the filter, the reflection of the metal mold and the glass
lens result in non-uniform distribution of UV light and non-uniform
curing speed. The center of the resin cures faster than the outer
perimeter, causing defects such as shrinkage in the resin.
[0017] U.S. Pat. No. 5,529,728 (Buazza et al.,) discloses a method
of curing a plastic eyeglass lens. The method comprises placing a
liquid polymerizable composition within a mold cavity defined by
mold members and a gasket. A first set of UV rays is directed to
one of the mold members. The gasket is removed and a second set of
UV rays is directed to the lens. Buazza et al., further discloses
the use of a filter which includes a plate of Pyrex glass to
diffuse the UV light so that it has no sharp intensity
discontinuities. To produce a positive lens, the UV light intensity
is reduced at the edge portion so that the thicker center portion
of the lens polymerizes faster than the thinner edge of the lens.
Mold members of Buazza et al., are preferably precision ground
glass optical surfaces having UV light transmission characteristics
including casting surfaces with no surface aberrations, waves,
scratches or other defects.
[0018] None of the above art completely solves the problems which
occur when using a mold assembly in which one mold portion is made
from an amorphous material and acts as an optical device. The
resultant lens made from this particular mold assembly may have
defects such as dimpling and warpage.
SUMMARY OF THE INVENTION
[0019] The present invention is a method for photocuring cast
articles such as ophthalmic lenses in which defects in the cured
article are reduced. By altering the pathway by which irradiation
rays reach the article to be cured, defects can be reduced. By
controlling the relative intensity of radiation upon a particular
portion of lens-forming material, the rate of polymerization taking
place at various portions of the lens can be controlled. This
method is particularly suited for use with mold materials which are
amorphous.
[0020] One embodiment of this invention comprises altering the
radiation rays by at least partially neutralizing the optical
affects of the non-critical surface through which the rays
initially penetrate. This can be accomplished by filling the
non-critical surface cavity of the posterior mold with a liquid,
such as water or glycerin.
[0021] Another embodiment of this invention comprises reshaping or
removing any junctions formed between different geometries (e.g. a
radius of curvature and flat surface portion) used to form the
non-critical surface. The non-critical surface of the posterior
mold may then be comprised of a controlled radius of curvature,
eliminating any shadows or areas which the irradiation rays may not
penetrate evenly. The controlled radius may be spherical or
aspherical, provided that the surface is smooth and continuous.
[0022] In still another embodiment of this invention, the radiation
path from a light source is altered so as to obtain a desired cure
profile across the mold cavity. This results in controlled cure
gradient across the cast article. The radiation path may be altered
in various ways, including the use of an optical element. The
optical element may be a positive or negative lens.
[0023] In the preferred embodiment, the optical element is a
positive lens which is placed at a predetermined distance above the
posterior mold. The positive lens converges radiation rays,
preferably ultraviolet (UV) radiation, passing through the mold and
increases the energy available to the cured article. The
distribution of irradiation rays radiates from the center of the
mold. This distribution reduces the cure gradient across the lens,
which reduces or removes any residual stress induced during curing.
The result is a cured article such as a contact lens having an
acceptable apex in the central portion of the lens. The positive
optical element allows control of the illumination intensity
profile reaching various sections of the contact lens. Stress
developed by uneven intensity profiles can be removed or
introduced.
[0024] It is further preferred that the radiation path is altered
by use of an aspheric condenser lens such that the light rays
passing through the posterior lens mold is distributed radially.
The aspheric condensing lens is placed at a certain distance from
the mold and preferably has a plano back. The lens may be any lens
that focuses light to a certain desired area.
[0025] An alternate method of altering the radiation path is
placement of an optical element into the non-critical surface
cavity of the posterior mold. In particular, the radiation can be
altered by placement of a lens in the shape of a plug into the
non-critical surface cavity of the posterior mold. Preferably the
lens is a solid asymmetric convex lens and the material from which
it is formed is amorphous.
[0026] The ophthalmic lenses formed from these methods are
relatively free from defects such as dimpling and warpage.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIG. 1 is a cross-sectional elevational view of a posterior
mold section assembled with an anterior mold section;
[0028] FIG. 2 is a perspective exploded view of a mold assembly
including a contact lens;
[0029] FIG. 3 is a cross-sectional elevational view of a posterior
mold section showing light diffusion through the mold section;
[0030] FIG. 4 is a cross-sectional elevational view of a posterior
mold section showing the non-critical surface having a controlled
radius of curvature;
[0031] FIG. 5 is a cross-sectional elevational view of a posterior
mold section showing the non-critical surface filled with a
liquid:
[0032] FIG. 6 is a cross-sectional elevational view of a posterior
mold section showing light diffusion through a plano-back aspheric
lens suspended above the posterior mold section; and
[0033] FIG. 7 is a cross-sectional elevational view of a posterior
mold section showing light diffusion through an optical lens
contained within the cavity of the posterior mold section.
DETAILED DESCRIPTION OF THE INVENTION
[0034] The present invention is useful for the method of making
ophthalmic lenses. Preferred embodiments include the method of
making intraocular and contact lenses.
[0035] As seen in FIGS. 1 and 2, mold assembly 5 defines mold
cavity 40 for casting lens 30, including anterior mold portion 10
for defining the anterior lens surface 32 and posterior mold
portion 20 for defining the posterior lens surface 34. Anterior
mold 10 has lens-forming surface (critical surface) 12 and opposing
non-critical surface 14. Posterior mold 20 has lens forming surface
22 and opposing non-critical surface 24. When posterior mold
section 20 is assembled with an anterior mold section 10,
lens-forming cavity 40 is formed between posterior mold section
lens forming surface 22 and anterior mold section lens-forming
surface 12. As discussed in Appleton et al., lens 30 formed from
this mold assembly include a central optical zone 42 and a
peripheral carrier zone 44. The peripheral zone 44 has a
substantially greater volume than the optical zone 42 and may
include a tapered edge.
[0036] As illustrated in FIG. 1, rays 25 from optical source 1
irradiate non-critical surface 24 of posterior mold portion 20. The
index of refraction of rays 25 changes as the rays pass through air
and then through a solid material.
[0037] The preferred material for posterior mold portion 20 is an
amorphous material such as polyvinyl chloride (PVC) or polystyrene.
Other suitable materials include an amorphous copolymer of ethylene
and a cyclic olefin (such as a resin available under the tradename
of Topas, from Hoechst Celanese Corporation), standard glasses,
synthetic polymers with glass-like properties such as polymethyl
methacrylate, polycarbonate, acrylonitrile copolymer (such as resin
available under the tradename of Barex), TPX (poly-4-methyl
1-pentene) and polyacrylonitrile. Accordingly, it is preferred that
anterior mold 10 is amorphous although other crystalline
thermoplastic material such as polypropylene may be used.
[0038] The optical or radiation source may be actinic, electron
beam, laser or radioactive source, but is preferably ultraviolet
lamps which irradiates the monomer. Visible light or infra-red
light may also be used. Radiation may also be from a high intensity
UV source. Additionally, combinations of light irradiation and
thermal means may be used. Unless specified, the term "light" or
"rays" will refer to any actinic wavelength or range of
wavelengths.
[0039] Posterior mold 20 can further be described by its optical
parameters. In particular, based on the parameters of a posterior
mold used to produce commercially available lenses but using an
amorphous material such as PVC, one can calculate the powers of
each surface of the mold: non-critical surface radius 6.0 mm
(R.sub.1), critical surface radius of -8.0 mm (R.sub.2), index of
refraction of PVC mold material 1.5 (n.sub.2), index of refraction
of air 1.0 (n.sub.1), center of thickness of the mold 2.0 mm (t)
and index of refraction of lens-forming monomer of 1.4 (n.sub.3).
While HEMA (2-hydroxyethylmethacrylate) is a preferred monomer, any
lens-forming polymerizable material may be used. Especially
preferred are materials that are capable of free radical
polymerization. Preferred materials include silicone and
methacrylate hydrogels. Preferred examples of applicable materials
are disclosed in U.S. Pat. Nos. 5,610,252 and 5,070,215 (Bambury et
al., assigned to Bausch & Lomb Incorporated, the entire
contents herewith incorporated by reference).
[0040] The posterior mold is a negative lens with essentially all
of its negative power coming from the non-critical surface. The
negative power of the mold causes incident UV rays to diverge as
they pass through the mold which leads to a reduction in intensity
at the center of the lens-forming cavity. The power of the
posterior mold can be described by the following equations:
[0041] Power of non-critical surface:
.phi..sub.1=(n.sub.2-n.sub.1)/R.sub.1=-83.333 D
[0042] Power of critical surface:
.phi..sub.2=(n.sub.3-n.sub.2)/R.sub.2=+12.5000 D
[0043] The total power (.PHI.) of the mold is:
.PHI.=.phi..sub.1+.phi..sub.2-(t/n.sub.2).phi..sub.1.phi..sub.2=-69.444
D
[0044] Non-critical surface 24 of posterior mold 20 is typically
spherical with a radius of curvature that is concentric with
equivalent radii of lens-forming surface 22. This keeps the
thickness relatively constant across the posterior mold. This
concentric requirement forces posterior mold 20, especially when
posterior mold 20 is an amorphous material, to be a substantially
negative lens. As illustrated in FIG. 3, rays 25 passing through
non-critical surface 24 of posterior mold 20 are refracted outward,
away from the center optical portion and toward the peripheral
carrier zone of the lens (not shown) being cured. This may result
in an uncontrolled curing profile of the lens, i.e., one portion of
the lens may cure faster or more completely than another portion.
Often lenses with uncontrolled cure profiles are warped or
demonstrate dimpling.
[0045] FIG. 3 also illustrates another cause of uncontrolled cure
profiles. It is common for non-critical surface 24 to be comprised
of at least two radii of curvature. As seen in FIG. 3, junction 7
is formed at the intersections of portion A and portion B. Portion
A defines radius R.sub.a. Rays 25 from optical source 1 are blocked
by junction 7 from passing through mold 5. This shadow is indicated
by darkened area 8. This results in a circular ring of lens-forming
material that is not as fully cured as areas outside area 8.
[0046] One way to avoid "shadows" of uncured (or partially cured)
lens-forming material is to control or remove the junction. This
can be accomplished by molding the non-critical surface as a
controlled surface or one that is formed without any junctions. An
example is shown in FIG. 4. Rays 25 would not be impeded from
passing through non-critical surface 124. Use of posterior mold 120
with non-critical surface 124 having a controlled surface as part
of a contact lens mold assembly would produce improved lenses
having a better cure profile. Non-critical surface 124 may be
spherical or aspherical.
[0047] FIG. 5 illustrates the neutralization of the optical effect
of the posterior mold. This change is accomplished by the changing
the way energy goes through mold 20. Concave surface 26 is formed
by the non-critical surface 24. By placing a predetermined amount
of liquid 50 in concave surface 26, the amount of reflection or
refraction off of the non-critical surface 24 is reduced. The
distribution of light rays emerging through lens-forming surface 22
is more even, resulting in a more controlled cure profile of cured
lens 30. In the preferred embodiment, fluid 50 forms convex
meniscus 52 with upper surface 28 of posterior mold 20. As shown,
rays 25 from optical source I pass through liquid 50 and
non-critical surface 24 in a parallel manner. The effects of any
junctions (as previously in illustrated in FIG. 3) or any surface
irregularities are negated. Stress in the resultant lens is reduced
and the lens exhibits a controlled cure profile.
[0048] The use of liquids in this manner can also increase the
effective intensity of irradiation rays reaching the monomer
surface.
[0049] In the preferred embodiment, the liquid used to fill concave
surface 26 has a refractive index not substantially different than
the mold material. Any liquid can be used. Especially preferred is
water, glycerin or mixtures thereof.
[0050] Another embodiment of the invention is illustrated in FIG.
6. In this embodiment, an optical device made preferably from
optical glass (i.e., free from internal strains, bubbles and other
imperfections) is used to control the curing profile of the cast
article.
[0051] By placing the optical device at a predetermined distance
above the mold assembly, rays 25 from optical source 1 can be
directed in a desired direction. Aberration, defined as a blurring
and loss of clearness in an image, can also be limited by choosing
the correct optical device. The optical device would converge the
rays to a single focus point. For instance, a glass condenser lens
60 can shorten the focal length and cancel spherical aberration.
Rays 25 pass through condenser lens 60 and concentrate the energy
of the rays toward center 27 of mold 20. Although FIG. 6 shows the
preferred embodiment (optical device 60 is an aspheric plano-back
lens with the aspheric surface 62 toward optical source 1), optical
device 60 may be inverted, having the aspheric surface 62 toward
non-critical surface 124 of mold 120. Preferably, optical device 60
is positioned above mold assembly 5 and is held within a clamping
device (mold assembly and clamping device not shown). Other
embodiments are possible depending on the lens or lenses chosen.
For instance, examples of aspheric condenser lenses include those
with convex or concave backs. While the preferred embodiment is a
simple or single lens of high magnification, compound lenses
forming an optical system may be used to achieve the desired focal
length and magnification. The compound lenses may include
condensing or magnifying lenses or combination thereof.
[0052] An alternate embodiment is the use of a solid asymmetic
convex lens or plug made from an amorphous material. The lens
provides a uniform and magnified light source when inserted into
the posterior mold cavity, i.e., adjacent to the non-critical
surface of the posterior mold.
[0053] As shown in FIG. 7, asymmetric convex plug 130 is inserted
into concave surface 26 of posterior mold 20. Lens 130 converges
rays 25 from optical source 1, which results in an increase of
energy available to the lens-forming material (not shown). As seen
in FIG. 7, it is not necessary for surface 132 of plug 130 to have
an identical shape as non-critical surface 24. In fact, there may
be a slight gap at periphery 27 of concave surface 26. Non-critical
surface 24 may be a controlled surface as previously discussed or
may have junctions present.
[0054] A preferred amorphous material includes Topas, an amorphous
copolymer of ethylene and a cyclic olefin. Preferred are the
following random copolymers: 1
[0055] wherein R is hydrogen or C1-C4 alkyl, preferably
hydrogen;
[0056] Each R' is independently hydrogen or C1-C4 alkyl, preferably
hydrogen or methyl; and
[0057] X and y are at least 1.
[0058] These materials are available from Hoechst Celanese
Corporation, Summit, N.J., USA and the lens is typically
lathed.
[0059] Topas is well adapted for UV curing processes. As an
example, this copolymer has very high light transmissibility.
Therefore, for curing operations employing irradiation-induced
polymerization, the higher transmissibility of the plug material
permits a more efficient curing process. Topas was the subject of
prior application U.S. Ser. No. 09/260860 (Ruscio, assigned to
Bausch & Lomb Incorporated) wherein the material was disclosed
as a molding material.
[0060] In an alternate embodiment, one may choose to introduce
predetermined stress profiles to a lens, rather than remove them.
In a specific instance, it may be desirable to form a lens having a
specific shape which would alter the fitting of the lens to the
eye, such as increasing the lens movement when worn on the eye. A
specific parameter which could be stress-induced is edge lift which
causes the edge of the lens to be slightly raised off the eye.
Inducing stress to a lens can be performed by altering the
parameters of the optical devices altering the irradiation
pathway.
[0061] The following examples serve to illustrate the use of
optical devices to affect the cure profile (i.e., SAG measurements)
of an ophthalmic lens formed in a mold assembly.
EXAMPLE 1
[0062] A series of HEMA lenses was cast molded using posterior and
anterior molds made from a non-UV stabilized PVC resin. The
posterior mold concave surface of lot 2 was filled with glycerol;
the posterior mold concave surface of lot 3 was filled with water.
After casting, the mold assemblies were separated and lenses were
hydrated and measured. Each lot had five lenses.
1 TABLE 1 Lot # SAG (mm) 1 (control) 3.018 2 3.596 3 3.600
[0063] Lenses made with water or glycerol in the posterior cavity
showed an increased SAG measurement when compared to the control
lenses. The lots with increased SAG measurements showed a decrease
in the number of lenses exhibiting dimpling.
EXAMPLE 2
[0064] A series of HEMA lenses was cast molded using posterior and
anterior molds made from a non-UV stabilized PVC resin. The mold
assemblies were separated and lenses were hydrated and measured.
Lot 1 had 89 lenses, Lot 2 had 69 and Lot 3 had 27. Lot 3 had a
controlled non-critical surface (no junctions present). A 58.8 D
magnifier lens was used as the optical lens.
2TABLE 2 Non-Critical Clamp Surface Plate Power of Average Lot No.
Posterior Mold Treatment Contact Lens SAG 1 (control) Standard No
-6 3.298 Surface, Bevel condensing lens 2 Optical Quality 58.8 D -6
3.372 Surface, Bevel condensing lens 3 Controlled 58.8 D -6 3.451
curve condensing lens
[0065] The lenses cured with a magnifying lens showed an increase
in SAG measurements as compared to the control lenses (lot 1).
EXAMPLE 3
[0066] A series of HEMA lenses was cast molded using posterior and
anterior molds made from a non-UV stabilized PVC resin. The mold
assemblies were separated and lenses were hydrated and measured.
Each lot had 5 lenses. Lot 1 was a control lot. An asymmetric
convex plug having a power of 117 D made of Topas was inserted into
the posterior concave surface of lot 2. The surface of the plug
toward the optical source had a radius of 7.00 mm and the surface
of the plug facing the non-critical surface of the mold had a
radius of 8.5 mm. The SAG of the plug was 4.68 nm.
3 TABLE 3 Lot No. SAG (average) 1 (control) 3.534 2 3.658
[0067] The lenses made using an asymmetric convex plug made of
Topas inserted showed an increase in SAG measurement and a lower
incidence of dimpling. Overall, improved lenses were produced using
the Topas insert.
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