Toric Contact Lens Blending Zone Design
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional toric contact lenses cause irritation due to a pronounced ridge at the junction of the central and peripheral zones, leading to corneal epithelial staining, especially when made from stiff materials like silicon-hydrogel, as the steep-to-flat slope change applies pressure on the cornea.
Innovation Solution
The design incorporates a blending zone that smoothly transitions between the asphero-toric central and aspheric peripheral zones, minimizing slope changes and pressure on the eye, using a posterior surface with a circular or oval blending zone of varying width to match the curvature continuations along specific meridians, reducing the ridge formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a conventional toric lens with sphero-toric central zone and spherical peripheral zone is used, then manufacturing is easier and less expensive, but a pronounced ridge forms at the junction causing corneal pressure and irritation
Solution Approach 1:
The patent applies aspheric surfaces to both the central and peripheral zones, replacing the conventional spherical surfaces. The aspheric central zone has a flatter slope away from the optic axis, and the aspheric peripheral zone also has a flatter slope away from the optic axis. This curvature modification eliminates the abrupt slope change at the junction that creates the harmful ridge, while still allowing for practical manufacturing through molding techniques.
2Measurement precision
If the central zone has a steep slope to correct astigmatism, then visual acuity is improved, but the transition to the peripheral zone creates a pronounced ridge that causes discomfort
Solution Approach 1:
The patent applies different surface characteristics to different regions of the lens. The central zone maintains the necessary steep slope for astigmatism correction with its asphero-toric surface, while the peripheral zone has a flatter aspheric surface. The blending zone smoothly transitions between these two regions, providing locally optimized properties: steep where needed for vision correction, flat where needed for comfort, with a smooth transition eliminating the harmful ridge.
3Ease of operation
If a blending zone is added to smooth the transition between zones, then comfort is improved, but the lens design becomes more complex
Solution Approach 1:
The patent introduces a blending zone as an intermediary region between the central and peripheral zones. This blending zone has an aspheric surface that smoothly transitions the curvature from the steeper central zone to the flatter peripheral zone. While this adds a design element, it eliminates the harmful ridge and significantly improves comfort, with the complexity being manageable through modern lens design and manufacturing processes.
Data Source
Figure 1~2
Figure 3~4
Figure 4A
AI summary
Ophthalmic lenses for correcting astigmatism having a posterior surface with a central optic zone, a peripheral zone, and a blending zone therebetween. The surface of the central zone may be asphero-toric and the surface of the peripheral zone aspheric, with these flatter slopes smoothening out the transition between the central and peripheral zones. The blending zone gradually transitions the curvatures of the central and peripheral zones to further smoothen out the central-to-peripheral-zone transition.