Toric contact lens with improved posterior surface design
View Patent ↗Ophthalmic lenses for correcting astigmatism having a posterior surface with a central optic zone, a peripheral zone, and a blending zone therebetween. The surface of the central zone may be asphero-toric and the surface of the peripheral zone aspheric, with these flatter slopes smoothening out the transition between the central and peripheral zones. The blending zone gradually transitions the curvatures of the central and peripheral zones to further smoothen out the central-to-peripheral-zone transition.
1. An ophthalmic lens, comprising:
a posterior surface having a central optic zone, a peripheral zone, and a blending zone therebetween;
the central zone being asphero-toric and defined by the equation:
z
=
(
cx
)
(
x
2
)
+
(
cy
)
(
y
2
)
1
+
1
-
(
1
+
kx
)
(
cx
2
)
(
x
2
)
-
(
1
+
ky
)
(
cy
2
)
(
y
2
)
where z, x, and y are coordinates relative to respective z-, x-, and y-axes, cx=1/apex radius x, cy=1/apex radius y, and kx and ky are conic constants relative to the respective x- and y-axes, where −2.0<kx<0.0 and −2.0<ky<0.0;
the peripheral zone being aspheric, rotationally symmetrical about the z-axis, and defined by the equation:
z
=
(
cx
)
(
x
2
)
1
+
1
-
(
1
+
kx
)
(
cx
2
)
(
x
2
)
where z and x are coordinates relative to the respective z- and x-axes, cx=1/apex radius x, and kx is the conic constant, where −2.0<kx<0.0; and
the blending zone forming a smoothened transition between the asphero-toric central zone and the aspheric peripheral zone, the blending zone described at least in part by spline curves, wherein along a cylindrical meridian and a spherical meridian the slope changes of the spline curves in the blending zone are opposite and about the same in magnitude, and along a meridian halfway between the cylindrical and spherical meridians in the blending zone a continuation of the central zone generally matches a continuation of the peripheral zone.
2. The lens of claim 1 , wherein, for the central zone, −1.0<kx<0.0 and −1.0<ky<0.0, and for the peripheral zone, −1.0<kx<0.0, or wherein, for the central zone, −0.7<kx<−0.1 and −0.7<ky<−0.1, and for the peripheral zone, −0.7<kx<−0.1.
3. The lens of claim 1 , wherein, for the central zone, kx=ky=−0.16, and wherein, for the peripheral zone, kx=−0.16.
4. The lens of claim 1 , wherein the blending zone is a circular band having an inner diameter of no less than about 7.0 mm and an outer diameter of between about 7.2 mm and about 9.0 mm.
5. A method of designing the lens of claim 1 , comprising:
defining the asphero-toric central zone of the posterior surface;
defining the aspheric peripheral zone of the posterior lens surface; and
defining the blending zone of the lens surface by generating the spline curves to smoothen the transition between the asphero-toric central zone and the aspheric peripheral zone.
6. An ophthalmic lens, comprising:
a posterior surface having a central optic zone, a peripheral zone, and a blending zone therebetween;
the central zone configured for correcting astigmatism; and
the blending zone forming a smoothened transition between the central zone and the peripheral zone, the blending zone described at least in part by spline curves.
7. The lens of claim 6 , wherein the central zone is asphero-toric and the peripheral zone is spheric, the central zone is sphero-toric and the peripheral zone is aspheric, or the central zone is asphero-toric and the peripheral zone is aspheric.
8. The lens of claim 6 , wherein, along a first cylindrical meridian and a second spherical meridian, the slope changes of the spline curves in the blending zone are opposite, and along a third meridian somewhere between the first and second meridians in the blending zone, a continuation of the central zone generally matches a continuation of the peripheral zone.
9. The lens of claim 8 , wherein the third meridian is halfway between the first and second meridians, and along the first and second meridians, the slope changes of the spline curves in the blending zone have about the same magnitude.
10. The lens of claim 6 , wherein the central zone is circular and the blending zone is a circular band.
11. The lens of claim 10 , wherein the blending zone has an inner diameter of no less than about 7.0 mm and an outer diameter of between about 7.2 mm and about 9.0 mm.
12. The lens of claim 6 , wherein the central zone is oval-shaped and the blending zone is an oval band.
13. The lens of claim 12 , wherein the blending zone has an inner diameter of no less than about 7.0 mm along a cylindrical meridian of the lens and no more than about 12.5 mm along a spherical meridian of the lens.
14. The lens of claim 6 , wherein the blending zone is a varied-width band having a maximum width along a meridian having a greatest slope change between the central and peripheral zones and having a minimum width along a meridian having a smallest slope change between the central and peripheral zones.
15. The lens of claim 14 , wherein the minimum width of the blending zone is about 0.2 mm and the maximum width is about 1.0 mm.
16. A method of designing the lens of claim 6 , comprising:
defining the central zone and the peripheral zone of the posterior lens surface; and
defining the blending zone of the lens surface by generating the spline curves to smoothen the transition between the central zone and the peripheral zone.
17. The method of claim 16 , wherein:
the step of defining the central and peripheral zones comprises defining the central zone as asphero-toric and the peripheral zone as spheric, the central zone as sphero-toric and the peripheral zone as aspheric, or the central zone as asphero-toric and the peripheral zone as aspheric; and
the step of defining the blending zone comprises selecting a conic constant for the central zone, the peripheral zone, or the central and peripheral zones so that, along a first cylindrical meridian and a second spherical meridian, the slope changes of the spline curves in the blending zone are opposite of each other, and along a third meridian somewhere between the first and second meridians in the blending zone, a continuation of the central zone generally matches a continuation of the peripheral zone.
18. An ophthalmic lens, comprising:
a posterior surface having a central optic zone and a peripheral zone, the central zone being asphero-toric and configured for correcting astigmatism, and the peripheral zone being aspheric.
19. The lens of claim 18 , wherein:
the central asphero-toric zone is defined by the equation:
z
=
(
cx
)
(
x
2
)
+
(
cy
)
(
y
2
)
1
+
1
-
(
1
+
kx
)
(
cx
2
)
(
x
2
)
-
(
1
+
ky
)
(
cy
2
)
(
y
2
)
where z, x, and y are coordinates relative to respective z-, x-, and y-axes, cx=1/apex radius x, cy=1/apex radius y, and kx and ky are conic constants relative to the respective x- and y-axes, where −2.0<kx<0.0 and −2.0<ky<0.0; and
the peripheral aspheric zone is rotationally symmetrical about the z-axis and defined by the equation:
z
=
(
cx
)
(
x
2
)
1
+
1
-
(
1
+
kx
)
(
cx
2
)
(
x
2
)
where z and x are coordinates relative to the respective z- and x-axes, cx=1/apex radius x, and kx is the conic constant, where −2.0<kx<0.0.
20. The lens of claim 18 , wherein, for the central zone, −1.0<kx<0.0 and −1.0<ky<0.0, and for the peripheral zone, −1.0<kx<0.0, or wherein, for the central zone, −0.7<kx<−0.1 and −0.7<ky<−0.1, and for the peripheral zone, −0.7<kx<−0.1.
21. The lens of claim 18 , wherein, for the central zone, kx=ky=−0.16, and wherein, for the peripheral zone, kx=−0.16.
22. The lens of claim 18 , further comprising a blending zone between the central and peripheral zones, wherein the blending zone forms a smoothened transition between the central zone and the peripheral zone, and the blending zone is described at least in part by spline curves.
23. The lens of claim 22 , wherein, along a first cylindrical meridian and a second spherical meridian, the slope changes of the spline curves in the blending zone are opposite of each other, and along a third meridian between the first and second meridians in the blending zone, a continuation of the central zone generally matches a continuation of the peripheral zone.
24. The lens of claim 23 , wherein the third meridian is about halfway between the first and second meridians, and along the first and second meridians, the slope changes of the spline curves in the blending zone have about the same magnitude.