Optics: eye examining – vision testing and correcting – Spectacles and eyeglasses – Ophthalmic lenses or blanks
Reexamination Certificate
2002-10-11
2003-11-25
Sugarman, Scott J. (Department: 2873)
Optics: eye examining, vision testing and correcting
Spectacles and eyeglasses
Ophthalmic lenses or blanks
C351S175000
Reexamination Certificate
active
06652097
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a progressive-power spectacle lens to correct eyesight, and particularly, to a progressive-power lens having a prismatic power to correct heterophoria of an eye.
A progressive-power spectacle lens has a front surface (an object side) and a back surface (an eye side), and at least one of the surfaces is configured as a progressive-power surface whose dioptric power varies depending on the position thereon.
FIG. 59
is a plan view showing one example of a progressive-power surface
2
of a conventional progressive-power lens
1
. The progressive-power lens
1
includes a distance portion
3
having a dioptric power for distance vision at an upper area of the lens, a near portion
4
having a dioptric power for near vision at a lower area of the lens, and an intermediate portion
5
having a progressive dioptric power changing between the distance portion
3
and the near portion
4
. A fitting point E that is a reference point with respect to a position of a user's eye when the lens is installed in a frame, a distance reference point F, a near reference point N and a prism reference point PR for measuring dioptric powers are defined on the progressive-power surface
2
.
Since the curvature of the progressive-power surface
2
gradually increases or decreases from the upper side to the lower side within the intermediate portion, the thickness of the upper edge is different from that of the lower edge when the front and back surfaces are arranged to be perpendicular to a common normal at the center thereof.
FIG. 60A
is a cross sectional side view of a progressive-power lens that is designed such that the front and back surfaces are perpendicular to a common axis at the center thereof. In this example, the lens of
FIG. 60A
has a plus distance dioptric power and the front surface thereof is formed as a progressive-power surface. As shown in
FIG. 60A
, the entire lens becomes exceedingly thick to keep a necessary thickness at the lower edge, which increases the weight of the lens. In order to reduce the thickness and weight of the lens, a method known as “prism thinning” for relatively tilting the front and back surfaces to uniform the thickness at both upper and lower edges as shown in
FIG. 60B
is generally employed. This method introduces unprescribed prism effect in the lens.
FIG. 61A
is across sectional view of another example of a conventional progressive-power spectacle lens, having a minus distance dioptric power. In this example, a front surface is formed as a progressive-power surface that is designed such that the front and back surfaces are perpendicular to a common axis at the center thereof. As shown in
FIG. 61A
, the thickness of the upper edge and the lower edge are unbalanced. Application of the prism thinning to the lens balances the thickness as shown in
FIG. 61B
, however, an unprescribed prism effect is introduced. It should be noted that wedge marks indicated in the lenses of
FIGS. 60B and 61B
show the unprescribed prism effect introduced by the prism thinning and the like.
Conventional progressive-power spectacle lenses are designed to include the unprescribed prism effect in order to reduce the thickness/weight and/or improve appearance. Specifically, the conventional progressive-power spectacle lenses are designed such that aberrations are well reduced with the above-described prism effect being introduced. An example of such a conventional progressive-power spectacle lens will be described.
The exemplary conventional progressive-power spectacle lens is designed for a right eye and has a progressive-power front surface and a spherical back surface. The spherical dioptric power is 0.00 diopter (referred to as “D” hereinafter), the addition power is 2.00D, the center thickness is 2.53 mm, the outer diameter is 80 mm and the refractive index is 1.60. The unprescribed prismatic effect, whose prismatic power is 1.47 prism-diopter (referred to as &Dgr; hereinafter) and whose prism base setting is 270°, is introduced to thin the lens and to uniform the edge thickness.
FIGS. 62A and 62B
show a coordinate system for illustrating performance of the progressive-power surface. The coordinate system is a left-hand orthogonal x-y-z coordinate system. The z-axis is a normal to the progressive-power surface at the prism reference point PR that is the origin of the coordinate system. The y-axis is perpendicular to the z-axis and is a vertical axis when the lens is installed in a frame. The x-axis is perpendicular to both the z-axis and the y-axis and is a horizontal axis when the lens is installed in a frame. A curvature at a point at a distance h (unit: mm) from the z-axis on an intersection line of the progressive-power surface and a plane that includes the z-axis and forms an angle &thgr; (unit: degrees) with the x-axis is expressed as a function C (h, &thgr;) (unit: D). A surface power D(h, &thgr;) (unit: D) at the point (h, &thgr;) is defined by a function D(h, &thgr;)=(n′−n)C(h, &thgr;). Reference n denotes a refractive index of medium on an object side with respect to the progressive-power surface, and n′ is a refractive index of medium on an eye side with respect to the progressive-power surface.
Table shown in
FIG. 63
indicates distribution of the surface power D(h, &thgr;) of the progressive-power surface of the conventional lens at a point indicated by the polar coordinate (h, &thgr;), i.e., at a point indicated by a distance h (mm) from the prism reference point PR and an angle &thgr; (degree) with respect to the x-axis. Further,
FIG. 64
is a graph showing relationships between the surface powers D(h, &thgr;) and the angle &thgr; for the distances h=10 mm, 15 mm, 20 mm and 25 mm, respectively. The surface power is relatively low in the distance portion within 30≦&thgr;≦150 and relatively high in the near portion within 240 ≦&thgr;≦300.
FIGS. 65 and 66
are three-dimension graphs showing transmitting optical performances of the conventional progressive-power spectacle lens.
FIG. 65
shows a mean refractive power error and
FIG. 66
shows astigmatism. In the graphs, plane coordinates represent angles of visual axis (unit: degree) in the vertical and horizontal directions, respectively, and the vertical axis of the graphs represents amount of aberration (unit: D).
A progressive-power spectacle lens for correcting heterophoria (Symptom: visual axes are deviated during a resting period) requires a prismatic effect for correcting heterophoria based on a prescription in addition to the unprescribed prismatic effect introduced by the prism thinning.
FIG. 67
is a horizontal cross sectional view of a lens that is designed by adding the prescribed prismatic effect for correcting heterophoria to the above-described conventional progressive-power spectacle lens. The front and back surfaces of the spectacle lens are relatively tilted to provide a necessary prism effect.
The above-described conventional progressive-power spectacle lens is designed such that front and back surfaces-originally designed for a lens having no prescribed prismatic effect are tilted with respect to each other to produce the desired prismatic effect. Therefore, although heterophoria can be corrected, aberration caused by the prescribed prismatic effect is not taken into consideration.
For instance, when the prismatic effect for correcting heterophoria whose prismatic power is 3.00 &Dgr; and prism base setting is 180° is introduced to the conventional progressive-power spectacle lens, the mean refractive power error and the astigmatism vary as shown in
FIGS. 68 and 69
, respectively. The mean refractive power error increases at the ear side in the distance portion, the astigmatism increases at the upper portion of the ear side and the nose side in the distance portion, and the balance of the aberrations between the ear side and the nose side is lost across the entire area.
SUMMARY OF THE INVENTION
The present invention is advantageous in that there is provided a progressive-p
Greenblum & Bernstein P.L.C.
Pentax Corporation
Sugarman Scott J.
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