Spectacle Lens and Method for Designing the Same
A spectacle lens includes: a near region corresponding to near vision, wherein a spherical equivalent power at a point located on a principal line of fixation in the near region is larger than the spherical equivalent power in a region away from the point toward the nose, in a horizontal direction with reference to a spectacle wearer but smaller than the spherical equivalent power in a region away from the point toward the ear in the horizontal direction.
1 . A spectacle lens comprising:
a near region corresponding to near vision,
wherein a spherical equivalent power at a point located on a principal line of fixation in the near region is larger than the spherical equivalent power in a region away from the point toward the nose in a horizontal direction with reference to a spectacle wearer but smaller than the spherical equivalent power in a region away from the point toward the ear in the horizontal direction.
2 . The spectacle lens according to claim 1 , further comprising: in addition to the near region,
a far region corresponding to far vision and having power smaller than the power in the near region; and
an intermediate region corresponding to intermediate vision and having power continuously changing from the power in the far region to the power in the near region.
3 . The spectacle lens according to claim 1 , further comprising: in addition to the near region,
an intermediate region corresponding to intermediate vision and having power smaller than the power in the near region.
4 . The spectacle lens according to claim 2 ,
wherein the point is a progressing endpoint positioned at the boundary between the near region and the intermediate region or a near dioptric power measuring point, which is the center of the near region.
5 . The spectacle lens according to claim 2 ,
wherein the gradient fn(x) of the spherical equivalent power along a line passing through the point and extending in the horizontal direction is defined within a range where astigmatism is smaller than or equal to 0.5 diopter (D) by the following Equation (1):
fn
(
x
)
=
x
[
1
L
2
+
(
Lx
/
l
)
2
]
(
1
)
where x represents the coordinate of the horizontal line, an x coordinate of zero corresponds to the position of the foot of a line extending from the portion of the principal line of fixation that corresponds to the far region and intersecting the horizontal line at right angles, L represents a near working distance, and l represents the distance from the pivotal center of the eyeball to the back surface of the lens.
6 . The spectacle lens according to claim 3 ,
wherein the position of a fitting point of the spectacle lens when worn is determined by a near interpupillary distance,
the point is the fitting point, and
the gradient fn(x) of the spherical equivalent power along a line extending in the horizontal direction is defined within a range where astigmatism is smaller than or equal to 0.5 diopter (D) by the following Equation (2):
fn
(
x
)
=
x
[
1
L
2
+
[
L
(
x
-
m
)
l
]
2
]
(
2
)
where x represents the coordinate of the line extending in the horizontal direction, the positive side of the x coordinate axis corresponds to the ear side in the horizontal direction, an x coordinate of zero corresponds to the fitting point, L represents a near working distance, l represents the distance from the pivotal center of the eyeball to the back surface of the lens, and m represents the difference between a far monocular interpupillary distance and a near monocular interpupillary distance.
7 . A method for designing the spectacle lens according to claim 1 , the method comprising:
setting the principal line of fixation;
setting the spherical equivalent power at the point in the near region;
setting the spherical equivalent power at the point to be larger than the spherical equivalent power in a region away from the point toward the nose in the horizontal direction with reference to the spectacle wearer; and
setting the spherical equivalent power at the point to be smaller than the spherical equivalent power in a region away from the principal line of fixation toward the ear in the horizontal direction.