Progressive addition power lens

• US 6,776,486 B2
• Filed: 08/09/2002
• Issued: 08/17/2004
• Est. Priority Date: 05/31/2002
• Status: Expired due to Term

• Current Assignee: Crossbows Optical, Ltd. (EssilorLuxottica SA)
• Original Assignee: Crossbows Optical, Ltd. (EssilorLuxottica SA)
• Inventors: Steele, Trevor, McLoughlin, Hugh, Payne, Derek
• Primary Examiner(s): Epps, Georgia
• Assistant Examiner(s): RAIZEN, DEBORAH A
• Application Number:
  US10/214,553
• Publication Number:
  US 20030223033A1
• Time in Patent Office: 739 Days
• Field of Search: 351/169, 351/177, 351/178
• US Class Current: 351/169
• CPC Class Codes: G02C 7/024 Methods of designing ophthalmic lenses
• CPC Class Codes: G02C 7/028 Special mathematical design techniques
• CPC Class Codes: G02C 7/061 Spectacle lenses with progressively varying focal power
• CPC Class Codes: G02C 7/063 Shape of the progressive surface

Abstract

A system and method for designing a progressive lens. Mean power is specified at points distributed over the entire surface of the lens and lens height is specified around the edge of the lens. Lens height is determined at the points consistent with the specified mean power and the lens edge height in part by solving a partial differential equation of the elliptic type subject to the lens edge height as a boundary condition. A successive over-relaxation technique may be employed to converge on the solution to the partial differential equation, and an over-relaxation factor may be determined to most efficiently relax the equation.

Claims

1. A method for designing a progressive lens surface comprising:

specifying mean power at a plurality of points distributed over the entire surface of the lens;

specifying lens height around the edge of the lens; and

determining lens height at the plurality of points consistent with the specified mean power and lens edge height, comprising finding a unique solution of a partial differential equation of the elliptic type subject to a boundary condition of the lens edge height.

2. The method of claim 1, wherein finding the unique solution of the partial differential equation comprises:

employing a successive over-relaxation technique to converge on the solution; and

determining an over-relaxation factor to most efficiently relax the equation.

3. The method of claim 2, wherein the step of determining the lens height at a plurality of points comprises:

defining a mesh comprising a plurality of points over the surface of the lens;

determining mean power at each point on the mesh as defined by the specified mean power distribution over the lens surface; and

numerically solving on the mesh a partial differential equation of the elliptic type, subject to the lens edge height as a boundary condition, to determine the lens height at each point of the mesh.

4. The method of claim 3, wherein the lens comprises a distance area and a reading area, and wherein the step of specifying mean power further comprises:

specifying mean power along a connecting path extending from a first point in the distance area to a second point in the reading area; and

specifying mean power over a coordinate system distributed over the surface of the lens consistently with the mean power specified along the connecting path.

5. The method of claim 4, wherein the coordinate system comprises a set of contour lines, each contour line intersecting the connecting path, and wherein specifying mean power over the coordinate system further comprises specifying mean power variation along the contour lines as a function, the mean power on a contour line and the mean power on the connecting path being equal at every point where a contour line intersects the connecting path.

6. The method of claim 5, further comprising rotating in a controlled manner the specified mean power values with respect to the plurality of points distributed over the lens surface and the specified lens edge height with respect to the edge of the lens.

7. The method of claim 1, wherein the step of determining the lens height at a plurality of points comprises:

defining a mesh comprising a plurality of points over the surface of the lens;

determining mean power at each point on the mesh as defined by the specified mean power distribution over the lens surface; and

numerically solving on the mesh a partial differential equation of the elliptic type, subject to the lens edge height as a boundary condition, to determine the lens height at each point of the mesh.

8. The method of claim 7, wherein the lens comprises a distance area and a reading area, and wherein the step of specifying mean power further comprises:

specifying mean power along a connecting path extending from a first point in the distance area to a second point in the reading area; and

specifying mean power over a coordinate system widely distributed over the entire area of the lens consistently with the mean power specified along the connecting path.

9. The method of claim 8, wherein the coordinate system comprises a set of contour lines, each contour line intersecting the connecting path, and wherein specifying mean power over the coordinate system further comprises specifying mean power variation along the contour lines as a function, the mean power on a contour line and the mean power on the connecting path being equal at every point where a contour line intersects the connecting path.

10. The method of claim 9, further comprising rotating in a controlled manner the specified mean power values with respect to the plurality of points distributed over the lens surface and the specified lens edge height with respect to the edge of the lens.

11. The method of claim 1, wherein the lens comprises a distance area and a reading area, and wherein the step of specifying mean power further comprises:

specifying mean power along a connecting path extending from a first point in the distance area to a second point in the reading area; and

specifying mean power over a coordinate system distributed over the surface of the lens consistently with the mean power specified along the connecting path.

12. The method of claim 11, wherein the step of specifying mean power over the coordinate system further comprises:

specifying mean power in the distance area and reading area; and

specifying mean power over a coordinate system distributed over the remaining area of the lens consistently with the mean power specified along the connecting path.

13. The method of claim 11, wherein the coordinate system comprises a set of contour lines, each contour line intersecting the connecting path, and wherein specifying mean power over the coordinate system further comprises specifying mean power variation along the contour lines as a function, the mean power on a contour line and the mean power on the connecting path being equal at every point where a contour line intersects the connecting path.

14. The method of claim 13, wherein each contour line intersects the connecting path only once and each contour line does not intersect any other contour line.

15. The method of claim 14, wherein the mean power is constant along the length of each contour line.

16. The method of claim 14, wherein the mean power varies along the length of each contour line.

17. The method of claim 11, wherein specifying the lens height around the edge of the lens comprises defining a boundary height profile function in which

the boundary height varies only slightly in a first boundary segment adjacent to the distance area and a second boundary segment adjacent to the reading area, and

the boundary height undergoes substantially smooth transitions between the first and second boundary segments.

18. The method of claim 11, further comprising redistributing astigmatism away from the connecting path.

19. The method of claim 18, wherein the step of redistributing astigmatism comprises:

determining a change in mean power required to reduce astigmatism on the connecting path;

distributing the change in mean power across the lens to modify the specified mean power values;

determining lens height at the points of the plurality of points distributed over the lens surface using the modified mean power values at the points.

20. The method of claim 1, further comprising rotating in a controlled manner the specified mean power values with respect to the plurality of points distributed over the lens surface and the specified lens edge height with respect to the edge of the lens.

21. The method of claim 20, wherein the rotation is controlled by an angle-dependent handing function H(θ

) such that M(ρ

,θ

)→

M(ρ

,H(θ

)) and z(θ

)→

z(H(θ

)) where M is mean power, z(θ

) is the lens edge height, and (ρ

,θ

) are polar coordinates over the area of the lens.

29. A system for designing a progressive lens comprising a processor for calculating lens height at a plurality of points over the lens surface according to the method of claim 1.

22. A progressive lens comprising a surface having a variable height and including a distance area and a reading area, wherein mean power over the lens surface varies according to a set of curves forming iso-mean power contours on the lens surface and a contour defining an area of constant mean power in the distance area that is substantially elliptical, and wherein mean power M varies along a connecting path extending from a first point in the distance area to a second point in the reading area according to a function of the form:

$M<br><br>\left(y\right)=M_D+\left[\frac{M_R-M_D}{2}\right]\left[1-\cos <br><br>\left(\mathrm{\pi <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>\frac{y_D-y}{y_D-y_R}\right)\right]$

where M_D is mean power specified at the a first point (0,y_D) in the distance area and M_R is mean power specified at the second point (0,y_R) in the reading area.

23. The progressive lens of claim 22, where astigmatism along the connecting path is less than 0.15*(M_R−

M_D) where M_D is mean power specified at the first point in the distance area and M_R is mean power specified at the second point in the reading area.

24. A system for manufacturing a progressive lens, the system comprising:

a processor for accepting inputs defining mean power variation over a coordinate system covering the surface of the lens and defining lens height around the edge of the lens and for calculating lens height at a plurality of points over the lens surface by solving an elliptic partial differential equation subject to the lens height at the edge of the lens as a boundary condition; and

a memory for storing the calculated lens height values.

25. The system of claim 24, further comprising a numerically controlled milling machine for accepting the calculated lens height values and using the calculated lens height values for machining the lens or a mold for producing the lens or a former for producing the lens.

26. The system of claim 25, wherein the numerically controlled milling machine adjusts the calculated lens height values in accordance with the type of machining tool fitted to the milling machine.

27. A system for manufacturing a progressive lens, the system comprising:

means for accepting inputs defining mean power variation over a coordinate system covering the surface of the lens and defining lens height around the edge of the lens and for calculating lens height at a plurality of points over the lens surface by solving an elliptic partial differential equation subject to the lens height at the edge of the lens as a boundary condition; and

means for storing the calculated lens height values.

28. The system of claim 27, further comprising means for accepting the calculated lens height values and using the calculated lens height values for machining the lens or a mold for producing the lens or a former for producing the lens.

30. A system for designing progressive lens, the system comprising:

a processor for accepting inputs defining mean power variation over a coordinate system covering the surface of the lens and defining lens height around the edge of the lens and for calculating lens height at a plurality of points over the lens surface by solving an elliptic partial differential equation subject to the lens height at the edge of the lens as a boundary condition; and

a memory for storing the calculated lens height values.

31. A system for designing a progressive lens comprising:

means for accepting inputs defining mean power variation over a coordinate system covering the surface of the lens and defining lens height around the edge of the lens and for calculating lens height at a plurality of points over the lens surface by solving an elliptic partial differential equation subject to the lens height at the edge of the lens as a boundary condition; and

means for storing the calculated lens height values.

32. A progressive lens comprising a surface having a variable height and including a distance area and a reading area, wherein mean power over the lens surface varies according to a set of curves forming iso-mean power contours on the lens surface and a contour defining an area of constant mean power in the distance area that is substantially elliptical, and where astigmatism along the connecting path is less than 0.15* (M_R−

M_D) where M_D is mean power specified at a first point (0,y_D) in the distance area and M_R is mean power specified at a second point (0,y_R) in the reading area.