Multifocal optical device design

Abstract

Multifocal optical device designs receive input parameters to specify a desired power distribution function, a power deviation weight function, and an astigmatism weight function over the design field. A fourth-order partial differential variational equation is linearized by defining the optical surface in terms of perturbations from a base surface such as a sphere or a toric. The solution may be expressed as piecewise quadratic splines superposed over a triangulation of the field. Evaluation of the surface may use a set of tensor-product splines. An astigmatic base surface permits both multiple magnifying powers and a prescribed astigmatism correction in a single optical surface.

Description

TECHNICAL FIELD The present invention relates to computer-implemented methods and systems for designing optical devices, and particularly concerns the design of multifocal devices such as progressive ophthalmic lenses. BACKGROUND Multifocal optical devices find utility in a number of technologies. For example, bifocal and trifocal lenses treat presbyopia caused by loss of accommodative power of the eye. Progressive addition lenses for this purpose include a far-view zone with a low power for distance vision and a near-view zone with higher power for reading and other close work. The power increases progressively and smoothly in an intermediate zone or corridor between the far and near zones. Normally, the near zone lies near the bottom center of the lens, below the far zone; however, other arrangements satisfy specialized purposes. Lens design generates a specification of surface points that a grinder can produce from a lens blank. Modern lens grinders are numerically controlled ...

AI Technical Summary

Benefits of technology

The patent describes a way to design optical devices that can correct astigmatism and have precise power distribution. This is done by using a prescribed power distribution, a weight function for power deviation, and one for astigmatism. The solution is obtained by solving a linearized variational equation as perturbations over a base surface, and can be expressed in terms of superposed low-degree splines. Additionally, the patent also mentions that the device can have both progressive-power and astigmatism corrections in the same optical surface by incorporating a prescribed cylinder into the base surface.

Problems solved by technology

Astigmatism is normally an undesirable property of lenses that causes distortion and color fringing.

Direct methods usually result in a high astigmatism level with little control over the astigmatism in different areas of the lens surface.

Indirect methods balance a desired power distribution with the unavoidable astigmatism produced.

Indirect methods involve the solution of fourth-order nonlinear elliptic equations, which involve very large amounts of computation—up to several hours for a single lens design.

However, progressive design techniques have heretofore not integrated astigmatism correction, and fabricating the two corrections sequentially on the same surface would unacceptably thin the lens or device.

Although this makes the two corrections approximately independent of each other, some offset errors still exist, and structural weakness may still occur, especially in currently fashionable thin, light ophthalmic lenses.

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