Method for forming plastic optical quality spectacle lenses

A fast, relatively inexpensive method and simple is disclosed for producing a finished plastic multifocal or progressive lens from a preformed lens which has a predetermined lens correction (i.e., curvature or prescription) at its optical center. The disclosed method produces a finished lens which has a multifocal or progressive region without changing the lens correction at the optical center of the lens.

FIELD OF THE INVENTION 
The present invention relates to methods for quickly and inexpensively 
producing multifocal and progressive plastic optical quality spectacle 
lenses from preformed lenses of a given prescription. 
BACKGROUND OF THE INVENTION 
In manufacturing lenses, and particularly lenses for eyeglasses, the use of 
plastics is often desirable due to their light weight and durability. 
Plastic lenses also provide relatively economic vision correction. Methods 
for producing plastic lenses of various prescriptions are well known. 
Applicant's U.S. Pat. No. 4,873,029, 4,919,850 and 5,028,538, which are 
incorporated herein by reference as if fully set forth, disclose methods 
for making plastic lenses of ophthalmic quality for eye glasses. 
Prior methods of others have, however, failed to provide fast and economic 
means for manufacturing high index-quality, reliable multifocal (e.g., 
bifocal, trifocal, etc.) or progressive plastic lenses. U.S. Pat. No. 
3,248,460 (the "'460 patent") discloses means for casting plastic lenses 
from thermosetting or thermoplastic materials wherein a plastic blank 
having significantly less curvature than required for the full intended 
prescription of the lens is used as a base onto which an additional layer 
of material is cast. The '460 patent employs a conventional optical gasket 
to provide space between the plastic blank and the mold and to hold the 
resin material in the cavity created thereby. The additional layer of 
material changes the curvature of the resulting lens over the vast 
majority of its surface, thereby changing the prescription of the 
resulting finished lens to the power required. The material in the '460 
patent is cured by heat. However, such heat curing process requires 
heating over a period of more than 12 hours, thus making the formation of 
the lens a long, drawn-out process. 
U.S. Pat. No. 3,946,982 also discloses methods for casting an entire lens 
surface with a prescription layer using a conventional optical gasket. 
Conventional industrial lens casting techniques require the use of 
"conventional optical gaskets" which hold together the components used to 
cast the lens, allow for thickness to be cast into the resultant lens, and 
create a substantially air-tight environment for the casting process. In 
most cases these conventional optical gaskets can only be used one time 
and then are discarded. Therefore, a significant number of different 
gaskets must be maintained. 
In-office lens casting is even more demanding with regard to the number of 
different conventional optical gaskets needed and the inventory necessary 
to produce different finished lens prescriptions. In one such system, 
approximately 737 conventional optical gaskets must be maintained in 
inventory and constantly replaced (after one use) to allow production of 
all prescriptions. Approximately 200 "optical center movers" (OCMs) must 
also be inventoried to relocate or decenter the optical center. These OCMs 
are also not reusable and must be constantly replaced. The need to 
maintain and replace this varied inventory of conventional optical gaskets 
and OCMs contributes significantly to the cost of lens casting. In the 
case of in-office lens casting these components can account for 
approximately 32% of the materials cost of casting a lens using such a 
system. 
Others have tried to manufacture multifocal or progressive plastic lens, 
using a lamination technique. Such a technique joins a preformed plastic 
section to another cured plastic prescription lens. A portion of the 
preformed section defining a multifocal or progressive region of the 
finished lens is joined to the prescription lens by adhesive. Such methods 
have proved to be technologically cumbersome and uneconomical, however, 
due to the expense of maintaining a large number of preformed lens 
portions such that all of the possible permutations of patient primary 
correction and multifocal correction can be formed. Furthermore, the 
optical quality of such lenses has been suspect because of the difficulty 
of matching the surfaces of the preformed lens and the wafer. 
In the case of in-office lens casting which casts the finished 
prescription, and to a lesser extent industrial lens casting which casts 
primarily semi-finished lens blanks, a prism effect may also need be 
accommodated in the molding process. Present methods for creating prism in 
plastic lenses have also proven cumbersome. "Prism" is created in lens 
designs to shift the optical center of a lens from the geometric center of 
the lens to some other preferred location. Also in the case of progressive 
lenses, it is used for a compensating base-down prism to offset the 
base-up prism produced by the progressive mold. In multifocal lenses it is 
advantageous to shift the optical center of the distance portion of lens 
to more closely align with the multifocal region of the lens, thus easing 
the wearer's transition from the distance prescription to the prescription 
of the multifocal region (near region) of the lens. 
When casting a finished lens, prism is cast into the lens in ways that are 
well known in the art. However, in cases of semi-finished lenses, in order 
to create prism the lenses must be surfaced to produce both the desired 
prismatic effect and the correct optical prescription. Surfacing requires 
additional equipment and time which make such methods less than desirable 
for making lenses quickly and inexpensively from start to finish. 
When reviewed from an overall perspective of lens production, starting with 
liquid resin and ending with a finished lens mounted in the frame, the 
conventional process is extremely complex, long and arduous. Curing has 
required 12-14 hours; wholesale lab surfacing of the cured lens semi 
finished blank, approximately an additional 30 minutes; and finishing the 
lens, another approximately 30 minutes. Thus, the overall lens 
manufacturing process can require 13-15 hours, making it difficult to 
quickly provide prescription lenses on request, unless one stocks 
semi-finished blanks and utilizes surfacing equipment, both of which add 
tremendously to the overall cost of production which is ultimately passed 
on to the consumer. 
It would, therefore, be desirable to provide a faster, more economical 
method and much simpler for producing multifocal or progressive lenses. It 
would also be desirable to provide a method for changing the prescription 
or lens design (i.e., multifocal, progressive, prismatic effects, etc.) of 
a preformed prescription plastic lens which is both fast and inexpensive. 
Preferably, such method should produce lenses without employing a 
conventional optical gasket. 
SUMMARY OF THE INVENTION 
The present invention relates to a fast, simpler and relatively inexpensive 
method for providing a multifocal or progressive region on a preformed 
plastic optical quality spectacle lens to produce a resulting finished 
multifocal or progressive lens. The preformed lens has a predetermined 
lens correction (i.e., curvature or prescription) at its optical center 
which is unchanged in the finished lens. The preformed lens can be a 
finished lens (having a curvature or correction on front and back 
surfaces) or a semi-finished blank lens (having a curvature or correction 
on only one surface). 
The preformed lens can also be "pre-edged" into the desired shape of the 
lens such that the resulting lens is ready for mounting after the casting 
process without need for additional edging. In certain preferred 
embodiments, the pre-edged preformed lens can be used with a pre-edged 
mold such that the resultant lens is formed to the desired shape without 
the need for additional edging. When a disposable mold is employed, the 
preformed lens and disposable mold can be edged together after the optical 
center, multifocal segment or progressive region, and astigmatic axis are 
properly aligned and used to cast a final lens of the desired shape 
without significant flashing. In some of such embodiments, a special 
gasket could be employed which employs a bevel which provides a groove or 
bevel around the edge of the resultant lens for directly mounting the lens 
in glasses frames. Alternatively, the pre-edged preformed lens could be 
used with a mold which is significantly larger than the preformed lens, 
such that the resultant lens is made with very little flashing. 
By casting an optical segment or other multifocal or progressive region on 
the surface of the preformed lens myriad lens designs can be achieved 
quickly and inexpensively. Such method decreases the large number of 
different mold combinations usually needed to cast multifocal and 
progressive lenses. Also, in certain embodiments, it eliminates the large, 
expensive and cumbersome number of conventional optical gaskets and OCMs 
customarily used in in-office lens casting. In most instances, the lenses 
produced according to the invention also do not require additional 
surfacing to achieve the proper prescription and can eliminate the 
additional step of surfacing prism into the finished lens to relocate the 
optical center. The methods of the present invention allow production of 
bifocal, multifocal, progressive and aspheric lenses, among others, from 
previously formed prescription lenses. In essence, the preformed lens 
serves as a mold which is consumed during the casting process and forms a 
part of the finished lens. 
The multifocal or progressive region can be cast onto the preformed lens 
alone or in combination with an additional thin non-prescription layer of 
resin which acts as a carrier for the resin defining the multifocal or 
progressive region. It should also be noted that the preformed lens and 
mold used in practicing the various embodiments of the present invention 
need not have the same base curve. 
The methods of the present invention can also be used to convert preformed 
single vision, multifocal or progressive lenses into aspheric lenses by 
adding material to the lens surface. In such embodiments, the cavity 
formed by the preformed lens and the molds corresponds to the desired 
shape of the surface needed to create the aspheric effect. 
In contrast with traditional lens casting methods, the methods of the 
present invention provide lenses relatively quickly and at significantly 
less cost. Using the methods disclosed herein that use ultraviolet light 
curing, curing requires approximately 5-30 minutes, no surfacing is 
required, and finishing requires another approximately 30 minutes. Thus, 
the present invention provides means for producing optical quality 
multifocal and progressive lenses in approximately 1 hour or less, 
starting with liquid resin and ending with the finished lens in the frame. 
This allows delivery of prescription lenses upon request and without 
having the patient wait a significant time. Due to the ability to cast 
without a conventional optical gasket, in some cases, the methods of the 
present invention even allow the preformed lens to be finished (i.e., 
edged and tinted) for the exact customer frame before adding the thin 
non-prescription carrier layer and multifocal or progressive surface. 
Various other advantages of the methods of the present invention and lenses 
made thereby will be evident from the detailed description of certain 
embodiments below.

DETAILED DESCRIPTION OF THE INVENTION 
The method for making a finished lens having a multifocal or progressive 
region utilizes a mold; an optical quality resin composition; a preformed 
plastic lens having a predetermined lens correction at its optical center. 
The preformed lens is contacted with the mold to form a cavity for 
enclosing the resin composition. The resin is then cured and shaped by the 
cavity which corresponds to the shape of the multifocal or progressive 
region. The lens correction at the optical center of said resulting lens 
is substantially the same as the predetermined lens correction at the 
optical center of the preformed lens. 
The methods disclosed herein may cast a thin, non-prescription layer of 
material over some or all of the preformed lens surface in addition to 
casting the multifocal or progressive region alone. Such additional layer 
acts as a "carrier" for the multifocal or progressive surface without 
affecting the predetermined distance prescription of the preformed lens. 
In such cases, the cavity may also correspond to the shape of such 
carrier. 
FIGS. 1-3 depict the formation of lenses in accordance with the methods 
disclosed herein. Mold 13 and preformed lens 11 form a cavity 14 which 
contains a portion of the optical resin composition. In FIGS. 1 and 3, 
cavity 14 defines a multifocal (bifocal) segment 12. In FIG. 2, cavity 14 
defines a segment 12 and a carrier layer 16 (which does not change the 
distance prescription of the preformed lens). When cured, the segment 
and/or carrier harden and bond to the preformed lens to produce the 
finished lens. 
The mold and the preformed lens may be contacted (a) after the resin 
composition is placed onto the preformed lens, (b) after the resin 
composition is placed onto the mold, or (c) before the resin composition 
is applied to either component (i.e., the resin composition is dispensed 
into the cavity formed by the mold and the preformed lens). 
The cavity formed by the preformed lens and the mold is shaped or 
configured, among other purposes, (1) to correspond to the desired shape 
of the multifocal or progressive region of the finished lens, and (2) to 
maintain the lens correction at the optical center of the resulting lens 
substantially the same (preferably the same) as the predetermined lens 
correction at the optical center of the preformed lens, even when the 
surface of the preformed lens is cast within a carrier layer. This is even 
true, as described herein, when the optical center of the resulting lens 
has been shifted to achieve the proper alignment with respect to 
multifocal and progressive prescriptions. In certain embodiments, at least 
one surface of the preformed lens or mold is masked prior to contacting 
the lens with the mold. The cavity can also be shaped to correspond to the 
shape of a resultant prism region which creates prism in the resulting 
lens. 
The finished optical lenses made in accordance with such methods provide a 
first lens correction at their optical centers and have a second region 
removed from the optical center (i.e., the multifocal or progressive 
region) which provides a second lens correction. 
A method is also provided for forming such a multifocal lens in multiple 
stages. A preformed lens is first cast as described above to provide an 
intermediate lens having an intermediate lens correction at the second 
region, the magnitude of which is between the magnitudes of the first lens 
correction and the second lens correction. The intermediate lens is then 
cast again as described to provide a lens curvature at the second region 
corresponding to the second lens correction (and a carrier, if used). 
Lenses made in accordance with the present invention are also disclosed in 
which addition of a multifocal optical segment creates a beneficial 
positive transition in the finished lens. Such lenses provide at least a 
third lens correction and a fourth lens correction. The third lens 
correction is provided by a third region adjacent to the optical segment 
and is located between the optical center of the preformed lens and the 
center of the segment. The fourth lens correction is provided by a fourth 
region within the segment and is located between the optical center of the 
preformed lens and the center of the segment. As described further below, 
the magnitude of the third lens correction is between the magnitudes of 
the first lens correction and the fourth lens correction; and the 
magnitude of the fourth lens correction is between the magnitudes of the 
second lens correction and the third lens correction, such that a gradual 
discontinuous change in prescription is provided. This phenomenon has been 
observed mainly in connection with addition of a flat top optical segment. 
The methods of the present invention can be used to add a multifocal or 
progressive region to the front lens surface, the back lens surface or 
both. Preferably, the curvature of the lens is changed over only a small 
portion of a surface of the preformed lens to form an "optical segment". 
The methods of the present invention can be used to form lenses of almost 
any multifocal or progressive optical configuration including without 
limitation bifocals, trifocals and progressive lenses. Where a multifocal 
or progressive lens is produced, the preformed lens can be treated in 
accordance with the invention to provide an optical segment providing a 
second lens correction (e.g., bifocal), a third lens correction (e.g., 
trifocal), etc., each of which is different from the distance lens 
correction of the preformed lens (i.e., at its optical center). In such 
embodiments the mold is fashioned to correspond to the desired shape of 
the multifocal or progressive region of the resulting lens and any carrier 
layer, if used. The disclosed methods can also be used to change the power 
on portions of the preformed lens, to create prism, and to produce 
multifocal or progressive lenses from preformed lenses. During the casting 
and curing process, the mold and preformed lens may be held together by, 
among other means, peripheral clamping around the extreme periphery of the 
preformed lens and the mold, a conventional optical gasket which holds the 
preformed lens and mold together, by the force provided by the weight of 
the preformed lens when it is placed on top of the mold, capillary 
attraction resulting from a very thin film of resin material between the 
mold and preformed lens (resulting from the compressive force the mold or 
preformed lens on the resin material), or a combination thereof. However, 
preferred embodiments of the present invention do not require use of a 
conventional optical gasket, thus allowing more versatile and flexible 
casting and making such methods significantly more economical than 
traditional casting methods which employ conventional optical gaskets. The 
ability to cast lenses without conventional optical gaskets further 
eliminates a restrictive element which limits the possibilities of lens 
construction due to the physical confines of the conventional optical 
gasket. 
In some of such embodiments, molding material is dispensed without the use 
of conventional optical gaskets into the mold and the preformed lens is 
placed on top of the resin and slight pressure is applied which presses 
molding material out of the mold until the surface of the lens is 
separated from the mold by a thin carrier layer of molding material. The 
mold and preformed lens are held together by capillary attraction of the 
resin layer, by weight and/or other means. Thus a thin carrier layer of 
material is cast over the surface of the preformed lens, in addition to a 
segment or other optic surface defined by the mold, without the use of a 
conventional optical gasket. If less resin material is used, such method 
can also be employed to cast a multifocal or progressive region without 
also casting a carrier. Alternatively, the mold can be lowered onto the 
preformed lens containing molding material to achieve a similar effect. 
The methods of the present invention differ from prior processes by the 
fact that compressive forces are employed to cast the thin layer of resin 
material. Furthermore, in the process of the present invention, the resin 
material contracts or shrinks as it cures such that the upper of the mold 
and the preformed lens is pulled down toward the lower. 
The methods of the present invention are useful with respect to any 
preformed "plastic" optical lens regardless of the manner in which such 
lens was formed. As used herein a "plastic" lens is one fashioned from 
optical quality resin materials. Such materials include without limitation 
mixtures containing allyl diglycol carbonates (such as "MasterCast 1" and 
"MasterCast 2" which are trademarks of Vision Sciences, Monrovia, Calif.; 
and "CR-39" which is a trademark of PPG Industries), allylic esters such 
as triallyl cyanurate, triallyl phosphate, triallyl citrate, diallyphenyl 
phosphonate, acrylic esters, acrylates, methyl, allyl and butyl 
methacrylates, polycarbonates, styrenics, lexan, polyesters including 
those formed of ethylene glycol maleate and other liquid monomer/polymer 
materials having high indices of refraction (such as HiRi which is a 
trademark of PPG Industries). Resin materials which are photosensitive 
(i.e., photochromatic) or pretinted can also be used in practicing the 
present invention. 
Any surface of a preformed lens (i.e., front, back or both) can be altered 
using the methods of the present invention. Convex or concave surfaces can 
be treated. Only portions of a surface can also be treated. 
For example, as shown in FIG. 1, the curvature of a lens surface 11 can be 
changed over a small area by providing an "optical segment" 12 which is 
substantially smaller than the preformed lens 11. Such optical segments 
most often serve to provide bifocal or trifocal vision, but can also be 
used for other purposes. 
In other embodiments, an entire surface of a lens can be altered in 
accordance with the methods of the present invention for the purpose of, 
for example, converting the preformed lens into a progressive lens, 
providing, for example, a seamless multifocal, bifocal or trifocal lens or 
inducing prismatic effects in the finished lens. In such embodiments, in 
addition to a segment if desired, as shown in FIG. 2, the surface of the 
preformed lens is recast with an additional non-prescription carrier layer 
of resin material to produce the desired lens design without changing the 
prescription or correction at the optical center of the finished lens. 
Preferably, the additional carrier layer is very thin (preferably 
0.025-0.5 mm) to promote rapid curing and decrease the probability of 
developing stress and distortion in the resulting finished lens. 
Although optical segments can be placed in any location on the lens, for 
normal applications, the optical segment should be properly located to 
avoid adverse prismatic effects. Optimally, an optical segment should be 
positioned approximately 1.5 mm left or right and 3-5 mm down from the 
optical center of the lens for normal eyeglasses. In certain applications, 
such as workman's glasses for close vision above the wearer's head, the 
optical segment can be optimally located approximately 1.5 mm left or 
right and 3-5 mm above the optical center of the lens. Other locations of 
the optical segment can also be used as long as the optical center and the 
segment are properly aligned. 
The methods of the present invention can also be for properly orienting the 
optical center of the lens with respect to the multifocal or progressive 
region. Also they can be used to cast compensating base-down prism in 
conjunction with casting a progressive lens. Appropriate lens designs 
providing prismatic effects will be apparent to those skilled in the art. 
Where creating prism is desired, the casting mold is configured and 
positioned with respect to the preformed lens to provide the required 
additional thickness in the resulting lens. The mold and the preformed 
lens may be properly oriented by spacers which provide the desired 
separation, corresponding to the required thickness for inducing the 
prismatic effects sought. Such spacers can take any form, including 
wedges, and can be fashioned from any suitable material. The spacers can 
be incorporated into a conventional optical gasket, if one is used, or 
formed on the surface of the mold or preform. Other means for orienting 
the mold and preformed lens to induce prismatic effects will be apparent 
to skilled artisans. 
The optical center can be moved or displaced, as shown in FIG. 7, by 
physically moving the optical center 25 of preformed lens 11 to align with 
the desired location just above the edge of the multifocal region in the 
case of a multifocal lens or to the proper mold position in the case of a 
progressive lens, then casting the new lens surface. Since some methods of 
the present invention do not employ a conventional optical gasket, such 
dislocation of the preformed lens with respect to the mold is possible. 
Conventional methods employing a conventional optical gasket make such 
dislocation virtually impossible because the conventional optical gasket 
will not allow movement of the lens with respect to the mold. It should 
also be noted that, when dislocating the preformed lens in relation to the 
mold size as just described, more useful lens area can be produced by 
increasing the size of the preformed lens such that more of the surface of 
the mold contacts the preformed lens, thus producing a larger finished 
lens surface. However, either the preformed lens or the mold can be the 
larger in size to achieve the desired displacement or decentration, or the 
preformed lens and the mold can be the same size and simply moved relative 
to each other. 
In some lens designs adjustments must be made to accommodate astigmatism in 
the prescription of the finished resulting lens. In such cases, the 
preformed lens and mold must be rotated with respect to each other to a 
degree corresponding to the proper astigmatic axis. The preformed lens and 
mold can either be contacted at the proper angle or can be rotated with 
respect to each other after contact. The mold, preformed lens or 
conventional optical gasket (if used) can optionally be provided with 
appropriate markings (e.g., protractor lines) for determining the proper 
astigmatic axis. Alternatively, the mold and preformed lens can be 
assembled within or on a circular protractor which serves to align the 
astigmatic axis and to hold the assembly in place. 
In multifocal lenses it is important to properly orient the optical center, 
the multifocal region and the astigmatic axis of the finished lens with 
respect to each other. This can be achieved, for example as shown in FIG. 
7, by combining the methods described above for inducing prismatic effects 
and for aligning the astigmatic axis. 
Generally, the preformed lens is transformed by casting a layer of optical 
quality resin material on at least a portion of the preformed lens 
surface. As shown in the Figures, the contours of the casting are 
determined by mold 13. Mold 13 is shaped such that the cavity 14 formed 
between lens 11 and mold 13 corresponds to the desired change in curvature 
of the lens, including the multifocal or progressive region (e.g., optical 
segment 12) and non-prescription carrier layer 16, if used. For example as 
shown in FIG. 1, mold 13 is fashioned such that cavity 14 defines an 
optical segment 12 at the desired location and of the desired thickness 
and shape to provide a desired lens design. In FIG. 2, cavity 14 defines 
an optical segment 12 and non-prescription carrier 16. Similarly, as shown 
in FIG. 9, mold 13 can be fashioned such that the cavity 14 defines new 
structure on the back surface of the preformed lens 11 such that the 
surface is changed to provide the desired lens design. 
Molds can be made from any material which will provide an optical quality 
surface when used for casting, such as Crown glass or electroformed 
nickel. Means for making appropriate molds and for fashioning such molds 
for use in accordance with the present invention are known in the art. 
To cast the new lens surface, an optical resin monomer material is 
dispensed onto the preformed lens, onto the mold or into the cavity, and 
then cured. In certain embodiments only a portion of cavity may be filled 
with material to form the desired new surface. Appropriate optical resin 
materials include those previously discussed among others. Certain 
materials used to "hardcoat" lenses (such as those described in U.S. Pat. 
Nos. 4,758,448 and 4,544,572, which are incorporated herein by reference) 
can also be used as the resin material, thus providing a durable surface 
to the portions of the finished lens cast in accordance with the present 
invention. Hard coat materials can also be blended with other resins for 
use in practicing the present invention. Furthermore, the resultant lens 
can be a composite of high index plastic materials and more scratch 
resistant materials. The resin material should, however, be chosen such 
that upon curing the material will both harden and bond with the material 
of the preformed surface of the lens. Preferably the resin material will 
form what is thought to be intermolecular bonds with the material of the 
preformed lens. 
In preferred embodiments, both the preformed lens and the resin material 
used to recast the lens surface are the same or similar material. Use of 
the same or similar materials prevents separation or "crazing" (i.e., 
cracking) of the new surface from the preformed lens as a result of 
different expansion/contraction rates for the preformed lens and recasting 
materials. Applicant also believes that use of the same or similar 
materials may allow formation of intermolecular bonds between the new 
resin and the surface of the preformed lens. 
The resin material composition may also contain various additives which 
will alter the resulting lens including without limitation tints, 
antireflection coatings, antiscratch coatings, and ultraviolet inhibitors. 
The resulting lens may also be subjected to treatments frequently applied 
to plastic lenses, including without limitation tinting and coating with 
ultraviolet inhibitors and antireflection and antiscratch coatings, 
according to known methods. 
Coatings can also be provided to the resultant lens by transferring 
coatings from the mold to the resultant lens. In such embodiments, the 
mold is first coated with the material to be transferee to the lens, such 
as antiscratch, antireflective, photosensitive or hard coatings. The 
coated mold is then employed as described herein. If the coating material 
has a greater affinity for the lens resin material than for the mold 
surface, the coating will be transferee to the surface of the resultant 
lens. Suitable materials and means for applying them are known in the art, 
including without limitation those disclosed in U.S. Pat. Nos. 4,758,448 
and 4,544,572. 
Ultraviolet curing allows use of tinting agents in the resin composition 
which would be decomposed or volatilized during thermal curing processes. 
If UV curing is used, in most cases, tinting agents can be added to the 
resin composition before curing and incorporated relatively uniformly into 
the resulting finished lens. Since in some cases significant heat does not 
need to be employed in the UV curing process the tinting agent is retained 
by the resin material during the curing process. This is accomplished 
because no peroxide-based thermal initiator is used therein. 
In certain embodiments, as shown in FIG. 3 for example, the preformed lens 
is masked with tape 15 or other appropriate materials. The masking can be 
used on the side of lens which is to be cast in accordance with the 
present invention, thus preventing casting undesired portions of the lens 
surface. Alternatively, the mask can be applied to the opposite surface of 
the lens to limit the area through which UV radiation can reach the resin 
material, thus limiting the area in which the resin is cured. Masks can 
also be used on the mold, the preformed lens, or both, and on both sides 
of each and any component. 
However, tinting lenses having an optical segment cured using UV can 
present certain problems. When such lenses are soaked in the tinting bath, 
the optical segment may get darker than desired due to the softer 
consistency of the segment caused by uneven curing as a result of its 
variable thickness. These problems can be avoided in several ways. First, 
the preformed lens could be pre-tinted and then cast in accordance with 
the present invention. Since tint need not be applied to the optical 
segment in such embodiments the tinting problem is avoided while the tint 
effect is still observed over the entire surface of the lens. Second, the 
resultant lens could be masked on its front surface (including the optical 
segment) before tinting. Thus, the tint is only absorbed into the back 
surface of the lens and not into the optical segment. Preferably the 
tinting mask is transparent to allow monitoring of the tinting process. 
The preformed lens and mold may be separated by spacers which maintain a 
desired separation between the lens and the mold, thus providing a recast 
surface of a desired thickness. Spacers can be incorporated as part of a 
conventional optical gasket used to hold the lens and mold together or can 
be used independent of a conventional optical gasket. Any suitable 
material, for example, small pieces of tape can be located between the 
lens and mold at various points around the periphery of the lens/mold 
assembly as shown in FIG. 10. Using carpet tape provides a surface 
approximately 0.4 mm thick, while use of (commercially-available 
transparent adhesive tape (e.g., "SCOTCH" brand tape) provides a surface 
0.2-0.3 mm thick. Spacers can also be constructed from material that is 
the same as or similar to the preformed lens and/or the resin composition. 
Upon curing, such a spacer could become incorporated into the finished 
resulting lens. Finally, spacers can be a part of the mold or preformed 
lens (e.g., raised bumps on the surface which provide the desired 
separation). In certain embodiments, spacers are not used and the 
preformed lens and mold are either not separated or are separated by a 
thin carrier layer of resin composition formed by capillary action when 
the preformed lens and mold are contacted. Such layers cast in accordance 
with the present invention have been measured as thin as 0.025-0.05 mm 
thick. In most cases, such methods do not employ a conventional optical 
gasket. 
In certain embodiments, the resin is not dispensed into the cavity until 
after the mold and preformed lens are assembled. In such embodiments the 
resin material is injected into the resulting cavity through a channel in 
the mold, conventional optical gasket or preformed lens, taking care to 
prevent formation of air pockets within the cavity. Any burrs or other 
artifacts resulting from the presence of such a channel or other structure 
can then be removed during finishing of the resulting lens. 
Once the mold and the preformed lens are assembled the resin material in 
the resulting cavity must be cured to harden and bond with the preformed 
lens surface. The resin material may be cured in any manner appropriate to 
the composition of such material. Most materials can be cured by exposure 
to heat or ultraviolet radiation ("UV"). Other curing methods may include 
without limitation ultrasound, infrared, microwave and other forms of 
radiation. Thermal initiators (such as diisopropyl peroxydicarbonate) 
and/or UV initiators (such as 2-hydroxy-2-methyl-1-phenyl-propan-1-one or 
1-hydroxycyclohexylphenyl ketone) are mixed with the optical resin 
material before it is used. 
Suitable UV light sources include those manufactured by Phillips 
Corporation and identified as TL/10R/UVA reflector lamps, HPM high 
pressure halide lamps, HPA medium pressure metal halide lamps and HPR high 
pressure mercury vapor lamps. In preferred embodiments, the UV source 
(300-450 nm) is applied during the curing process until the resin hardens 
sufficiently (approximately 5-30 minutes). In some cases, the lenses to be 
cured are placed onto a turntable for rotating the lenses through the 
stream of incident radiation in order to achieve more even curing and 
maximizing the number of lenses which can be cast within a given area. 
Other appropriate UV light sources and conditions for exposure will depend 
upon the resin composition employed and will be apparent to those skilled 
in the art. 
Curing can also be performed using a "blinking" UV light source. Curing 
with a blinking source tends to produce an optical segment with less 
variation in consistency. 
Heat or UV, or both, may be applied by any means appropriate to the 
material from which the mold and preformed lens are made. Unlike thermal 
curing, UV curing requires at least one UV transparent surface through 
which the UV radiation can travel to reach the resin monomer material. 
Although the preformed lens provides one transparent surface, forming the 
mold from a UV-transmitting material will provide additional transparent 
surfaces and will promote faster, more even curing. Upon application of 
heat, UV or both, the initiators cause the optical resin material to 
polymerize and to bond to the surface of the preformed lens. 
Certain embodiments of the present invention use a reflective surface on 
the surface of the mold to reflect ultraviolet light back through the lens 
resin material being cured. The mold includes a reflective surface 
conformed to the casting surface of the mold. The exposed surface of the 
reflective surface is highly polished to reflect ultraviolet light rays 
from ultraviolet light source. This surface of the reflective surface may 
act directly as a casting surface that produces an optical quality lens 
surface or may be fixed beneath a transparent layer which acts as the 
actual casting surface of the mold. 
Some materials can be cured by a combination of heat and UV applied 
sequentially or simultaneously. For example, applicant's co-pending 
application Ser. No. 190,856, filed May 6, 1988, and now U.S. Pat. No. 
4,919,850, which is incorporated herein by reference, discloses a resin 
material and means for curing such material using both heat and UV. Such 
material includes a liquid monomer, a thermal initiator, plus a 
photosensitive ultraviolet initiator. In this process, the liquid monomer 
lens resin material is placed into the desired preformed lens/mold 
combination and subjected to thermal curing using a heated fluid bath 
(preferably 150.degree.-180.degree. F.) for a short period of time, less 
than ten (10) minutes. The heat activates the thermal initiator and forms 
the lens material mixture into a gel which freezes the photosensitive 
initiator in place throughout the lens material. Furthermore, this gelled 
state preestablishes the optical framework needed for an optical lens 
relatively free of optical distortion or imperfections. After the lens 
material mixture has sufficiently gelled, it is then subjected to 
ultraviolet light to activate the photosensitive initiator and complete 
the polymerization or curing process to form the finished lens. 
Preferred resin compositions for use with such a combined thermal/UV curing 
process comprises resin monomer (such as CR-39), 0.5-5.0% by weight 
thermal initiator (such as diisopropyl peroxydicarbonate), and 1-8% by 
volume photosensitive initiator (such as 
2-hydroxy-2-methyl-phenyl-propan-1-one or 1-hydroxycyclohexylphenyl 
ketone, which are sensitive to ultraviolet light). 
Particularly for lens manufacturing processes using UV curing, a yellow 
tint may remain in the resulting lens or may evolve during aging. This 
tinting or "yellowing" can be reduced by curing the lens material with the 
addition of certain anti-yellowing chemical agents. These include amine 
hindered amine light stabilizer (HALS); optical brighteners which makes 
the yellowing or hindered phenol antioxidants. Another method is to use a 
photosensitive initiator which is not from the amine group and which will 
not cause yellowing. 
It has also been found that inadvertent post curing and additional 
yellowing or discoloration can occur after a lens has been cured by 
permitting the lens to be subjected to a UV curing process longer than 
desired or inadvertently exposing the lenses to sunlight or artificial 
light, which includes wavelengths of the UV spectrum, during processing or 
use. Additional exposure to UV light produces a continued curing effect 
because of the remaining UV initiator in the formed plastic lens. This can 
cause the lens to be unduly brittle and cosmetically discolored, 
permitting it to be readily fractured and detracting from the normal life 
or commercial sale of the lens. 
The invention described herein can include the use of UV inhibitors coated 
on the surface of the cured lens or absorbed into the surface of the cured 
lens to avoid any additional effect on the UV initiators and to 
substantially prevent or entirely eliminate the transmission of UV light 
waves into the lens. Such processes are further described in co-pending 
U.S. patent application Ser. No. 339,217, filed Apr. 17, 1989, and now 
U.S. Pat. No. 5,028,538. This coating can take the form of anti-reflective 
coating, a scratch-resistant coating, any tinting coatings, or simple 
wavelength coating which could be basically clear for preventing UV 
wavelengths from being transmitted. Such UV inhibitors are well known in 
the art and need not be described in detail herein. It is desirable to 
have the UV inhibitor eliminate all UV light and other wavelengths having 
a wavelength of 500 nm or less and more specifically between 300-425 nm. 
This treatment process normally involves, after the curing steps, simply 
dipping the cured lenses into a hot bath having any one of the coatings 
mentioned above to coat the surfaces sufficiently such that the entire 
surface of the lens is covered with the inhibitor. This dipping process, 
as well as other processes for applying the coatings noted above are well 
known to those skilled in the art. The UV inhibitor can be used in 
solution or otherwise form a composition with the coatings discussed 
above, such that the desired coating along with the inhibitor can be 
applied to the lens in a one step process. Some inhibitor may be absorbed 
into the lens material. Other known methods of coating can be used in 
applying the UV inhibitor in the manner described above. 
Prior to lens surface treatment, if any additional hardening is required, 
the lens can be subjected to "post curing". Although a post cure can be 
utilized with any of the above noted processes, it is not normally used 
for bath cures since the mold and other intervening media may affect the 
ability to achieve maximum hardness. Preferably for post curing, after the 
thermal and/or UV cure, the lens is separated from the mold and subjected 
directly to UV or heat. This post cure using UV and or a thermal source 
will harden the lens material even further should such additional hardness 
be required. In some cases, post curing with UV is done with a filter mask 
that allows more UV radiation to strike the thicker surfaces of the lens. 
Applying an optical segment in accordance with the present invention may in 
some instances produce a minor, but beneficial transition in the finished 
lens near the edge of the segment. This phenomenon has been observed 
mainly in connection with the formation of multifocal segments having a 
flat edge. For example, as shown in FIG. 6, when applying a conventional 
flat top 28 +250 bifocal segment to a plano preformed lens, the main 
prescription of the segment may be +250 while the upper edge of the 
segment may be only +212. The optical center of the preformed lens may 
remain plano, but the area of the lens just above the segment may be, for 
example, +87. This beneficial transition provides a possible effect in 
that when the wearer's eye moves from the main prescription to the bifocal 
prescription the eye is eased from lower to higher power, thus requiring a 
less drastic change in accommodation. 
In effect, a bifocal lens having such a transition provides at least four 
different lens corrections or prescriptions at different regions of the 
lens. As shown in FIG. 6, the lens has a first correction in the region 17 
of its optical center and a second lens correction in a second region 18 
at the center of the bifocal segment. The geometric center of the lens is 
indicated at 30. A third lens correction is provided by a third region 19 
located adjacent to the edge of the segment (i.e., adjacent to the second 
region) approximately along an imaginary line (indicated by a dotted line) 
extending from the geometric center of the segment to the optical center 
of the lens. A fourth lens correction is provided by a fourth region 20 
located within the segment (i.e., within the second region) and 
approximately along the same imaginary line. The magnitude of the third 
lens correction is between the magnitudes of the first and fourth lens 
corrections and the magnitude of the fourth lens correction is between the 
magnitudes of the second and third lens corrections. For example, in the 
example previously discussed the first, second, third and fourth lens 
corrections are plano, +250, +87 and +212, respectively. In other 
multifocal lenses additional lens corrections may also be provided by the 
segment. 
However, in many instances such transition is undesirable and can be 
prevented or alleviated in several ways. At present, applicants believes 
that the transition is caused by uneven curing of the segment and the thin 
carrier layer which are cast on the surface of the preformed lens. Due to 
the different thicknesses of portions of the newly applied surface, curing 
occurs at different rates and to different degrees during exposure to UV 
light or other curing methods. This results in areas of the lens which are 
harder than others and may result in uneven shrinkage and stress of 
different lens portions, thus producing the transition. Therefore, any 
means for promoting even curing of the newly cast surface will serve to 
prevent or alleviate the transition. 
For example, the preformed lens could be provided with a mask which 
selectively transmits UV light at different levels. Thicker portions of 
the cast surface are covered with a mask transmitting more light, while 
thinner portions of the cast surface are covered with a mask transmitting 
significantly less light. In the case previously described for the 
addition of a +250 bifocal segment, for example, the portion of the mask 
covering the thickest upper edge of the segment would transmit 100% of 
incident UV light, that covering the rest of the segment would be 
gradually decreased over a spectrum until the thinnest portion of segment 
received only 55% of the incident light, and that covering the rest of the 
surface of the preformed lens would transmit 50%. 
Another means for achieving more even curing of the segment and thin layer 
employs a shutter or aperture in association with the UV light source 
which is opened and closed such that thicker areas of the recast surface 
are exposed to more light than thinner surfaces. This can be accomplished 
by either exposing the entire surface to light and then gradually closing 
the aperture to expose only the thicker portions of the surface, or by 
exposing only the thicker portions of the surface and then gradually 
opening the aperture to expose more of the surface until the entire 
surface is exposed. 
The transition can also be avoided, reduced or removed by modifying the 
casting procedure in several ways, among others. First, casting carrier 
layers thicker than 0.8 mm decreases the likelihood of the distortion 
occurring. Second, the optical segment can be cast in multiple layers of 
lesser thickness. For example, as shown in FIGS. 4 and 5, the preformed 
lens 11 can be cast with a carrier 16 and a segment 21 of one-half the 
final desired power. This lens is then cast again, as shown in FIG. 5, 
with an additional carrier layer 22 with a mold 23 corresponding to the 
full desired thickness of the final segment 12, resulting in a finished 
lens having the desired optical segment. Third, the desired segment can be 
cast, cured and then recast with an additional layer using a mold of the 
same shape, for example as shown in FIG. 11. Such layer can be a thin film 
(e.g., 0.025-0.05 mm) or can be a thicker layer if spacers are used. 
Recasting fills in any transitions, distortions or defects which may have 
arisen during the first casting. Since the recast layer is a very thin 
film of resin material, it is not as susceptible to transition or other 
aberration. Approximately 90% of lenses having the distortion were found 
to be corrected by recasting the surface of the lens with a layer at least 
approximately 0.2 mm thick. Recasting may also be repeated again and again 
until the desired quality of surface is achieved seeing as almost no 
resulting thickness is added to the lens with each recasting. The 
resulting surface is then free of this type of transition. Fourth, the 
transition can also be avoided or diminished by forming an optical segment 
with a thinner edge than a flat top segment. For example, a curved top or 
round segment can be used. Fifth, reducing incident UV radiation while 
extending UV curing time can also reduce this effect. Sixth, the 
transition can be avoided or diminished by providing a mold which 
accommodates for the transition by providing excess resin material which 
will shrink unevenly to reach the desired transition shape. Finally, the 
distortion can be reduced by employing a resin material which has a low 
shrink rate. 
The recasting method can also be used to correct other defects in rejected 
or damaged cast lenses. A defective lens can be recast with a thin 
non-prescription film layer using a mold of the same shape to remove the 
defects, thus decreasing yield losses during the manufacturing process. 
Recastings according to this method can be cured in any appropriate manner 
in far less time than the initial casting due to the thin film layer to be 
cured. Furthermore, significant savings can be accomplished due to use of 
less resin material and, in most cases, elimination of the need for a 
conventional optical gasket. 
A preformed lens can also be combined according to the present invention 
with a second preform providing a multifocal or progressive region. As 
shown in FIG. 8, second preform 26 provides a multifocal region 27. Second 
preform 26 and preformed lens 11 are contacted to form a cavity 28 
corresponding to a thin carrier layer 29 of resin material. Curing of the 
resin bonds second preform 26 to preformed lens 11. Preferably, the second 
preform, preformed lens and resin material are of the same material, 
although different materials may be used. A conventional optical gasket or 
mold may optionally be used to help hold the second preform and preformed 
lens in proper orientation and to provide the desired thickness to the 
carrier layer. 
Separation of molds from the resultant lens can be facilitated by putting 
the assembled apparatus on ice or in some other cold source (e.g., a 
compressed cooling gas, such as "FREON"). The exposure to cold causes the 
resultant lens and molds to contract and pull away from each other such 
that the components can be more easily separated. Although more 
traditional separation methods using a water bath can be used, the 
separation with a cold source eliminates the need to remove water from the 
resultant lens and molds before further operations can be performed. 
While employing the methods of the present invention in casting lenses, the 
resultant lenses can be marked with various "unseen" markings by employing 
molds which have minor imperfections corresponding to these markings when 
curing with UV light. When a mold contains an imperfection, the 
imperfection refracts the UV light such that exposure of the resin to the 
light source becomes uneven. The uneven curing causes a harmless 
distortion in the resultant lens which correspond to the imperfection in 
the lens, thus creating the marking. In many instances these markings will 
be invisible to the naked eye and can only be seen by using a polariscope. 
For example, a mold could be embossed with numbers corresponding to the 
prescription cast thereby such that the resulting lens is marked with the 
prescription when viewed under a polariscope. These markings could also be 
employed to mark features of the lens including without limitation the 
astigmatic axis, optical center, base curve, right, left, progressive 
region, optical segment and mold number. 
Certain embodiments of the present invention are demonstrated by the 
following examples which are intended as illustrations and not as limiting 
the invention in any way. 
EXAMPLE 1 
A mold was fashioned to define the contours of an optical segment which was 
to provide a bifocal. The mold was made from Crown glass, electroformed 
nickel, or other material having the ability to cast an optical quality 
surface. 
An optical resin material was then prepared consisting of MasterCast 1 or 2 
(which contain a thermal initiator) and an added UV initiator 
(2-hydroxy-2-methyl-phenyl-propan-1-one, 6.5% by volume). The resin 
mixture was then dispensed into the mold. The front surface of a preformed 
lens (made from MasterCast 1 or 2) was masked with tape to cover all of 
such front surface except for the area where optical segment 12 was to be 
attached. The mask prevented resin from depositing on the lens surface in 
undesired locations and acts to block or channel UV radiation only to the 
area to be cured. The mold and the masked preformed lens were then 
contacted to form a cavity corresponding to the configuration of the 
optical segment. The preformed lens was placed on top of the mold filled 
with resin material and slight pressure was applied to squeeze out excess 
resin material. The weight of the preformed lens and capillary action of 
the resin material were sufficient to hold the assembly together without 
use of a conventional optical gasket. 
The resin material was then cured using UV light (300-450 nm) until the 
resin hardened sufficiently (approximately 10-20 minutes) using a UV light 
source manufactured by Phillips Corporation and identified as a TL/10R/UVA 
reflector lamp. The mold and preformed lens were then separated. The 
finished lens was then edged, finished and mounted. 
EXAMPLE 2 
A lens was made as described in Example 1 with the exception that the resin 
material was cured using a combination of heat and UV radiation. The 
preformed lens/mold assembly containing the monomer resin material was 
placed in a water bath at approximately 180.degree. F. until the resin 
material gelled (approximately 10-15 minutes) The assembly was then 
exposed to UV as described in Example 1 for 10-20 minutes to complete 
curing. The resulting lens was then edged, finished and mounted. 
EXAMPLE 3 
A lens was made and cured as described in Example 1, with the exception 
that the resin material comprised MasterCast 1 or 2 (without a thermal 
initiator) and the same UV initiator, and the preformed lens was not 
masked. 
EXAMPLE 4 
A lens was made to provide a multifocal optical surface and to induce 
appropriate prismatic effects. The lens was made and cured, as described 
in Example 3, with the exception that the conventional optical gasket used 
to hold the preformed lens and mold together was fashioned to separate 
edges of the preformed lens and mold to provide the necessary additional 
thickness in the resulting lens to provide the desired prismatic effect. 
Alternatively, a wedge of appropriate thickness was placed between the 
edge of the preformed lens and the mold to provide the required 
separation. 
EXAMPLE 5 
A lens was made as described in Example 3. The assembled mold and lens were 
then placed in a plastic or rubber conventional optical gasket which 
surrounded the periphery of the assembly and held the assembly together. 
The conventional optical gasket was fashioned such that the lens and mold 
were separated by a thin space which allowed the formation of a thin layer 
of resin over the entire surface of the preformed lens. The lens 
correction at the optic center of the resulting lens was the same as that 
of the preformed lens. 
EXAMPLE 6 
A lens was made as described in Example 3. Three squares of transparent 
tape (approximately 1-2 mm wide) were evenly spaced around the outer edge 
of the front surface of the preformed lens. The squares acted as spacers 
to produce, upon casting, a thin nonprescription carrier layer 
(approximately 0.2 mm thick) over the surface of the preformed lens. 
EXAMPLE 7 
A lens was cast by physically relocating the optical center of the 
preformed lens to be properly aligned with the optical segment of the 
finished lens. A mold defining an optical segment was filled with a 
portion of resin composition. A preformed lens was provided which had a 
diameter significantly larger than the diameter of the mold. To cast the 
finished lens, the optical center of the preformed lens was marked and was 
then positioned ("relocated") in proper alignment with the portion of the 
mold corresponding to the optical segment. When aligned, due to its larger 
diameter, the preformed lens still covered the entire mold, while a 
portion of the preformed lens extended beyond the mold. The preformed lens 
was then lightly pressed against the mold and excess resin was severed out 
of the resultant cavity. No conventional optical gasket was used and the 
preformed lens/mold assembly was held together by capillary action of the 
resin material. After curing, the cast lens was separated from the mold. 
That portion of the preformed lens which extended beyond the mold (and was 
not cast with new resin) was then cut away to leave the useful 
prescription lens surface for further finishing. 
EXAMPLE 8 
A lens was made as described in Example 3 to provide a flat top 28 +250 
optical segment. The resultant finished lens was observed to contain a 
minor beneficial distortion as previously 
described. This "distorted" lens was then used as a preformed lens and was 
cast again using the same mold according to the same method. The resulting 
lens was observed to be virtually free of the previously observed 
distortion. 
EXAMPLE 9 
A lens was made as described in Example 3, except that the preformed lens 
was made from a high index plastic (HiRi), a material different from the 
carrier layer and optical segment casting resin material (MasterCast 1 or 
2 which contains CR-39), is softer and has a different index of 
refraction. The cast layer bonded to the surface of the preformed lens and 
provided an optical quality product. 
The above has been a detailed discussion of certain embodiments of the 
present invention. They should not be considered so as to limit the scope 
of applicant's invention which is defined by the appended claims.