Bifocal Spectacle Lens Independent Portion Optimization
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Solution Overview
Problem
Existing methods for producing bifocal spectacle lenses fail to adequately account for the tilt of the lens in front of the eye, leading to unsatisfactory optical quality and aesthetically unpleasing visible near portions and edges.
Innovation Solution
A computer-implemented method for creating a numerical representation of a bifocal spectacle lens using free-form technology, where the lens is optimized for distance and near vision portions independently, with a transition section ensuring a continuous and smooth transition between the two portions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the near portion is elevated and cast from the same material as the distance portion, then the manufacturing process is simplified, but the optical quality becomes unsatisfying due to inability to account for lens tilt and centre of rotation requirements
Solution Approach 1:
The lens is divided into a distance portion and a near portion that are optimized independently. The distance portion is optimized for distance vision with appropriate tilt and centration, while the near portion is optimized for near vision with its own geometric parameters. This segmentation allows each portion to meet its specific optical requirements without compromising the other.
Solution Approach 2:
Each portion of the lens (distance and near) is given its own local optimization parameters including tilt, centration, and surface geometry tailored to its specific viewing distance requirements. The distance portion has parameters optimized for infinity viewing while the near portion has parameters optimized for close work, allowing each region to have the quality needed for its function.
2Ease of operation
If the near portion is made visible and raised in the case of polymers, then the near vision function is achieved, but the aesthetics become unpleasing
Solution Approach 1:
The transition between the distance and near portions is achieved by introducing a third dimension - a progressive transition zone that smoothly varies the optical power and surface geometry. This gradual transition in the vertical and horizontal dimensions allows the near portion to be functional while minimizing its visual prominence and creating a more aesthetically pleasing appearance.
3Manufacturing precision
If the upper separating line of the near portion is fitted to the level of the lower edge of the iris, then the near vision coverage is optimized, but the tilt of the spectacle lens cannot be taken into account in production
Solution Approach 1:
The lens is designed with preliminary built-in tilt and centration parameters that are incorporated during the manufacturing optimization process. The distance portion and near portion are each optimized with predetermined tilt angles and centration values that account for typical spectacle fitting conditions, allowing the lens to be produced with these parameters already integrated rather than requiring adjustment during fitting.
4Manufacturing precision
If independent optimization of distance and near portions is performed, then the optical power fitting is precise, but the transition between portions must be carefully managed to ensure continuity
Solution Approach 1:
A transition zone is introduced as an intermediary region between the distance and near portions. This transition zone serves as a mediator that smoothly connects the two independently optimized portions, gradually varying the optical power and surface geometry from the distance portion parameters to the near portion parameters, ensuring optical continuity and eliminating abrupt transitions.
Data Source
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AI summary
A bifocal spectacle lens (1) and a method for creating a numerical representation of a bifocal spectacle lens (1) are made available. The bifocal spectacle lens (1) comprises a distance portion (3), a near portion (5) and a transition section (7) situated between the distance portion (3) and the near portion (5). The distance portion (3) is optimized in view of optical power for distance vision and the near portion (5) is optimized in view of optical power for near vision. The transition section (7) is determined in such a way that the latter creates a continuous transition between the distance portion (3) and the near portion (5). The distance portion (3) and the near portion (5) are optimized independently of one another and put together with the transition section (7) to form the numerical representation of the bifocal spectacle lens (1). The transition section is determined by providing an overlap region between the distance portion and the near portion where a surface of the overlap region is a linear combination of a surface of the distance portion and a surface of the near portion in the overlap region.