Progressive Addition Lenses Reducing Base Out Prism
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Solution Overview
Problem
Progressive addition lenses (PALs) induce unwanted base out prism when transitioning from distance to near vision, increasing convergence demand and causing eye strain due to the inherent design of prism changes across the lens surfaces.
Innovation Solution
The lens design modifies the major surfaces using Cartesian coordinate points and weighting factors to minimize disruption to optical properties, specifically reducing base out prism by altering the tilt and prism properties across zones from the distance to near portion, utilizing functions Fx and Fy to control prism changes and maintain minimal distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the lens design provides add power for near vision by traditional PAL configuration, then near vision capability is improved, but base out prism increases causing eye strain
Solution Approach 1:
The patent applies different surface modifications to different zones of the lens. The distance portion maintains traditional optical properties, while the near portion applies specific surface modifications (aspherical design, prism reduction) to locally address the base out prism issue without affecting distance vision quality.
Solution Approach 2:
The patent modifies optical parameters in the near portion of the lens, specifically changing the surface curvature, aspherical coefficients, and prism characteristics to reduce base out prism while maintaining the necessary add power for near vision. This involves adjusting dioptric power distribution and surface geometry parameters.
2Adaptability or versatility
If the lens surface is altered to create add power, then near vision is enabled, but optical properties of the lens are disrupted
Solution Approach 1:
The lens is divided into distinct functional zones: a distance portion with traditional optical properties and a near portion with modified surface characteristics. This segmentation allows independent optimization of each zone's optical properties without compromising the other.
Solution Approach 2:
Surface modifications including aspherical design and prism reduction are applied locally to the near portion while keeping the distance portion unchanged, thereby enabling add power without disrupting the overall optical quality of the lens.
3Ease of operation
If prism changes are made across the lens surfaces, then convergence demand is affected, but eye strain increases
Solution Approach 1:
The lens design preemptively compensates for excessive convergence demand by incorporating prism reduction in the near portion. This preliminary anti-action counteracts the base out prism that would otherwise be induced by the add power, preventing eye strain before it occurs.
Solution Approach 2:
The patent adjusts prism parameters and surface tilt angles in the near portion to optimize convergence demand. By modifying these optical parameters, the lens reduces the excessive convergence required for near vision while minimizing eye strain.
Data Source
AI summary
The invention generally relates to a lens and the method of manufacturing progressive addition lenses (PAL) to remove unwanted base out prism and minimize excessive convergence, comprising determining basic configuration of two major lens surfaces to provide a distance portion and near portion, wherein diopter power increases from the distance portion of the lens to the near portion; selecting an amount of prism reduction; and reducing base out prism that inherently occurs as diopter power increases by altering the configuration of the lens as a function of the amount of prism reduction to minimize any disruption of optical properties a lens while decreasing base out prism.