Bifocal contact lens

A bifocal contact lens includes a near vision portion having a first radius curvature and a far vision portion concentric with the near vision portion and having a second radius of curvature. A junction is formed where the near vision and far vision portions meet. This junction is polished to remove the sharp demarkation between far and near vision portions so that an annulus of multiple radii is formed where the two vision portions meet. This annulus prevents double vision associated with sharp junctions between far and near portions.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates generally to the field of optics and, in 
particular, to a bifocal corneal contact lens. 
2. Description of the Related Art 
Although refracting contact lenses have been in existence for nearly 100 
years, they have generally been unsuccessful when adapted for use as a 
bifocal lens. Bifocal contact lenses have been commercially available for 
the past 30 years but, for various reasons have not proven to be 
successful. Generally, these lenses tend to have either good distance 
vision with poor reading vision, or good reading vision with poor distance 
vision. Part of the reason for this is the delineation between near and 
far vision portions of the lens created by polishing. 
One type of best known bifocal contact lens is referred to as the crescent 
seg fused bifocal. A segment of higher index plastic is fused into a lower 
index plastic matrix to create a reading section. This reading section is 
held in correct position on the eye by the use of prism for ballast. 
However, edema has been induced by such lenses because of their use of 
PMMA plastic. Thus, the wearing time is diminished, and the lenses are 
also uncomfortable due to the creation of a prism and the weight of the 
lens. 
Other attempts to create a viable bifocal contact lens have led to the use 
of a lens which has concentric far and near portions. Referring to FIGS. 1 
and 2, a contact lens 10 has two concentric portions, a far distance 
portion 12 which is circular in shape, and a near distance portion 14 
which is annularly shaped around the central circular portion. 
In the manufacturing process, the far and near vision portions are cut and 
polished to achieve the required refraction. The polishing occurs on the 
anterior surface 16 of the lens 10 while rotating same and applying a 
polishing tool and polishing fluid to the anterior surface 16. 
The polishing process leaves the anterior surface with different radii of 
curvature for the different vision zones. As seen in FIG. 1, the far 
distance portion 12 has a flatter curvature than the near distance portion 
14. The difference in curvature results in the formation of a sharp, 
annular junction 20 where the curvature radius changes between the two 
vision portions. This junction creates two problems. First, it creates a 
line between the near and far vision portions which, when the lens moves 
on the eye, creates an image jump or double vision. Secondly, the junction 
20 creates a source of irritation for the user because of the 
non-curvilinearity of the anterior surface 16. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a bifocal contact lens in 
which there is no line or sharp junction between far and near portions 
which creates image jump or double vision. 
Another object of the present invention is to provide a bifocal contact 
lens which has a more curvilinear anterior surface, thus rendering the 
lens more comfortable to wear. 
Another object of the present invention is to provide a method of 
manufacturing a bifocal contact lens using simple polishing techniques. 
To attain the above and other objects of the invention, a bifocal contact 
lens is provided which includes a near vision portion having a first 
radius of curvature, a far vision portion concentric with the near vision 
portion and having a second radius of curvature, a junction being formed 
where the near vision and far vision portions meet, and an aspheric curved 
annulus formed at the junction of the near vision and far vision portions 
to smoothly converge the first and second radii of curvature. 
In another aspect of the present invention, a method of making a bifocal 
contact lens includes forming a near vision portion having a first radius 
of curvature, forming a far vision portion concentric with the near vision 
portion and having a second radius of curvature, a junction being formed 
where the near vision and far vision portions meet, and forming a aspheric 
curved annulus at the junction of the near vision and far vision portions 
to smoothly converge the first and second radii of curvature. 
These and other features and advantages of the bifocal contact lens 
according to the present invention will become more apparent with 
reference to the following detailed description and drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
As described above, the concentric bifocal contact lens 10 illustrated in 
FIGS. 1 and 2 has a relatively sharp junction 20 formed where the near 
vision portion meets the far vision portion 12. The junction results 
substantially from the change in radius of curvature from the relatively 
flat radius for the far vision portion 12 to the more curved radius for 
the near vision portion 14. The different radii of curvature results from 
the lathing and polishing steps which are used to obtain the desired 
amount of refraction for each portion of the lens. 
According to the present invention, as illustrated in FIGS. 3 and 4, the 
bifocal contact lens 10 has a near vision portion 14 which has a first 
radius of curvature, and a far vision portion 12 concentric with the near 
vision 14 and having a second radius of curvature. Although there is a 
"junction" between the two vision portions, according to the present 
invention the junction is an aspheric curved annulus 22 made by an 
aspheric cut approximately centered over the original sharp junction 20. 
This cut is made by polishing at the junction of the near vision and far 
vision portions to smoothly converge the first and second radii of 
curvature. The central, circular portion of the lens, which is between 3.5 
and 5 millimeters in diameter, is the distance portion 12, and the rest of 
the lens is the reading or near vision portion 14. 
By cutting an aspheric surface between the distance and reading portions of 
the lens, approximately 1 millimeter wide, there is no demarkation visible 
between the two sections and therefor the eye will not pick up the jump 
between distance and reading sections of the lens. As illustrated in FIG. 
4, the aspheric surface is a curved annulus 22 approximately centered 
where the junction used to be. By polishing this area, the sharp junction 
is removed and, in effect, the new junction is an annular zone 22 having 
numerous radii. 
The lens according to the present invention can be fitted like any standard 
lens and manufactured in any type of material, soft or rigid. The ideal 
fit of the lens is an aspheric back curve parallel to the cornea. The lens 
diameter may vary according to individual requirements. 
In the method according to the present invention, the near vision and far 
vision portions are formed by polishing according to known techniques. In 
forming the aspheric curved annulus 22, which has the affect of removing 
the sharp junction 20, a polishing tool is applied to the zone illustrated 
in FIG. 4 by the numeral 22. The polishing tool may use a polishing cloth 
and a heavy liquid polish. In effect, polishing this zone blends the 
distance portion and near portions so that no line will be visible. The 
polishing cloth may be pitch or cotton, or other suitable material. The 
polishing fluid may be any of the known and commercially available 
polishing fluids. 
As described herein, the phrase "sharp junction" is a relative term and 
refers to a substantial circular line formed by the abrupt change of 
radius of curvature from one vision zone to the next. The invention is 
directed to a method of making a lens in which the junction is removed by 
polishing only in a small area centered on the junction. The invention 
also is directed to a lens having the junction removed, so that an 
aspheric cut replaces the sharp junction. The cut is an annular surface of 
multiple radius, or interpolated radii between the radius of the near 
vision portion and the radius of the far vision portion. 
Numerous modifications and adaptations of the present invention will be 
apparent to those so skilled in the art, and thus, it is intended by the 
following claims to cover all such modifications and adaptations which 
fall within the true spirit and scope of the invention.