Progressive Addition Lens Power Deviation Correction
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Solution Overview
Problem
Conventional progressive addition lenses face issues with astigmatism and power error in the peripheral part of the distance area, where astigmatism reduction leads to increased power error, and existing methods fail to improve both astigmatism and power error simultaneously.
Innovation Solution
A progressive addition lens design where the prescription value T, calculated from the formula 'S + C/2', results in a power deviation ΔD that is either negative or positive, allowing the spherical equivalent power to shift appropriately in the distance area, reducing power error and astigmatism by positioning the point yc within specific ranges relative to the distance vision measurement point and progressive starting point.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If aspherical loading is set to reduce astigmatism in the peripheral part of the distance area, then astigmatism is reduced, but power error from the prescribed spherical equivalent power becomes maximum in the peripheral part
Solution Approach 1:
The patent applies parameter changes by modifying the spherical equivalent power distribution across the lens. Specifically, it sets the spherical equivalent power to be smaller than the prescribed value in the peripheral part of the distance area (creating a negative power deviation), which compensates for the power error generated by aspherical loading and maintains optimal optical performance in peripheral regions.
2Manufacturing precision
If the spherical equivalent power is set to match the prescribed value at the progressive starting point, then power accuracy is maintained at this point, but power error becomes maximum in the peripheral part of the distance area
Solution Approach 1:
The patent applies local quality by creating different power deviation characteristics in different regions of the lens. The spherical equivalent power is set to match the prescribed value at the progressive starting point (zero power deviation), while intentionally setting it to be smaller than the prescribed value in the peripheral part (negative power deviation). This regional differentiation optimizes both central and peripheral optical performance.
3Ease of manufacture
If conventional power setting methods are used, then manufacturing is simplified, but both astigmatism and power error in the peripheral part of the distance area cannot be improved simultaneously
Solution Approach 1:
The patent modifies the spherical equivalent power parameter across different lens regions to simultaneously reduce both astigmatism and power error. By setting the spherical equivalent power to be smaller than the prescribed value in the peripheral part of the distance area, the invention creates a negative power deviation that compensates for errors while maintaining compatibility with conventional manufacturing methods.
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 design effectively reduces astigmatism and power error in the peripheral part of the distance area, maintaining optical performance and allowing for conventional manufacturing methods, while improving visual acuity and reducing blur indices.
Implementation Method 1
at least one of an eyeball side surface of a wearer and an object side surface in the progressive addition lens is formed into an aspheric form
Data Source
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AI summary
There is provided a progressive addition lens capable of improving both of astigmatism and power error on a peripheral part of a distance area, including a distance area used for a distance vision, and other area different from the distance area, wherein at least one of an eyeball side surface of a wearer and an object side surface in the progressive addition lens is formed into an aspheric form, and when a prescription value T to be obtained from formula "S+C/2" expressed by a prescribed spherical power S and a cylindrical power C, is minus, the area where a power deviation ΔD of a spherical equivalent power D from the prescription value T goes negative, exists on principal sight line in the distance area.