EP0073816A1

EP0073816A1 - Variably blended bifocal lens

Info

Publication number: EP0073816A1
Application number: EP19820901201
Authority: EP
Inventors: Alban Judson Lobdell; Tyrus L. Weller
Original assignee: Camelot Industries Corp
Current assignee: Camelot Industries Corp
Priority date: 1981-03-09
Filing date: 1982-03-01
Publication date: 1983-03-16
Also published as: WO1982003129A1

Abstract

Lentille ophtalmique (10) multifocale en une piece possedant une zone de melange (14) entre les differentes parties de la lentille afin de rendre moins visible l'intersection entre ces parties. La zone de melange (14) possede une largeur variable, et, notamment, une largeur relativement etroite aux emplacements (16) utilises frequemment pour la vision de maniere a permettre d'obtenir une zone reduite de distorsion optique a ces emplacements, tout en etant relativement large a d'autres emplacements (17) de la lentille qui sont utilises moins souvent pour la vision afin de rendre moins visible de maniere plus efficace l'intersection a ces emplacements.One-piece multifocal ophthalmic lens (10) having a mixing zone (14) between the different parts of the lens in order to make the intersection between these parts less visible. The mixing zone (14) has a variable width, and in particular a width that is relatively narrow at the locations (16) frequently used for vision so as to allow a reduced area of optical distortion to be obtained at these locations, while being relatively wide at other locations (17) of the lens which are used less often for vision in order to make the intersection at these locations less effective.

Description

VARIABLY BLENDED BIFOCAL LENS

Technical Field

The present invention relates generally to the field of multifocal ophthalmic lenses and, more particularly, to a one-piece bifocal lens wherein the sharp boundary normally present between the bifocal add portion and the distance portion of the lens is blended together in a variable manner so as to achieve not only desirable optical characteristics, but suitable cosmetic properties as well.

Background Art

Most plastic multifocal lenses are constructed from a single piece of material and the power differential is achieved by providing different areas of the lens with different surface curvatures and hence, different focal lengths. One common type of bifocal lens is often referred to as an O-Style lens and consists of one sphere of relatively short radius of curvature (the reading segment) applied to a second, larger radius sphere (the distance portion). As is known, the intersection of two spheres is normally a circular line and, as a result, in the standard O-Style lens, the reading segment of the lens is clearly delineated from the remainder of the lens by a circular line formed on the surface of the lens. For cosmetic reasons, the presence of such a line is not desirable and, accordingly, efforts have been made to render it less visible. It is known in the prior art, for example, that this circular line can be made less visible by a technique known as "blending" in which the surface of the lens in the vicinity of the line is ground and polished to an extent sufficient to make the line essentially disappear. See, for example, U. S. Patent Nos. 1,413,945 and 3,010,366 wherein this concept is discussed.

Although this blending technique is useful, and does render the lens more marketable, it is not fully satisfactory. Specifically, the area of the lens where the actual blending occurs suffers from severe optical distortion, and is not very useful for vision purposes. To make the blending zone narrow in width will have the positive effect of minimizing the area having this severe optical distortion but, at the same time, this will tend to make the transition area more visible. On the other hand, by providing a wide blending zone, the transition can be made virtually invisible, but this will result in a larger area of distortion which cannot be used for vision purposes.

Disclosure of the Invention

Recognizing the above conflict, the present invention is directed to a bifocal lens wherein the sharp boundary between the bifocal add and the distance portion is variably blended. Specifically, the lens is blended by different amounts in different portions of the lens depending on the particular lens characteristics that are desired.

In accordance with a presently most preferred embodiment, for example, a typical O-Style lens would be provided with a relatively narrow blended zone at the top of the bifocal portion, and a relatively wide blending zone at the bottom of the bifocal portion with intermediate widths inbetween. With this structure, the best optical performance will be retained at the top of the bifocal segment which is used the most for vision, while the maximum cosmetic hiding of the segment will be near the bottom thereof which is an area of the lens rarely looked through.

The extent and location of the blending can be varied within wide limits depending on the particular type of lens being processed and upon other considerations as will become apparent hereinafter.

Brief Description of the Drawings

FIG. 1 illustrates a variably blended O-Style bifocal lens in accordance with a presently preferred embodiment of the invention. FIG. 2 illustrates a second embodiment of the invention.

Best Mode for Carrying Out the Invention

FIG. 1 illustrates a variably blended O-Style bifocal lens in accordance with, a presently most preferred embodiment of the present invention. The lens is generally represented by reference number 10 and includes a distance portion 11, which constitutes the major portion of the lens, and is used by the wearer for viewing distant objects, and the bifocal addition or reading portion 12, which is used by the wearer to view objects located at a reading distance. Lens 10 will usually be of polymer material manufactured in a mold by casting it against a mold surface as is known in the art, although it could also be of glass as well, if desired. The lens is of onepiece construction in that it is formed from a single piece of material with the power differential between portions 11 and 12 being achieved by providing them with different surface curvatures. Specifically, distance portion 11 has a spherical surface of relatively long radius of curvature, while the reading portion 12 has a spherical surface curvature of much shorter radius.

As is known, the intersection of two spherical surfaces is a circle, and, accordingly, under normal conditions the intersection of lens areas 11 and 12 would be a circular line represented in FIG. 1 by dotted line 13. This line would normally be quite visible, and because of this, many people who require bifocal lenses for vision purposes, are hesitant to wear them because of the belief that they are noraally associated with advancing or middle age. It is known, however, that if this circular line can be rendered substantially invisible, then it is not nearly as apparent that the lens is a bifocal lens, and many people would be more favorably disposed toward wearing them.

The technique devised in the prior art for rendering this line substantially invisible, or, at least, less visible, is a blending process which consists of grinding or polishing away the line by gradually merging the two spherical surfaces into one another. In the case of polymer lenses, it is actually the mold surface that is smoothed out in this way to form the blended lens. Reference number 14 generally identifies the blending area, and in the prior art this area is ring shaped and of uniform thickness throughout and is formed by means of a spinning grinding tool as is known in the art. This blended area is really not very useful for viewing purposes because the blending introduces substantial optical distortion into the lens surface. By making this blending zone relatively narrow, the area of optical distortion can be minimized, however, at the same time, the transition area is rendered more visible and, thus, less desirable cosmetically. To make the blending zone relatively wide will permit the transition to be made virtually invisible, but, of course, there will then be a larger area of the lens that is not usable for viewing purposes.

The present invention recognizes this conflict and provides a lens which is variably blended as is illustrated in FIG. 1. Specifically, by the present invention, the lens is provided with a relatively narrow blending zone 16 at the top of the bifocal segment and a relatively wide blending zone 17 at the bottom of the segment with a zone of intermediate width being present in between. This design permits optical performance of the lens to be maximized at the top of the bifocal segment which is an area very commonly used for vision, and, at the same time, allows cosmetic hiding to be maximized at the bottom of the bifocal segment which is an area of the lens rarely looked through.

In a typical O-Style lens, the width of the bottom portion of the blended area can be two to three times as wide as the narrow top portion area. For purposes of example only, the bottom portion 17 could be perhaps, 9 millimeters wide while the top portion 16 could be about 3 millimeters wide. These widths, of course, would be a function to some extent of the power difference between the two portions of the lens, inasmuch as a higher add would require a greater amount of blending to render the dividing line invisible.

A number of methods can be used to accomplish blending of the mold surface (or of the lens itself in the case of glass lenses). For example, the blending can very readily be accomplished by a conventional spinning polishing tool which is designed so that the center of pressure will be off-center towards the bottom of the segment so as to cause the variable blending to take place. The invention could also readily be practiced with lenses other than the standard O-Style lens. FIG. 2 for example, illustrates a different kind of multifocal lens 20 (which we may consider as a type of O-Style lens) wherein the round reading segment 21 runs into the bottom of the lens. With this lens, the area of maximum blend will preferably be adjacent the bottom edge of the lens in the vicinity of areas 24 while the area of minimum blend 26 is again at the top of the segment. The invention could also be practiced with yet other types of multifocal lenses as well, and because the invention can take many other forms, it should be readily understood that it is to be limited only insofar as is required by the scope of the following claims.

Claims

1. In a multifocal ophthalmic lens including a first lens surface portion having a first radius of curvature, a second lens surface portion having a second radius of curvature different from said first radius of curvature, and a blended area between said first and second lens surface portions for rendering the intersection between said lens surface portions less visible; the improvement comprising wherein the size of said blended area varies at different locations between said first and second lens surface portions.

2. A multifocal ophthalmic lens as recited in Claim 1 wherein the width of said blended area varies at different locations between said first and second lens surface portions.

3. A multifocal ophthalmic lens as recited in Claim 2 wherein the width of said blended area is relatively narrow at a location of the lens that is more frequently used for vision purposes to provide a relatively reduced area of optical distortion at such location, and is relatively wide at another location of the lens that is less frequently used for vision purposes to more effectively render the intersection between said first and second lens surface portions less visible at such other location.

4. A multifocal ophthalmic lens as recited in Claim 3 wherein said first lens surface portion comprises a distance portion of relatively long radius of curvature and said second lens surface portion comprises a reading portion of relatively short radius of curvature, and wherein said blended area is relatively narrow adjacent the top of said reading portion and relatively wide adjacent the bottom of said reading portion.

5. A multifocal ophthalmic lens as recited in Claim 4 wherein said lens comprises a bifocal lens.

6. A multifocal ophthalmic lens as recited in Claim 5 wherein said lens comprises an O-Style lens.

7. A multifocal ophthalmic lens as recited in Claim 5 wherein said lens comprises a one-piece polymer lens.

8. A multifocal ophthalmic lens as recited in Claim 5 wherein said lens comprises a glass lens.

9. A one-piece multifocal ophthalmic lens comprising; a. a first lens surface portion of relatively long radius o'f curvature; b. a second lens surface portion of relatively short radius of curvature; and c. a blended area between said first and second lens surface portions for rendering the intersection therebetween less visible, said blended area differing in width at different locations between said first and second lens surface portions.

10. A multifocal ophthalmic lens as recited in Claim 9 wherein said blended zone is relatively narrow at a location of the lens more frequently used for vision purposes to provide a narrow area of optical distortion at such location, and is relatively wide at another location of said lens that is less frequently used for vision purposes to more effectively render the intersection less visible at such other location.

11. A multifocal ophthalmic lens as recited in Claim 10 wherein said blended zone is relatively narrow adjacent the top of said second portion, and relatively wide adjacent the bottom of said second portion.

12. A multifocal ophthalmic lens as recited in Claim

11 wherein said lens comprises an O-Style lens.

13. A multifocal ophthalmic lens as recited in Claim

12 wherein said lens comprises a polymer lens.

14. A multifocal ophthalmic lens as recited in Claim 12 wherein said lens comprises a glass lens.