Optics: eye examining – vision testing and correcting – Spectacles and eyeglasses – Ophthalmic lenses or blanks
Patent
1998-06-04
1999-12-28
Manuel, George
Optics: eye examining, vision testing and correcting
Spectacles and eyeglasses
Ophthalmic lenses or blanks
G02C 704
Patent
active
060072016
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of The Invention
The present invention relates generally to a multifocal contact lens, a mold for forming the same, and a method for producing the same. More specifically, the invention relates to a multifocal contact lens with a lens curve formed by alternately arranging a plurality of curved surfaces for far vision and a plurality of curved surface for near vision in the form of concentric zones, a die for forming the same, a method for manufacturing the die, and a method for producing the multifocal contact lens.
2. Description of The Prior Art
A multifocal contact lens, wherein a plurality of portions for far vision and a plurality of portions for near vision are altermately arranged in the form of concentric zones, has been proposed in, e.g., Japanese Patent Laid-Open No. 59-146020. When a user wears such a contact lens, the user can consciously choose one of far and near ranges which can be simultaneously viewed by the user. This contact lens is useful since the user can naturally and smoothly choose one of the far and near ranges.
As shown in FIG. 8, such a contact lens 1 has a front curve 2 formed by altermately arranging a plurality of curved surfaces F1, F2, . . . for far vision and a plurality of curved surfaces N1, N2, . . . for near vision in the form of concentric zones, and a base curve 3 having a shape corresponding to the curved surface of the user's cornea.
In conventional contact lenses, the curved surfaces F1, F2, . . . for far vision and the curved surfaces N1, N2, . . . for near vision are formed on the front curve 2 as follows.
It is assumed that the radius of curvature of the curved surface for far vision is R.sub.F and the radius of curvature of the curved surface for near vision is R.sub.N. First, a circle having a radius R.sub.F from a point P on an optical axis corresponding to Z-axis is described to derive an intersection point with the optical axis. It is assumed that this intersection point is a center O.sub.F1 of curvature of the curved surface F1 for far vision. Then, a circle having the radius R.sub.F is described about the center O.sub.F1 of curvature to derive an intersection point P.sub.F1 with a straight line l.sub.F1 which defines a predetermined zone width of the curved surface F1 for far vision and which is parallel to the optical axis. Then, a circle having the radius R.sub.N is described about the point P.sub.F1 to derive an intersection point with the optical axis. In is assumed that this intersection point is a center O.sub.N1 of curvature of the curved surface N1 for near vision. Then, a circle having the radius R.sub.N is described about the center O.sub.N1 of curvature to derive an intersection point P.sub.N1 with a straight line l.sub.N1 defining a predetermined zone width of the curved surface N1 for near vision.
Similarly, a circle having the radius R.sub.F is described about the point P.sub.N1 to derive an intersection point with the optical axis. It is assumed that this intersection point is a center O.sub.F2 of curvature of the curved surface F2 for far vision. Then, a circle having the radius R.sub.F is described about the center O.sub.F2 of curvature to derive an intersection point P.sub.F2 with a straight line l.sub.F2 which defines a predetermined zone width of the curved surface F2 for far vision and which is parallel to the optical axis. Then, a circle having the radius R.sub.N is described about the point P.sub.F2 to derive an intersection point with the optical axis. It is assumed that this intersection point is a center O.sub.N2 of curvature of the curved surface N2 for near vision.
The centers O.sub.F1, O.sub.F2, . . . of curvature of the curved surfaces F1, F2, . . . for far vision and the centers O.sub.N1, O.sub.N2, . . . of curvature of the curved surfaces N1, N2, . . . for near vision thus obtained are shown in FIG. 7.
As can be clearly seen from FIG. 7, the centers O.sub.F1, O.sub.F2, . . . of curvature of the curved surfaces F1, F2, . . . for far vision are distributed so as to be sequentially shifte
REFERENCES:
patent: 4704016 (1987-11-01), De Carle
patent: 5541678 (1996-07-01), Awanohara et al.
patent: 5619289 (1997-04-01), Seidner et al.
Awanohara Yoshinori
Komatu Akira
Shinohara Toshihide
Wada Osamu
Yokoyama Osamu
Manuel George
Seiko Epson Corporation
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