Progressive Power Lens Toric Surface Design for Image Sway Reduction
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Solution Overview
Problem
There is a need for a progressive power lens that minimizes image sway and magnification differences between distance and near portions, providing a comfortable field of view and effective vision correction.
Innovation Solution
The method involves designing a progressive power lens with toric surfaces on both the object-side and eyeball-side surfaces, where the surface power in the horizontal direction is greater than in the vertical direction, and the structure is tailored based on whether the prescription is for a far-sight or near-sight system, using specific conditions to adjust the surface powers to reduce image sway and enhance vision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a spherical surface with constant base curve is used on the object-side surface, then magnification variations due to shape factor are suppressed, but the lens cannot correct astigmatism effectively
Solution Approach 1:
The patent introduces a toric surface on the object-side surface, which has asymmetric curvature in different directions (horizontal and vertical meridians). This asymmetric surface allows the lens to correct astigmatism while maintaining controlled magnification characteristics through specific design of the toric parameters
Solution Approach 2:
The patent applies different surface powers in different directions at different locations on the lens. The toric surface elements have different surface powers in horizontal and vertical directions, and these are optimized locally at distance and near portions to achieve both astigmatism correction and magnification control
2Reliability
If toric surface elements are added to correct astigmatism, then astigmatism correction is improved, but image sway and magnification differences increase
Solution Approach 1:
The patent optimizes specific parameters of the toric surface, including the surface power differences between horizontal and vertical directions, and between distance and near portions. By carefully controlling these parameters, the lens achieves astigmatism correction while minimizing image sway and magnification differences
Solution Approach 2:
The patent creates a progressive power lens where the toric surface elements are distributed dynamically across the lens surface, with different surface power characteristics at different vertical positions (distance vs near portions). This dynamic distribution allows the lens to adapt to different viewing distances while maintaining stable image characteristics
3Stability of the object's composition
If the average surface power difference between distance and near portions is reduced, then magnification difference is minimized, but the addition power cannot be achieved
Solution Approach 1:
The patent divides the lens into distinct functional zones (distance portion and near portion) with different surface power characteristics. The toric surface elements are segmented and optimized for each zone, allowing the distance portion to have lower surface power difference for magnification consistency, while the near portion provides the necessary addition power for near vision
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach results in a progressive power lens with reduced image sway and improved vision, providing a comfortable field of view and effective vision correction by minimizing magnification differences and aberrations.
Implementation Method 1
the object-side surface includes at least one of elements of a toric surface with the surface power OHPf greater than the surface power OVPf and elements of a toric surface with the surface power OHPn greater than the surface power OVPn, and the eyeball-side surface along the principal meridian or the vertical reference line includes elements that cancel shifts in the surface power by the elements of the toric surface on the object-side surface
Data Source
Figure 1~2B
Figure 3A~3C
Figure 4~5
AI summary
A progressive power lens with less image sway is provided. A method of designing a progressive power lens includes preferentially selecting a spectacle specification including a first condition if an average prescription power of a distance portion is equal to or greater than +3.0 D, and preferentially selecting a spectacle specification including a second condition if the average prescription power is equal to or smaller than -3.0 D. In a progressive power lens, at least a surface power OHPf in a horizontal direction of a distance portion on an object-side surface is greater than a surface power OVPf in a vertical direction, or a surface power OHPn in a horizontal direction of a near portion is greater than a surface power OVPn in a vertical direction. An eyeball-side surface includes elements that cancel shifts in the surface power by elements of a toric surface on the object-side surface. The first condition includes a condition that the surface power OVPf is greater than the surface power OVPn, and the second condition includes a condition that the surface power OVPf is smaller than the surface power OVPn.