Method of manufacturing a contact lens

Methods of manufacturing a contact lens form a mold which has a first section formed from a first material and a second section formed from a second material. The methods permit the facile preparation of contact lenses having two or more differing materials, for example, a composite lens, a bifocal lens, a trifocal lens and the like.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a method of manufacturing a contact lens, and, in 
particular, to a method of manufacturing a contact lens from two or more 
differing materials, for example a composite lens, bifocal or trifocal 
lens. 
2. State of the Art 
Normally contact lenses when formed from two or more materials are formed 
with a first member formed from a first material, and a second member 
formed from a second material. One particular example of this is a 
composite lens which is generically known as "Saturn" in the industry 
wherein the first member comprises the optical zone of the lenses and is 
normally made from a "hard" material such as a rigid gas permeable (RGP) 
material, and the second member comprises a skirt around the optical zone 
and is normally made from a "soft" material, such as a hydrogel material. 
At present composite lenses of the general type described above are 
manufactured from buttons that are formed by the following process steps: 
forming a first rod of material by polymerisation of a first monomer 
material; 
forming a layer of a second material about said first rod of material by 
polymerisation and 
transversely slicing the rod so formed into buttons. 
The problems associated with the above mentioned manufacturing technique 
for the button include: 
the fact that the first rod of material must be located centrally within 
the finished buttons. With the procedures employed in the industry this is 
not so easily achieved, and consequently there is considerable scope for 
error from this aspect, leading to a high rejection level of rods and 
buttons; 
the actual diameter of the first rod of material provides the dimensions of 
a significant characteristic of the finished lens. Therefore the first rod 
of material has to have a uniform diameter; and 
the adhesion between the two materials of the two members as a result of 
the different character of the materials of the composite lens may be very 
low, and when this is combined with the fact that the soft contact lens 
material will be swollen after manufacture and prior to use exerting a 
considerable force on this adhesion the problems can be significant. 
The net result of the above is that the production of composite contact 
lens using buttons in accordance with the above detailed method is 
expensive, with a high rejection of rods, buttons and lens. 
Above the situations and problems have been discussed with regard to one 
particular example, namely a "Saturn" lens, it should however be noted 
that the situation and problems ape very similar to those that would be 
encountered for the production of bifocal and other multifocal lenses from 
two of mope different polymeric materials. 
SUMMARY OF THE INVENTION 
The present invention is concerned with providing a method of manufacturing 
contact lenses for example composite contact lenses of multifocal contact 
lenses in which the above discussed problems have at least been alleviated 
of reduced significantly. 
In accordance with the present invention in its broadest scope, there is 
disclosed a method of manufacturing a contact lens which has a first 
section formed from a first material, and a second section formed from a 
second material which method includes the use of a casting mould of 
generally cylindrical construction and having a side wall and an end wall, 
which end wall has an inward displacement into the space defined by the 
side wall, which space defined by the side wall and end wall is a 
receptive well into which material can be cast to be cured/polymerised, 
which method comprises 
casting a first monomer material into the receptive well of the casting 
mold, and polymerising/curing the monomer material; and 
machining the article formed by the above casting into a contact lens 
wherein the first monomer material includes a polymerisable material which 
has a penetrating like action with respect to the material from which the 
end wall of the casting mould is formed. 
The casting moulds for use in the method of manufacture of the present 
invention, can be mass produced from suitable contact lens materials 
relatively cheaply and with a high degree of accuracy. For example the 
moulds may be produced by moulding of the material in a polystyrene mould. 
The polystyrene mould itself being injection moulded at a very low cost. 
From this it will be readily understood by those in the industry that 
contact lenses which are made from two or more different materials can be 
made by the method in accordance with the present invention cheaply and 
easily, as the problems of the currently known process are significantly 
alleviated if not eliminated altogether. 
In one arrangement of the present invention the inward displacement of the 
end wall of the casting mould is a solid projection the material of which 
forms one of the sections of the contact lens. 
Alternatively, the inward displacement of the end wall of the casting mould 
may define a second receptive well into which a second monomer material 
may be cast, and subsequently polymerised/cured prior to machining. In 
accordance with a second aspect of the present invention a method of 
manufacturing a contact lens which has a first section formed from a first 
material, and a second section formed from a second material, includes the 
use of a casting mould of cylindrical construction and having a side wall 
and an end wall, which end wall has an inward displacement into a space 
defined by the side wall so that the casting mould has two receptive wells 
for the casting of material to be cured/polymerised which are separated 
from one another by the end wall of the casting mould, which method 
comprises: 
casting a first monomer material into one of the receptive wells of the 
casting mould, and polymerising/curing the monomer material; 
casting a second monomer material into the other receptive well of the 
casting mould, and, polymerising/curing the monomer material; and 
machining the article formed by the above castings into a contact lens 
wherein the first and second monomer materials include a polymerisable 
material which has a penetrating like action with respect to the material 
from which the end wall of the casting mould is formed. 
The inclusion in the first and second monomer materials of a polymerisable 
material with a penetrating like action with respect to the material of 
the end wall of the casting mould means that the polymerisable material 
softens, swells and/or dissolves the surface material of the end wall of 
the casting mould and upon polymerisation a very strong bonded interface 
is produced between the monomer material cast and the end wall of the 
casting mould. In fact the bond strength of a button made in accordance 
with the present invention is significantly increased over that which 
would be present should the two materials have been placed in direct 
contact bonding. 
When both of the casting operations have been completed a button is formed 
which includes the end wall of the casting mould sandwiched between the 
two bodies of polymerised first and second monomer material, each of the 
bodies of polymerised first and second monomer material being strongly 
bonded to the respective surface of the end wall of the casting mould as 
discussed in the paragraph above. 
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The incorporation of the casting mould, or a part thereof, into the button 
means that the method in accordance with the present invention utilises a 
simple one or two stage cast moulding operation which is significantly 
cheaper to operate than the presently used method. 
The accuracy of the alignment of the two materials, centre and skirt, is 
easily achieved by accurate manufacture of the casting mould, for example, 
by injection moulding. Consequently centration is ensured by the mould. In 
a preferred embodiment of the present invention the casting mould is 
formed with a side wall and end wall that are formed from the same 
material, so a strong interface is also formed between the cast material 
and the side wall. 
Preferably, the end wall has an inward displacement into the space defined 
by the side wall of the casting mould which inward displacement is conical 
in shape. 
The cone so formed as the inward displacement may have a base area which is 
any proportion of the area of the end wall of the mould up to 100%. 
Further the cone may be located with its apex at the, or in line with the, 
centre of the end wall or off centre therefrom. 
Alternatively, the inward displacement in the end wall of the mould may 
comprise an upstanding cylinder. The upstanding cylinder may be of any 
suitable cross-sectional shape, for example, circular, oval, semi-circular 
or polygonal. 
From the above it will be clearly apparent to anyone skilled in the 
industry that the method in accordance with the present invention can be 
used to manufacture contact lenses which have a member (or members). 
The use of a casting mould having an inward displacement means that the two 
receptive wells of the casting mould are defined as follows 
one receptive well which is defined by the inward displacement in the end 
wall of the casting mould only; and 
one receptive well which is defined by the side wall and the end wall. 
In one particular arrangement of the present invention the end wall of the 
casting mould, at least, is formed from polymethylmethacrylate and the 
polymerisable material with a penetrating like action of the first and 
second monomer materials is methylmethacrylate. 
As will be well appreciated by those skilled in the art there is a close 
relationship between the choice of the mould material and the 
polymerisable material with a penetrating like action, and the example 
given above is only that and is not to be construed as limiting on the 
invention as disclosed. 
As a general point liquid vinyl polymers and their monomers are useable in 
the present invention, for example, styrene, N-vinyl pyrrolidone (NVP), 
hydroxyethylmethacrylate (HEMA), dimethyl acrylamide (DMA), 
ethyleneglycoldimethacrylate (EGDMA), glyceral methacrylate (GMA). 
In a first specific alternative of this arrangement of the present 
invention the end wall of the casting mould, at least, is formed from 
cellulose acetate butyrate (Eastman Kodak TENITE M6 350A), resin and 
plasticiser, with the polymerisable material with the penetrating like 
action of the first and second monomer materials being a liquid vinyl 
monomer such as methyl methacrylate. 
In a second alternative to the first arrangement of the present invention 
the end wall of the casting mould, at least, is formed from polystyrene 
with the polymerisable material with penetrating like action of the first 
and second monomer materials being a liquid vinyl monomer such as N-vinyl 
pyrrolidone. 
In one particular arrangement of the present invention the end walls of the 
casting moulds, at least, are coloured. The colouring of the casting mould 
end wall, means that when the finished lens has been cut/turned from the 
moulded bottom, the material of the first member and the second will be 
divided by a coloured ring like zone. 
In one particular use of this aspect of the present invention, the 
colouring of the casting mould can be used to provide in the finished 
contact lens a lens locating tint which can be introduced into the 
finished lens without any inconvenience to the lens wearer, and little 
additional cost, whilst providing the advantages associated with locater 
tints. 
Alternatively, the colouring of the casting mould in the fashion disclosed 
can be used to provide a ring of distinct colour where required. 
Additionally it should be noted that because the casting mould has distinct 
cast moulding areas i.e., one or more receptive wells, and a mould each of 
the distinct zones of the finished contact lens can be coloured or not 
separately to provide an adaptable method of manufacturing contact lens. 
The casting moulds for use with the method of the present invention are 
obviously formed with sufficient thickness of material to provide the 
strength necessary to ensure that no deformation is experienced during the 
casting of the monomer materials, and subsequent curing/polymerisation 
thereof. However, the end wall of the casting mould should not be of such 
thickness that it begins to interfere with the optical properties of the 
finished contact lens. 
Preferably, the end wall of the casting mould has a thickness in the region 
of 0.1 mm to 2 mm. 
In a majority of cases where the method of manufacturing a contact lens in 
accordance with the present invention is used, the casting mould for use 
therewith has an end wall which is of a fairly uniform thickness, with 
respect to the side wall of the casting mould. 
However in some circumstances it is envisaged that the thickness of the end 
wall will vary across said end wall. Now in the situation that the end 
wall has a conical inward displacement the variation in thickness of the 
end wall may occur up the sides of the cone to its apex. Further in the 
situation where the inward displacement is an upstanding cylinder which 
forms a second receptive well for containing a suitable material and 
polymerisation thereof the variation in thickness of the end wall may 
occur around the side(s) of the upstanding cylinder. 
Clearly, with regard to the thickness of the end wall of the casting mould 
the above comments mope readily apply to casting moulds which have two 
receptive wells for the casting of material. Now, in the situation where 
the casting mould has a solidly formed inward displacement, the 
limitations mentioned above will not apply at least to the area of the 
inward displacement. 
The present invention may be used to manufacture contact lenses from any 
combination of materials of types of materials, for example hard and hard, 
hard and soft, and soft and soft. 
The term "hard contact lens material" is well known in the industry and 
within the general terms there is included a large variety of materials. 
Most preferably, the hard contact lens material is a rigid gas permeable 
material, such as Fluorocon. 
The term "soft contact lens material" is well known in the industry, and is 
the general term used in respect of hydrogel materials, that is materials 
which can be readily hydrolised/swollen under the action of water. 
Typically these materials are very soft and flexible in nature once 
hydrolysed. 
Alternatively the "soft contact lens material" may be a silicone. 
Preferably, the soft contact lens material is a hydrogel, such as that 
disclosed in co-pending application No. 641273.

DESCRIPTION OF PREFERRED EMBODIMENTS 
Now referring to FIG. 1 of the accompanying drawings there is shown a 
casting mould 1 for use in a method of manufacturing a contact lens in 
accordance with the present invention. 
The casting mould 1 is of cylindrical construction having a side wall 2 and 
an end wall 3. The end wall 3 is inwardly displaced into the space defined 
within the side wall 2, and is of conical construction. 
With this configuration the casting mould 1 defines two receptive wells for 
holding liquid material. The first of these wells A is defined by surface 
4 of the end wall 3, and is external of the cylindrical side wall 2 of the 
casting mould 1. The second of the receptive wells B is defined by surface 
5 of the end wall 3 and the cylindrical side wall 2 of the casting mould 
1. The wells A and B are located on opposite sides of the end wall 3. 
The end wall 3 of the casting mould has a thickness of 1.0 mm. 
Now referring to FIGS. 2 to 6 of the accompanying drawings, a method of 
manufacturing a contact lens in accordance with the present invention will 
now be described. 
The casting mould 1 is located so that the receptive well A thereof is 
capable of holding liquid monomeric material. The liquid monomeric 
material of a first material is poured into the receptive well A and 
polymerised. 
When this polymerisation has been completed the receptive well A is filled 
with a hardened mass of polymeric material which is retained in place by 
the interaction of the cast monomeric material with the material of the 
end wall 3. The mould is now reversed and the receptive well B filled with 
liquid monomer of a second material which is then polymerised. 
Once this second polymerisation operation is completed, a button as shown 
in FIG. 3 is formed. 
In order to complete the manufacture of the contact lens a first optical 
surface 6 is machined onto the button as shown in FIG. 4. The button is 
reversed and the second optical surface 7 is machined thereon. 
A contact lens so formed is shown in FIGS. 5 and 6 of the accompanying 
drawings. This contact lens comprises: 
a skirt 8 formed from the material cast into the receptive well B of the 
casting mould 1 and 
a central area 9 formed from the material cast into the receptive well A of 
the casting mould 1. 
Once the contact lens has been machined from the button as described above, 
the material of the skirt 8 can then be hydrolysed/and swollen to provide 
the material with its soft and pliable nature. This is done in accordance 
with the well known procedures currently used in the industry. 
The actual diameter of the central area 9 formed in the contact lens, 
because of the conical nature of the receptive well A of the casting mould 
1 is dependent upon the depth of cut used to form the contact lens from 
the button. Therefore by adjusting the depth of cut used to form the 
contact lens from the button the size of the central area 9 can be 
adjusted to the wearer's requirements and the lighting background in the 
area he lives. 
It will also be noticed that the interface between the sheet 8 and the 
central area 9 is quite marked in appearance. The effects of this 
interface can be adjusted by changing the angle of the conical end wall 3 
and the thickness of the lens to provide the required characteristics. 
EXAMPLE 1 
A contact lens as described above is formed by the above method as follows 
using a casting mould 1 which is formed with an end wall that is made from 
polymethyl methacrylate (PMMA). 
The central area 9 (formed from the monomer material cast into receptive 
well A of the casting mould 1) is formed from a monomer mixture with the 
following composition: 
______________________________________ 
3 Methacryloxy propyl tris (trimethyl-siloxy) 
45% 
silane 
1,3 bis (3 methacryloxypropyl) tetra bis 
15% 
(trimethyl siloxy) disiloxane 
Methyl methacrylate 25% 
Methacrylic acid 9% 
Ethylene glycol di methacrylate 
5.5% 
2,2 azobis (2 methyl propane nitrile) 
0.5% 
______________________________________ 
The skirt 8 (formed from the monomer material cast into receptive well B of 
the casting mould 1) is formed from a monomer mixture with the following 
composition: 
______________________________________ 
Hydroxy ethyl methacrylate 
69% 
Polyethylene glycol 30% 
Ethylene glycol di methacrylate 
0.5% 
2,2 azobis (2 methyl propane nitrile) 
0.5% 
______________________________________ 
The contact lens is then cut with the central area 9 having a diameter of 
9.00 mm and the skirt 8 having a diameter of 14.00 mm. 
Now turning to FIG. 7A of the accompanying drawings which shows a cast 
moulded button B, and a cross-sectional view and plan view of a contact 
lens manufactured from the button B. 
The button B is cast moulded with a casting mould 20 which is incorporated 
into the finished button B. The casting mould 20 is manufactured from 
polymethylmethacrylate and is of generally circular configuration having a 
side wall 21 and a base wall 22. The base wall 22 of the casting mould is 
inwardly displaced in the shape of a regular cone into the space 
surrounded by the side wall 21, with the apex of the cone in line with the 
central axis of the side wall 21. 
With the shaping of the casting mould as described above two receptive 
wells suitable for casting of polymeric material are defined; these are: 
space S defined by the side wall 21 and the base wall 22 and into which the 
material from which the second member is formed is cast; and 
space T defined by the inward displacement in the base wall 22 and into 
which the material from which the first member is formed is cast. 
In one particular example the material cast into the space S is a hydrogel 
material which is of the following composition 
______________________________________ 
Hydroxyethyl methacrylate 69% 
Polyethylene glycol 30% 
Ethylene glycol dimethacrylate 
0.5% 
2.2 azobis (2 methylpropane nitrile) 
0.5% 
and the material cast into the space T is 
3 Methacryloxypropyltris(trimethyl-siloxy) 
45% 
silane 
1,3 bis(3 methacryloxy propyl)tetrabis 
15% 
(trimethylsiloxy) disiloxane 
Methylmethacrylate 25% 
Methacrylic acid 9% 
Ethylene glycol dimethacrylate 
5.5% 
2,2 azobis (2 methyl propane nitrile) 
0.5% 
______________________________________ 
Now in FIG. 7 the outline CL in the button shows the position of a contact 
lens which is to be machined from the button. 
Further there is shown in FIG. 7B a cross sectional view and a plan view of 
a contact lens so machined from the button. The lens has an outer member 
23 and an inner member 24, these members are separated from one another by 
the moulding cast 20. 
Now turning to FIGS. 8A and 8B of the accompanying drawings there is shown 
in FIG. 8A another cast moulded button B and in FIG. 8b a cross-sectional 
view and a plan view of a contact lens manufactured from the button B. 
The description of this button B and the contact lens CL formed therefrom 
are very similar to that discussed with reference to FIGS. 7A and 7B and 
consequently like numerals have been used to indicate like components. 
Now in this particular case the differences are in the shape and position 
of the inward displacement in the base wall 22. 
In this case the inward displacement in the base wall is again conical in 
shape, however is slightly offset from the axis which runs through the 
casting mould case 20. The net result of this can be clearly seen from the 
plan view of the contact lens, illustrated in FIG. 8B in that the first 
member is elliptical in shape, and not circular as in the example 
discussed with respect to FIGS. 7A and 7B of the accompanying drawings. 
The button B and the contact lens CL formed therefrom are formed from the 
same materials as discussed with regard to FIGS. 7A and 7B of the 
accompanying drawings. 
Now turning to FIGS. 9A and 9B of the accompanying drawings in which there 
is shown another form of cast button B, with cross-sectional view and plan 
view of a contact lens manufactured therefrom. 
The description of this button and the contact lens formed therefrom are 
very similar to that discussed with reference to FIGS. 7A and 7B of the 
drawings, and consequently like numerals have been used to indicate like 
components. 
In this particular case the differences are in the shape and position of 
the inward displacement of the base wall 22. 
The inward displacement in the base wall 22 is cylindrical in shape, the 
central axis of the displacement being offset from the central axis of the 
moulding cast. 
Consequently, when the contact lens is machined from the cast button B as 
with the contact lens discussed with regard to FIGS. 8A and 8B of the 
accompanying drawings the first member is elliptical in shape, and not 
circular. 
The button B and the contact lens CL formed therefrom are formed from the 
same materials as discussed with regard to FIGS. 7A and 7B of the 
accompanying drawings. 
Now turning to FIGS. 10A and 10B of the accompanying drawings in which 
another form of cast button B, and contact lens manufactured therefrom are 
shown. 
The description of this button and the contact lens formed therefrom are 
very similar to that discussed with reference to FIGS. 7A and 7B of the 
accompanying drawings and, consequently, like numerals have been used to 
describe like components. 
In this case the differences are in the contraction of the casting mould 20 
in the vicinity of the base. Previously, the casting mould 20 has been 
made so that the side wall 21 and the base wall 22 are of equivalent 
thickness. In the example now being illustrated the base wall 22 is of 
much greater thickness than the side wall 21. The net effect of this is 
clearly shown in the plan view of the contact lens machined from the 
button B, where the barrier between the first and second members of the 
contact lens provided by the casting mould 20 is much thicker than with 
the previous examples. Further, by having a higher refractive index of the 
casting mould material, a concentric bifocal lens is prepared. 
The button B and the contact lens CL formed therefrom are formed with the 
same materials as discussed with regard to FIGS. 7A and 7B of the 
accompanying drawings. 
Now turning to FIGS. 11A and 11B of the accompanying drawings, there is 
shown another form of cast button B, and cross-sectional view and plan 
view of a contact lens manufactured therefrom. 
In this case a casting mould 30 is manufactured from polystyrene, and 
comprises a cylindrical side wall 31 with a base wall 32. The base wall 32 
has an upstanding solid post member 33 which has an axis slightly offset 
kept parallel to the equivalent axis of the casting mould as a whole. 
Now the casting mould 30 in this case may be manufactured by injection 
moulding into this particular fashion or, alternatively, a casting mould 
similar to that shown in FIGS. 9A and 9B of the accompanying drawings may 
be used with the space T having polymer identical to that from which the 
casting mould 30 is made, cast and polymerised therein. 
In any event the casting mould only defines one receptive well for the 
casting of material to form the button. In this case polymeric material of 
the following composition is cast into the receptive well. 
______________________________________ 
Hydroxy ethyl methyl/methacrylate 
69% 
Polyethylene glycol 30% 
Ethylene glycerol dimethacrylate 
0.5% 
2,2 azobis (2 methyl propane nitrile) 
0.5% 
______________________________________ 
Once polymerised the cast button B may be machined to form a contact lens 
which has a first member 34 formed from the material of the upstanding 
post of the casting mould and a second member formed from the material 
cast into the receptive well of the mould. 
Finally turning to FIGS. 12A and 12B of the accompanying drawings a seventh 
basic design of cast button B and contact lens CL formed therefrom is 
shown. 
In this particular example, the cast button B is formed using a casting 
mould 41 which is incorporated into the cast button B. 
The casting mould 41 in this case is manufactured from an optically clear 
material, such as polystyrene. The mould 41 includes; 
an end wall 42, 
a first side wall 44 which circumferentially surrounds the periphery of the 
end wall 42 and is connected thereto; and 
a second side wall 43 which is connected to the end wall 42 within the 
space defined by the first side wall 44 and is upstanding therefore. 
A casting mould 41 of this fashion defines two receptive wells 45 and 46 
into which polymeric monomer material can be cast in order to enable the 
forming of a cast button B, one of which receptive wells 46 is 
circumferentially surrounded by the other receptive well 45. 
The receptive well 45 is defined by the inner surfaces of the first side 
wall 44 and the end wall 42 and the outer surface of the second side wall 
43. 
The receptive well 46 is defined by the inner surfaces of the second side 
wall 43 and the end wall 42. The second side wall 43 constitutes an inward 
displacement of the end wall 42. Both of the wells 45, 46 are located on 
the same side of the end wall 42. 
In the formation of a cast button B liquid monomeric material is cast into 
the receptive wells 45 and 46 and polymerised. 
The method of casting a button using this casting mould 41 may be identical 
with that disclosed above for the formation of the casting button. However 
with the casting button of the above type the receptive wells 45 and 46 
are disposed on the same side so the liquid monomer material may be cast 
into the appropriate receptive well and polymerised/cured simultaneously. 
That is to say the first polymerising/curing step of the earlier detailed 
method has been leftout. 
In one particular example the liquid monomeric material cast into receptive 
well 45 comprises 
______________________________________ 
Hydroxyethylmethacrylate 69% 
Polyethylene glycol 30% 
Ethylene glycol dimethacrylate 
0.5% 
2,2 azobis(2 methylpropanenitrile) 
0.5% 
______________________________________ 
and the liquid monomeric material cast into receptive well 46 comprises 
______________________________________ 
3 Methoxyloxypropyltris(trimethyl- 
45% 
siloxyl silane 
1,3 bis(3 methacryloxypropyl)tetra 
15% 
bis(trimethylsiloxy)disiloxane 
Methylmethacrylate 25% 
Methacrylic Acid 9% 
Ethylene glycol dimethacrylate 
5.5% 
2,2 azobis(2 methylpropanenitrile) 
0.5% 
______________________________________