Optics: eye examining – vision testing and correcting – Spectacles and eyeglasses – Ophthalmic lenses or blanks
Reexamination Certificate
2001-07-06
2003-10-14
Sugarman, Scott J. (Department: 2873)
Optics: eye examining, vision testing and correcting
Spectacles and eyeglasses
Ophthalmic lenses or blanks
C351S159000
Reexamination Certificate
active
06631988
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to designing method, a manufacturing method of a spectacle lens to correct eyesight, and a spectacle lens series.
In general, a spectacle lens is custom-made to meet the customer's specification. However, it takes long time to process both front and back surfaces after receiving the customer's order. Therefore, semifinished lens blanks whose front surfaces are finished are stockpiled and a back surface of the selected semifinished lens blank is processed according to the customer's specification in order to shorten delivery times. Further, the entire range of available vertex power of a spectacle lens is divided into about ten sections, and one type of the semifinished lens blank is prepared for each of the sections.
Aspherical spectacle lenses whose at least one of the front and back surfaces is aspherical have come into wide use. When the spectacle lens employs an aspherical surface, the base curve becomes slower (i.e., the absolute value of the front vertex power decreases) and the maximum thickness becomes shorter as compared with a spherical lens whose both of the front and back surfaces are spherical. A conventional semifinished lens blank prepared for an aspherical spectacle lens has an aspherical finished front surface. A back surface thereof will be processed to be spherical or toric to meet the customer's specification.
FIGS. 17A through 17C
show a sample of the sections of the vertex power,
FIG. 17A
shows a range of minus diopter,
FIG. 17B
shows a range of plus diopter and
FIG. 17C
shows a range of mixed diopter. The entire range of the available vertex power, which is a combination of a spherical power SPH and a cylindrical power CYL, is divided into nine sections I through IX. Unit of each of powers is diopter and that is indicated by “D” in the following description. One type of the semifinished lens blank is prepared for each of the sections. The relationship between the sections and the base curves of the semifinished lens blank is shown in TABLE 1.
TABLE 1
Section
Base curve(D)
Section
Base curve(D)
I
0.50
VI
5.00
II
1.25
VII
6.00
III
2.00
VIII
7.00
IV
3.00
IX
8.00
V
4.00
—
—
FIG. 18
shows surface powers of the front surfaces D
1
m(h) (unit: diopter) of the semifinished lens blanks prepared for the respective sections I to IX at the point whose distance from the optical axis of said finished lens is h (unit: mm) in a plane that contains the optical axis.
The sections of the vertex power are determined such that optical performances of the finished lenses that have the same front surface shape fall in an allowable range for every vertex power within the specific section. For instance, in the section II, which covers SPH −5.25 D to −7.00 D and CYL 0.00 D to −2.00 D, the common aspherical surface whose base curve is 1.25 D is employed as the front surface and the back surface is processed to be a spherical surface whose surface power is −7.25 D when the required vertex power is SPH −6.00 D and CYL 0.00 D. Further, when the required vertex power is SPH −7.00 D and CYL −2.00 D, the back surface is processed to be a toric surface whose minimum and maximum surface powers are −8.25 D and −10.25 D, respectively.
According to the conventional designing and/or manufacturing method, when the required vertex power is at the center of each section, an optical performance of the spectacle lens can be kept high. However, when the required vertex power is in periphery of each section, the optical performance is degraded.
For example,
FIG. 19
shows graphs of astigmatisms with respect to the visual angle &bgr; of the spectacle lenses whose required vertex powers are SPH +3.25 D and +4.00 D that are in periphery of the section VIII. The section VXII covers SPH +3.25 D to +4.00 D and CYL 0.00 D to +2.00 D, the front surface of the semifinished lens blank prepared for this section is an aspherical surface whose base curve is +7.00 D. In each graph a solid line represents the astigmatism AS
∞
for infinite object distance and a dotted line represents the astigmatism AS
300
for object distance 300 mm. As shown in
FIG. 19
, the astigmatism AS
300
is significant for the spectacle lens whose vertex power is SPH +3.25, while the astigmatism AS
∞
is significant for the spectacle lens whose vertex power is SPH +4.00. Namely, the astigmatisms of the finished lenses (SPH +3.25 and SPH +4.00) are not balanced.
FIG. 20
shows average power error AP
∞
(
30
) at 30° of visual angle for infinite object distance, astigmatism AS
∞
(
30
) at 30° of visual angle for infinite object distance, and astigmatism AS
300
(
30
) at 30° of visual angle for the object distance 300 mm of the spectacle lens series designed and manufactured by the conventional method within the entire range of vertex power SPH −8.00 D to +5.00 D. As shown in
FIG. 20
, the aberrations significantly vary in each section and the degradations stand out at boundaries of the sections.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a design method and a manufacturing method, which are capable of designing and manufacturing a spectacle lens having good optical performance for every vertex power.
For the above object, according to the designing method of the present invention, the entire range of available vertex power of a spectacle lens is divided into a plurality of sections, at least one type of semifinished lens blank whose one of the front and back surfaces is finished is prepared for each of the sections, one type of the semifinished lens blank is selected according to a required specification, and then an aspherical shape design for processing the unfinished surface of the selected semifinished lens blank is determined to be optimized for the required specification. The specification includes the vertex power and so on.
With this method, since the aspherical shape design for processing the unfinished surface of the lens blank is determined based on the required specification, a degree of flexibility in surface design becomes higher than the conventional method (an unfinished back surface of a lens blank whose front surface is finished as an aspherical surface is processed as a spherical or totic surface), which increases the optical performance of the finished lens regardless of whether the required vertex power is in the periphery in the specific section or in the center thereof.
In the following description, the surface of the finished lens that corresponds to the finished surface of the semifinished lens blank is referred to as a common surface that is common in the same section and the other surface of the finished lens that corresponds to the unfinished surface of the semifinished lens blank is referred to as a custom surface that is custom-made according to the required specification.
Further, the aspherical shape of the custom surface is optimized such that any pair of the finished lenses that have different vertex powers within the same section preferably satisfy the following condition (1) for at least one height h within the range of 0<h<15:
&Dgr;
D
1
m
(
h
)
i
+&Dgr;D
2
m
(
h
)
i
≠&Dgr;D
1
m
(
h
)
j
+&Dgr;D
2
m
(
h
)
j
(1)
where
D
1
m(h) and D
2
m(h) are surface powers of the front and back surfaces (unit: diopter) at the point whose distance from the optical axis of said finished lens is h (unit: mm) in a plane that contains said optical axis,
&Dgr;D
1
m(h) is a variation of surface power of the front surface and is obtained by D
1
m(h)−D
1
m(
0
),
&Dgr;D
2
m(h) is a variation of surface power of the back surface and is obtained by D
2
m(h)−D
2
m(
0
), and
the subscripts “i” and “j” represent the values of the finished lenses that have different vertex powers within the same section.
The condition (1) means &Dgr;D
2
m(h)
i
≠&Dgr;D
2
m(h)
j
when the front surface is a common
Obara Yoshimi
Shirayanagi Moriyasu
Greenblum & Bernstein P.L.C.
Pentax Corporation
Sugarman Scott J.
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