Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1998-06-17
2002-03-12
Sugarman, Scott J. (Department: 2873)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
Reexamination Certificate
active
06356373
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a progressive power (multi-focal) lens for eyeglasses, in which the surface power continuously changes from a distance portion to a near portion. In particular, the present invention relates to a progressive power lens which is provided on a peripheral edge thereof with a rim surface portion whose width is reduced to provide an increased effective surface area of the lens. The present invention also relates to a mold which produce such a progressive power lens.
2. Description of Related Art
In a known process of producing a plastic lens for eyeglasses, a monomeric material
54
in liquid state is introduced and heated in a cavity defined between molds
51
,
52
and a gasket
53
to polymerize the same, so that a lens
50
of a solid polymer can be obtained, as shown in FIG.
16
.
The gasket
53
is made of a relatively elastically deformable material to confine the monomer
54
in the mold cavity defined between the molds
51
and
52
and to absorb a change in volume due to the polymerization from a monomer to a polymer.
The mold to produce a plastic single focal lens or a plastic multi-focus lens having a distance portion and a near portion separate from the distance portion, or a semi-product thereof, is usually provided with a spherical mold surface, and hence, the thickness T of the gasket
53
to be used is constant over the entire periphery of the lens. However, for a mold to produce an astigmatic power lens as a final product, a gasket whose thickness varies in accordance with a shape of a toric lens surface must be used. To reduce the number of kinds of gaskets to be prepared, the toric surfaces are systematized.
In the mold for the progressive power lens, the shape of the surface thereof on the progressive surface (progressive side) is a complex aspherical surface. Moreover, for example, in the arrangement of the mold and the gaskets as shown in
FIG. 16
, the thickness of the gaskets are not uniform. In particular, in a mold for the progressive power lens whose optical center is deviated from the center of the circle (diameter) of the lens, the change in the thickness of the gasket, along the outer periphery thereof, is much more complicated.
Assuming that, in coordinate systems as shown in
FIGS. 17 and 18
in which the diameters of the lens
50
and the molds
51
,
52
are indicated by
55
and
56
, respectively, and coordinates Z1 and Z2 (
FIG. 18
) of both surfaces of the lens
50
at an optional angle &thgr; are represented by the Z-axis, a graph as shown in
FIG. 19
is obtained. The distance between Z1 and Z2, at an optional angle &thgr;, corresponds to the thickness T of the gasket at the angle &thgr;.
A progressive power lens includes a base curve representing the power of the distance portion and the power of the near portion in combination (note that a difference between the power of the distance portion and the power of the near portion is referred to as “addition power”). There are more than 100 combinations of the base curve and the power of the near portion for one lens system (product). It is therefore impractical to prepare many gaskets corresponding to these combinations in view of the production cost or stocking thereof.
To this end, the mold
51
, which forms the progressive surface of the lens, is ground flat at the peripheral portion, so that the rim surface portion (flat surface portion or non-progressive focus area)
58
, which does not serve as a progressive surface (effective surface), is formed at the periphery of the lens, as shown in FIG.
20
. Consequently, the gasket has a uniform thickness regardless of the angle &thgr;.
Thus, the thickness T of the gasket is uniformly constant over the entire periphery of the lens as seen in
FIG. 21
, and the gasket can be commonly used with various kinds of progressive surfaces having different base curves and different addition powers in combination.
FIG. 22
shows a mold used to form the progressive surface (effective surface) of a progressive power lens, using the gasket having the rim surface
58
. As can be seen in
FIG. 22
, the rim surface
58
is formed around (on upper and lower sides of) the progressive surface (effective surface)
57
. The diameter of the effective progressive surface
57
is reduced in the vertical direction due to the presence of the rim surface portion
58
, but no serious problem is practically caused by the reduction of the effective diameter as, in general, the diameter of a frame for eyeglasses in the vertical direction is smaller than the diameter thereof in the horizontal direction.
However, to respond to the requirement to make the eyeglasses thinner and lighter, the radius of the base curve of the progressive power lens has recently been increased. In particular, in the lens having a large negative power, if the flat rim surface
58
is provided, the reduction of the effective diameter in the vertical direction is not acceptable.
FIG. 23
shows an example of a known progressive power lens which is used to correct a highly myopic presbyopia, wherein the addition power is about 3.00 D (diopter), and the surface power of the distance portion is around −7.00 D to −10.00 D (diopter). The effective progressive surface spreads over the whole lens diameter (=70 &PHgr;mm) in the horizontal direction, but is reduced in the vertical direction by the rim surface portions
58
each having a width of 8.2 mm, which are formed on the upper and lower sides of the progressive surface
57
. The average surface power at the distance reference point
59
is 0.12 D and the refractive index of the blank material is 1.6. The distance reference point refers to a point on the front surface of the lens at which the corrective power for the distance portion shall apply.
FIG. 25
shows vertical and horizontal sections
60
and
61
which define the progressive surface portion
57
of a progressive power lens in an overlapped state. For clarity, in the drawings, the dimension in the longitudinal direction, only, is enlarged. The vertical and horizontal section lines of the rim surface
58
are indicated by dotted and dashed lines. The intersecting points of the progressive surface and the rim surface in the vertical section are indicated at
64
and
64
′, and the corresponding intersecting points in the horizontal section are indicated by
65
and
65
′, respectively. The symbol &phgr; designates the angle defined by lines normal to the rim surface and the progressive surface. The parenthesized numerals represent the angle &thgr; in FIG.
17
. “Wa” designates the width of the upper rim surface portion, and “Wb” the width of the lower rim surface portion, respectively. The progressive surface is inclined at an appropriate angle so that the width Wa is identical to the width Wb.
FIG. 24
shows another example of a known progressive power lens which is used to correct a myopic presbyopia, wherein the addition power is about 3.00 D (diopter), and the surface power of the distance portion is around −3.00 D to −6.00 D (diopter). The effective progressive surface spreads over the whole lens diameter (=75 &PHgr;mm) in the horizontal direction but is reduced in the vertical direction by the rim surface portions
58
each having a width of 4.1 mm, which are formed on the upper and lower sides of the progressive surface
57
. The average surface power at the distance reference point
59
is 2.04 D and the refractive index of the blank material is 1.6.
FIG. 26
, which corresponds to
FIG. 25
, shows vertical and horizontal sections
60
and
61
which define the progressive surface portion
57
of a progressive power lens in an overlapped state.
FIGS. 25 and 26
show that the widths Wa and Wb of the upper and lower rim surface portions increase as the curvature of the base curve decreases, so long as the addition power is identical.
In the first example of a known progressive power lens, in which the curvature of the base curve is small, the angle &phgr;, defin
Asahi Kogaku Kogyo Kabushiki Kaisha
Greenblum & Bernstein P.L.C.
Sugarman Scott J.
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