Optics: eye examining – vision testing and correcting – Spectacles and eyeglasses – Ophthalmic lenses or blanks
Reexamination Certificate
2001-10-16
2004-09-14
Dang, Hung Xuan (Department: 2873)
Optics: eye examining, vision testing and correcting
Spectacles and eyeglasses
Ophthalmic lenses or blanks
C351S169000, C351S170000
Reexamination Certificate
active
06789895
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a single-vision spectacle lens to correct eyesight and particularly, to an aspherical lens having a prismatic power to correct heteophoria (more conventionally known as heterophoria) of an eye.
A spectacle lens for correcting heteophoria (visual axes are deviated during a resting period) has a prismatic power. A conventional aspherical lens produces the prismatic power by tilting a back surface (an eye side) with respect to a front surface (an object side).
FIGS. 113 and 114
show an example of a conventional spectacle lens having a prismatic power;
FIG. 113
is a sectional view and
FIG. 114
is a plan view from the front surface. A spectacle lens
21
has a rotationally-symmetrical aspherical front surface
22
and a spherical back surface
23
. A framing reference point
24
is defined to be coincident with a pupil of an eye
5
of a user when the spectacle lens
21
is installed on a frame. In the drawings, a z
1
-axis is defined to be coincident with a normal to the front surface
22
at the frame reference point
24
, and x
1
- and y
1
-axes, which intersect at right angle, are defined in a plane that contacts with the front surface
22
and is perpendicular to the z
1
-axis. The y
1
-axis is direction from the base to the apex of the prism and the x
1
-axis is perpendicular to both of the y
1
- and z
1
-axes in a left-hand coordinate system.
The front surface
22
does not tilt with respect to the x
1
-y
1
plane, while the back surface
23
tilts with respect to the x
1
-y
1
plane. As a result, the spectacle lens
21
has a prismatic power whose base setting is the minus direction of the y
1
-axis.
However, since the above-described conventional spectacle lens is designed through the use of the front surface
22
and the back surface
23
that are originally designed for a lens having no prismatic power and it produces the prismatic power by tilting the front and back surfaces with respect to each other, although it can correct hereophoria, aberration caused by adding the prismatic power is not taken into consideration.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an aspherical spectacle lens, which is capable of having a sufficient optical performance even if the lens has a prismatic power to correct hereophoria of an eye.
For the above object, the present invention is characterized in that aberration caused by adding a prismatic power is corrected by a rotationally-asymmetrical surface. The aberration caused by adding the prismatic power is rotationally-asymmetrical and therefore, it is difficult to correct the aberration with a rotationally-symmetrical surface. According to the present invention, one of front and back surfaces is formed as a rotationally-asymmetrical aspherical surface, which can correct the aberration caused by adding the prismatic power.
In the case when the back surface is rotationally-asymmetrical, it is preferable that curvature of an intersection line of a plane containing the normal to the rotationally-asymmetrical surface at a framing reference point and the rotationally-asymmetrical surface at the prism base side is larger than that at the apex side. The framing reference point is coincident with a pupil position of a user when the spectacle lens is installed on a frame, and is coincident with a prism reference point for a lens having a prismatic power. On the other hand, when the front surface is rotationally-asymmetrical, it is desirable that the curvature of the intersection line at the prism base side is smaller than that at the apex side.
In more detail, the following condition (1) is preferably satisfied within the ranges of 10≦h≦20 and 30≦&thgr;≦150;
C
2−1
(
h, &thgr;+
180)−
C
2−1
(
h
, &thgr;)>0 (1)
where
C
2−1
(h, &thgr;)=C
2
(h, &thgr;)−C
1
(h, &thgr;);
C
1
(h, &thgr;) is curvature of an intersection line of a plane, which contains a z
1
-axis and forms angle &thgr; (degree) with respect to an x
1
-axis, and the front surface at a point whose distance from a z
1
-axis is h (mm);
C
2
(h, &thgr;) is curvature of an intersection line of a plane, which contains a z
2
-axis and forms angle &thgr; (degree) with respect to an x
2
-axis, and the back surface at a point whose distance from a z
2
-axis is h (mm);
z
1
-axis is a normal to the front surface at the framing reference point;
y
1
-axis is direction from the base to the apex in a plane perpendicular to the z
1
-axis;
x
1
-axis is perpendicular to both of the y
1
- and z
1
-axes in a left-hand coordinate system;
z
2
-axis is a normal to the back surface at the framing reference point;
y
2
-axis is direction from the base to the apex in a plane perpendicular to the z
2
-axis; and
x
2
-axis is perpendicular to both of the y
2
- and z
2
-axes in a left-hand coordinate system.
Further, it is preferable that the condition (2) is satisfied when the back surface is rotationally-asymmetrical and that the condition (3) is satisfied when the front surface is rotationally-asymmetrical;
C
2
(
h, &thgr;+
180)−
C
2
(
h
, &thgr;)>0 (2)
C
1
(
h, &thgr;+
180)−
C
1
(
h
, &thgr;)<0 (3)
Further, in order to respond to various combinations of spherical power, cylindrical power, cylindrical axis direction, prismatic power and base setting, it is desirable that 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.
REFERENCES:
patent: 5050979 (1991-09-01), Shinohara
patent: 5050980 (1991-09-01), Shinohara
patent: 5353072 (1994-10-01), Tejima et al.
patent: 5550600 (1996-08-01), Ueno
patent: 5610670 (1997-03-01), Ueno
patent: 6056401 (2000-05-01), Shirayanagi
patent: 6089713 (2000-07-01), Hof et al.
patent: 371460 (1990-06-01), None
patent: 97/23804 (1997-07-01), None
patent: 99/04307 (1999-01-01), None
Dang Hung Xuan
Greenblum & Bernstein P.L.C.
PENTAX Corporation
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