Method of making toric lenses

A method of making plastic toric lenses by casting a liquid monomer in a container having the required toric curve on the bottom of the container, polymerizing the monomer to form a solid having a toric optical surface formed within the container and cutting a second optical surface on the solid lens material with the container supporting the lens material during the cutting and polishing operation. The container or mold used for casting the lens is made by applying pressure to two opposing sides of a heat softened resinous cylinder to change the shape of the cylinder from a circle to an ellipse, and to change the bottom shape of the cylinder from a spherical surface to a toric surface. The cylinder is then allowed to cool before the pressure is removed.

FIELD OF THE INVENTION 
The use of plastic materials for making optical lenses has increased 
rapidly for the past ten years. This is due to the availability of better 
plastic materials and the physical advantages of the plastic resins for 
specific applications such as ophthamic lenses. To technology for the 
production of high quality plastic lenses has not kept pace with the 
material supply industry. It is important to advance both areas if the 
full potential is to be realized. 
Plastic lenses offer many advantages over glass lenses. They are much 
lighter in weight and resist breakage. The cost of making high quality 
lenses has been high due to the problems caused by the shrinkage of the 
monomer when polymerized, which often breaks the expensive molds. 
STATE OF THE ART 
The current lens molds are fabricated from steel or glass, each mold is 
individually ground and polished to the required specifications. To 
achieve accurate reproduction of the bifocal and toric molds is most 
difficult and expensive. 
An object is to provide a process for making inexpensive toric molds which 
may be made to identical specifications. 
Another object is to provide a process whereby standard masters may be used 
to produce a large quantity of replica molds. 
The replica mold also serves as a holding fixture during the cutting and 
polishing of the second optical surface.

THE LENSES ARE MADE AS FOLLOWS 
A master positive mold is made from glass or stainless steel or other 
materials which will withstand the molding temperatures. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The master mold, 1 FIG. 1, is placed in a sleeve, 4 FIG. 1, a molding grade 
of a resinous material such as polyimide, polycarbonate, 
polymethylpentene, polyethylene, polypropylene, nylon or other molding 
material is placed in the sleeve, 4 FIG. 1. The sleeve and it's contents 
are heated to the softening point of the molding material, pressure is 
applied to form the lens mold, 3 FIG. 1. The sides of the master mold, 1 
FIG. 1, have been cut to a smaller diameter to provide the opening, 5 FIG. 
1. When sufficient heat and pressure have been applied, the molding 
compound, 3, will fill the area around the positive mold, 1, forming a 
cup-like cavity with a curved optical surface, 2 FIG. 1, at the bottom. 
Either injection or compression molding may be used to produce the lens 
molding container. The lens container, 3 FIG. 1, is removed from the 
molding sleeve, 4 FIG. 1, and the optical mold, 1 FIG. 1, is also removed. 
The resinous mold, 3 FIG. 1, is placed in an oven and heated to a 
temperature below the distortion temperature of the resinous material. The 
working temperature will be below the glass transition temperature and 
below the temperature at which changes in the curvature of the optical 
surface, 2 FIGS. 1 and 2, occur. The most desirable temperature is 
7.degree. C. below the temperature at which a change in the curvature of 
the optical surface, 2 FIGS. 1 and 2, occurs. The resinous mold, 3 FIGS. 1 
and 2, is heated to the working temperature and pressure is applied to 
opposing exterior sides of the mold, distorting the shape of the mold, 
including the optical surface, 2 FIGS. 1 and 2, which assumes a toric 
shape. Pressure is applied to the sides of the heated cylinder, 3 FIGS. 1 
and 2, changing the shape from a round cylinder to an ellipse. The 
spherical surface, 2 FIGS. 1 and 2, will change to a toroidal shape when 
the cylinder is flattened to an ellipse. A toric surface intersects a 
sphere on an ellipse, therefore, if a circular segment of a sphere is 
distorted to an ellipse the spherical surface becomes a toric surface. An 
elliptical segment of a sphere will also become a toric if the ellipse is 
forced to a circle. The difference in radius between the two toric 
meridians is not of a great magnitude, ranging in linear progression as 
follows: 0.25 diopter toric =0.03 millimeter difference in radius, 0.50 
diopter toric =0.06 millimeter difference in radius, 1.00 diopter toric 
=0.12 millimeter difference in radius, and 2.00 diopter toric =0.24 
millimeter difference in radius. The above degree of difference in radius 
is for a refractive index of 1.488 at the D sodium line and an 8.00 m/m 
spherical radius. A diopter is the reciprocal of the focal length 
expressed in meters. The distortion required is of a rather small degree 
compared to the size of the componenets involved. The pressure required to 
effect the desired distortion is applied to the heated resinous lens mold 
and maintained until the resinous mold is allowed to cool to ambient 
temperature. After cooling, the pressure is removed and the toric present 
on surface, 2 FIG. 2, is measured and confirmed before the liquid monomer, 
6 FIG. 2, is added. 
CASTING THE TORIC OPTICAL SURFACE 
A liquid or syrup monomer material containing a suitable catalyst, 6 FIG. 
2, is placed over the toric optical surface, 2 FIG. 2, and covered to 
prevent evaporation with a cover, 7 FIG. 2, an air space, 8 FIG. 2, is 
provided. The liquid monomer is polymerized to form a solid. Microwave 
energy or heat may be used to speed the polymerization process. 
Thermosetting and crosslinked materials may be used to produce lenses 
which are dimensionally stable. This process is suitable for the 
production of toric soft contact lenses which cannot be made by 
compression or injection molding techniques. 
CUTTING THE SECOND OPTICAL SURFACE 
It is not necessary to remove the hardened plastic lens material, 6 FIG. 3, 
from the mold, 3 FIG. 3, before cutting the convex curve, 9 FIG. 3. The 
mold, 3 FIG. 3, may be placed in a suitable lathe and curvature, 9 FIG. 3, 
cut and polished. The finished lens, 6 FIG. 4, having the molded toric 
concave surface, 2, and the convex curvature, 9, which was cut and 
polished without being removed from the disposable mold, 3 FIG. 4. The 
cuplike device has served as a container for the monomer, 6 FIG. 2, 
provided the molded toric optical surface which for contact lens 
production may be two or more toric segments providing the required 
optical zone, peripheral curves and lens diameter. The cup-like mold, 3 
FIG. 3, also serves as the holding block to facilitate cutting to the 
required thickness. The thickness of the cup bottom may be measured before 
adding the liquid monomer and measurements may be taken during the cutting 
operation and the lens thickness determined by subtracting the thickness 
of the cut bottom. The cup, 3 FIG. 3, which adheres strongly to the lens 
also serves as a holding fixture during the polishing operation. After the 
toric lens is processed to the required specifications, the toric lens is 
removed by sharply flexing the holding fixture, 3 FIG. 4, separating the 
finished toric lens from it's support. 
Various modifications can be made without departing from the spirit of this 
invention or the scope of the appended claims. The constants set forth in 
the disclosure are given as examples and are in now way final or binding. 
In view of the above, it will be seen that the several objects of the 
invention are achieved and other advantages are obtained. As many changes 
could be made in the above construction and method without departing from 
the scope of the invention, it is intended that all matter contained in 
the above description shall be interpreted as illustrative and not in a 
limiting sense.