Optics: eye examining – vision testing and correcting – Spectacles and eyeglasses – Ophthalmic lenses or blanks
Reexamination Certificate
2002-10-25
2004-12-21
Sugarman, Scott J. (Department: 2873)
Optics: eye examining, vision testing and correcting
Spectacles and eyeglasses
Ophthalmic lenses or blanks
C351S177000
Reexamination Certificate
active
06832834
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a method for computing a progressive spectacle lens, and also to a method for manufacturing a spectacle lens of this kind, drop plate kind molds, casting molds for casting, or molding plugs for press-forming spectacle lenses of this kind from a plastics material.
Progressive spectacle lenses (also called varifocal lenses, multifocal lenses etc.) are usually understood to be spectacle lenses having a different (smaller) power in the region through which a spectacles wearer views an object located at a great distance—hereunder designated as a distance portion—than in the region (near portion) through which the spectacles wearer views a near object. Located between the distance portion and the near portion is the so-called progressive zone in which the power of the spectacle lens continuously increases from that of the distance portion to that of the near portion. The magnitude of the power increase is also designated as addition power.
As a rule, the distance portion is located in the upper part of the spectacle lens and designed for viewing “to infinity”, whilst the near portion is located in the lower region and is particularly designed for reading. In spectacles for special applications—those for pilots or for monitor work stations are mentioned as examples—the distance and near portions may also be arranged differently and/or designed for other distances. Furthermore, it is possible for a plurality of near portions and/or distance portions and suitable progressive zones to be present.
With progressive spectacle lenses having a constant refractive index it is necessary, for the power to increase between the distance portion and the near portion, that the curvature of one or both surfaces continuously change from the distance portion to the near portion.
The surfaces of spectacle lenses are usually characterized by the so-called principal radii of curvature R1 and R2 at every point on the surface. (Sometimes also the principal curvatures K
1
=1/R1 and K
2
=1/R2 are given instead of the principal radii of curvature.) Together with the refractive index of the glass material, the principal radii of curvature govern the parameters frequently used for an ophthalmologic characterization of a surface:
Surface power=0.5·(
n−
1)·(1
/R
1+1/
R
2)
Surface astigmatism=(
n−
1)·(1/
R
1−1
/R
2).
Surface power is the parameter via which an increase of power from the distance portion to the near portion is achieved. Surface astigmatism (more clearly termed cylinder power) is a “troublesome property”, because an astigmatism—inasmuch as an eye does not have an innate astigmatism to be corrected—which exceeds a value of about 0.5 dpt results in an indistinctly seen image on the retina.
BACKGROUND OF THE INVENTION
Although any change of the curvature of the surface which is needed to achieve a surface power increase without vision being “disturbed” by surface astigmatism can be attained relatively simply along a (plane or curved) line, considerable “intersections” of surfaces will result alongside this line, leading to a large surface astigmatism which more or less impairs the lens in regions alongside the mentioned line. According to Minkwitz' Law, for a line lying in a plane and designed as a umbilical line, the surface astigmatism in the direction perpendicular to the umbilical line increases with a gradient which is twice that of the surface power along the umbilical line, so that, particularly in the progressive zone, disturbing values of the surface astigmatism already result close to the umbilical line. (A line which at every point has the same principal curvatures, i.e. is free of surface astigmatism, is termed a navel line or umbilical lime or ombilical line).
For this reason, the designing of a progressive spectacle lens surface contributing to power change has in the past started out from a line lying in a plane or extending in a sinuous manner—also termed a principal meridian or a principal line—which runs centrally along the surface from top to bottom, and approximately follows the principal viewing line. A principal viewing line is understood to be a series of points of penetration of the rays of sight directed through the spectacle lens surface onto objects located at different distances centrally in front of the nose during a movement, in particular a lowering, of the glance. The principal curvatures of each point of this line were chosen in such manner that the desired increase of the surface power from the distance portion to the near portion is achieved. Setting out from this line, (more or less) suitable computations were then made of the lateral regions of the surface using various methods or approaches.
In case of a planar principal line (i.e. principal meridian), the spectacle lens, when being fitted into a spectacle frame, is usually tilted by about 8° to 10°, so that the principal meridian extends obliquely from top to bottom in correspondence with the convergence of the eyes. Progressive spectacle lenses having a planar principal meridian are described, for example in U.S. Pat. No. 2,878,721 or DE-AS 20 44 639.
Attention is expressly drawn to these publications—as well as to all publications mentioned in the following—concerning all remaining terms not described here in greater detail.
Because the principal viewing line on a spectacle lens surface is not a straight or planar line, the use of a planar principal meridian always represents a compromise. For this reason it has been suggested for a long time that a sinuous line—also designated as a principal line—be used as a “construction backbone” for a progressive surface, the course of which follows, as well as possible, the actual course of the principal viewing line as determined by physiology, and not by the structure (!) of the spectacle lens.
Progressive spectacle lenses having a sinuous principal line have been described in many patent publications.
Attention drawn to U.S. Pat. No. 4,606,622 only as an example. In this publication, however, no details can be found of how the course of the principal line can be made “to coincide” with the principal viewing line.
Although various other publications are concerned with the course of the principal line, the approaches made therein are unsatisfactory—as will be set out in the following:
For the surfaces described in DE-C-42 38 067 and DE-C-43 42 234 the course of the principal line is composed of straight sections; in this, the angles between the straight lines vary in dependence on the addition power. To compose the principal line from straight sections is an unsuitable approach, because the principal line must be twice differentiable. To vary the principal line in dependence only on the addition power, in order to bring it into coincidence with the principal viewing line, is also unsatisfactory, because the principal viewing line depends on many other parameters. Furthermore, in these publications no method is given of how a progressive surface may be designed around this principal line to have properties as specified along the principal line.
The European Patent Application 88 307 917 describes that the course of the principal line should be varied in dependence on—and only on—the addition power. Apart from this, the course of the principal line is stipulated, presumably in the expectation that it will coincide with the principal viewing line.
In DE-A-196 12 284, in which the distinction made in the present application between principal line (construction line of at least one surface of the spectacle lens) and principal viewing line (physiological property) is not made, and which instead mentions only a principal viewing line (which, after all, is a property of the spectacle lens), a spectacle lens is described having a principal line—or more precisely stated, an offset principal line—which varies in dependence on the power of the distance portion (stronger principal meridian) and the addition power. Whether a principal line of this kind coincides with the actua
Altheimer Helmut
Esser Gregor
Haimerl Walter
Pfeiffer Herbert
Crowell & Moring LLP
Rodenstock GmbH
Sugarman Scott J.
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