Optics: eye examining – vision testing and correcting – Spectacles and eyeglasses – Ophthalmic lenses or blanks
Reexamination Certificate
2002-08-09
2004-08-17
Epps, Georgia (Department: 2873)
Optics: eye examining, vision testing and correcting
Spectacles and eyeglasses
Ophthalmic lenses or blanks
C351S177000
Reexamination Certificate
active
06776486
ABSTRACT:
This application claims priority from international application number PCT/GB02/02284 filed on May 31, 2002, the contents of which are hereby incorporated by reference in their entirety. This international application will be published under PCT Article 21(2) in English.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates generally to progressive addition power ophthalmic lenses and, in particular, to an improved system and method for designing such lenses.
2. Description of the Related Art
Bifocal spectacle lenses have been used for many years by people suffering from presbyopia, a medical condition that causes loss of accommodation of the eye with advancing age resulting in difficulty focusing. Bifocal lenses provided a solution by dividing the lenses horizontally into two regions, each having a different optical power. The upper region of the lens was designed with the appropriate optical power for distance viewing, while the lower region was designed for closer viewing (e.g. reading). This allows the wearer to focus at different distances by merely changing their gaze position. However, wearers frequently experienced discomfort due to the abrupt transition between the different lens regions. As a consequence, progressive addition lenses were developed to provide a smooth transition in optical power between the regions of the lens.
Conventionally, progressive addition lenses are usually described as having three zones: an upper zone for far vision, a lower zone for near vision, and an intermediate progression corridor that bridges the first two zones.
FIG. 1
is a diagram of a typical progressive lens shown in vertical elevation (plan view). The lens has an distance zone
2
with a given, relatively lower mean power and a reading zone
4
with relatively higher mean power. An intermediate progression corridor
6
of varying and usually increasing mean power connects the distance and reading zones. The outlying regions
8
adjoining the progression corridor and the lens boundary
10
(i.e. the edge of the lens) are also shown.
The goals in designing progressive lenses have been to provide both essentially clear vision in upper and lower zones
2
and
4
and smooth variation in optical power through the progression corridor
6
, while at the same time to control the distribution of astigmatism and other optical aberrations.
Early design techniques required the lens to be spherical throughout the distance and reading zones, and employed various interpolative methods to determine the lens shape in the progression corridor and outlying regions. These techniques suffered from several disadvantages. Although the optical properties of the distance zone, reading zone, and progression corridor were usually satisfactory, regions adjoining the progression corridor and lens edge tended to have significant astigmatism. Interpolative methods designed to compress astigmatism into regions near the progression corridor yielded relatively steep gradients in mean power, astigmatism and prism. The resulting visual field was not as smooth and continuous as would be desirable for comfort, ease of focusing, and maximizing the effective usable area of the lens.
FIG. 2
shows a three dimensional representation of the mean power distribution over the surface of a typical progressive lens design. Mean power M is graphed in the vertical direction and the disc of the lens in shown against x and y coordinates. The disc of the lens is viewed from an angle less than 90° above the plane of the lens. The orientation of the lens is opposite of that in
FIG. 1
, the distance area with low mean power
12
shown in the foreground of FIG.
2
and the reading area with high mean power
14
shown at the back. Steep gradients in mean power are evident, especially in the outlying regions
16
.
Many progressive lens design systems permit the designer to set optical properties at only a few isolated points, curves, or zones of the lens and employ a variety of interpolative methods to determine the shape and optical properties of the remainder of the lens.
U.S. Pat. No. 3,687,528 to Maitenaz, for example, describes a technique in which the designer specifies the shape and optical properties of a base curve running from the upper part of the lens to its lower part. The base curve, or “meridian line” is the intersection of the lens surface with the principal vertical meridian, a plane dividing the lens into two symmetrical halves. The designer is constrained by the requirement that astigmatism vanish everywhere along the meridian line (i.e. the meridian line must be “umbilical”). Maitenaz discloses several explicit formulas for extrapolating the shape of the lens horizontally from an umbilical meridian.
U.S. Pat. No. 4,315,673 to Guilino describes a method in which mean power is specified along an umbilical meridian and provides an explicit formula for extrapolating the shape of the remainder of the lens.
In a Jul. 20, 1982 essay, “The TRUVISION® Progressive Power Lens,” J. T. Winthrop describes a progressive lens design method in which the distance and reading zones are spherical. The design method described includes specifying mean power on the perimeters of the distance and reading zones, which are treated as the only boundaries.
U.S. Pat. No. 4,514,061 to Winthrop also describes a design system in which the distance and reading areas are spherical. The designer specifies mean power in the distance and reading areas, as well as along an umbilical meridian connecting the two areas. The shape of the remainder of the lens is determined by extrapolation along a set of level surfaces of a solution of the Laplace equation subject to boundary conditions at the distance and reading areas but not at the edge of the lens. The lens designer cannot specify lens height directly at the edge of the lens.
U.S. Pat. No. 4,861,153 to Winthrop also describes a system in which the designer specifies mean power along an umbilical meridian. Again, the shape of the remainder of the lens is determined by extrapolation along a set of level surfaces of a solution of the Laplace equation that intersect the umbilical meridian. No means is provided for the lens designer to specify lens height directly at the edge of the lens.
U.S. Pat. No. 4,606,622 to Furter and G. Furter, “Zeiss Gradal HS—The progressive addition lens with maximum wearing comfort”, Zeiss Information 97, 55-59, 1986, describe a method in which the lens designer specifies the mean power of the lens at a number of special points in the progression corridor. The full surface shape is then extrapolated using splines. The designer adjusts the mean power at the special points in order to improve the overall properties of the generated surface.
U.S. Pat. No. 5,886,766 to Kaga et al. describes a method in which the lens designer supplies only the “concept of the lens.” The design concept includes specifications such as the mean power in the distance zone, the addition power, and an overall approximate shape of the lens surface. Rather than being specified directly by the designer, the distribution of mean power over the remainder of the lens surface is subsequently calculated.
U.S. Pat. No. 4,838,675 to Barkan et al. describes a method for improving a progressive lens whose shape has already been roughly described by a base surface function. An improved progressive lens is calculated by selecting a function defined over some subregion of the lens, where the selected function is to be added to the base surface function. The selected function is chosen from a family of functions interrelated by one or a few parameters; and the optimal selection is made by extremizing the value of a predefined measure of merit.
In a system described by J. Loos, G. Greiner and H. P. Seidel, “A variational approach to progressive lens design”, Computer Aided Design 30, 595-602, 1998 and by M. Tazeroualti, “Designing a progressive lens”, in the book edited by P. J. Laurent et al., Curves and Surfaces in Geometric Design, A K Peters, 1994, pp. 467-474, the lens surface is defined by a
McLoughlin Hugh
Payne Derek
Steele Trevor
Crossbows Optical Limited
Epps Georgia
Ice Miller
Powlick Jill T.
Raizen Deborah
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