Multifocal Toric Contact Lens Axis Stabilization Design
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Solution Overview
Problem
Multifocal toric contact lenses face challenges in mass production due to distorted shapes, foreign body feeling, and axis stability issues, particularly when combining toric and multifocal features, leading to suboptimal correction of astigmatism and presbyopia with compromised wearing comfort.
Innovation Solution
A contact lens design featuring a convex front surface with a concave rear surface, divided into optical and peripheral portions with specific smoothing and auxiliary portions to maximize horizontal thickness and minimize vertical thickness, ensuring mirror image symmetry and continuous surface transitions for improved centering and axis stability, using hydrogel or silicone hydrogel materials for enhanced comfort.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a multifocal toric contact lens with truncation is used, then axis stability is improved, but the lens shape becomes distorted causing foreign body feeling and mass production becomes difficult
Solution Approach 1:
The contact lens is divided into multiple functional zones: a central optical zone for vision correction, a transition zone for gradual power change, and a peripheral zone for axis stabilization. This segmentation allows each zone to perform its specific function without compromising the overall lens shape or causing foreign body sensation.
Solution Approach 2:
Different regions of the contact lens are assigned different optical powers and structural characteristics. The central zone has specific power for astigmatism and presbyopia correction, while the peripheral zone has modified power and thickness to provide axis stability. This local differentiation enables mass production of lenses with stable axis without requiring custom shaping for each patient.
2Stability of the object's composition
If a ridge is added to the lower part of the lens for engagement with the lower eyelid, then positional stability is improved, but the upper eyelid easily hits the ridge causing inferior wearing feeling
Solution Approach 1:
The axis stabilization function is extracted from the central optical zone and relocated to the peripheral zone of the contact lens. By removing the ridge structure from the lower part and instead creating a peripheral zone with modified power and thickness, the lens achieves positional stability without creating protruding structures that would contact and irritate the eyelids.
Solution Approach 2:
Instead of adding vertical relief features (ridges) that extend into the optical path and may contact eyelids, the invention uses horizontal differentiation in the peripheral zone. The axis stabilization is achieved through a broader, flatter peripheral region with modified optical properties, shifting the stabilization mechanism from a vertical dimension approach to a horizontal dimension approach that does not interfere with eyelid movement.
3Stability of the object's composition
If prism ballast is formed over the entire lens, then axis stability is improved, but the prism acts as a hindrance factor for correcting distance and near vision
Solution Approach 1:
The contact lens is divided into distinct functional zones with different optical powers. The central optical zone maintains the precise power distribution needed for astigmatism and presbyopia correction, while the peripheral zone contains the modified power structure for axis stabilization. This segmentation prevents the prism ballast from interfering with the optical correction in the central viewing area.
Solution Approach 2:
Different optical powers are assigned to different regions of the lens. The central zone has optimized power for clear vision at various distances, while the peripheral zone has modified power characteristics specifically for providing rotational stability. This local differentiation ensures that the axis stabilization mechanism does not act as a hindrance to optical correction where it is most needed.
4Ease of operation
If the lens is processed to obtain balance by scraping, then centering is improved, but the entire lens becomes distorted causing foreign body feeling
Solution Approach 1:
The axis stabilization features are built into the lens design during the manufacturing process itself, rather than requiring post-manufacturing adjustments or scraping. The peripheral zone with modified power and thickness is created directly in the molding process, ensuring the lens has inherent centering capability and rotational stability without needing subsequent mechanical modifications that would distort the lens shape.
Data Source
Figure 1A
Figure 1B
Figure 2A
AI summary
There is provided a contact lens having a convex front surface and a concave rear surface, the front surface being divided into an optical portion, an edge joining the front and rear surfaces, a first smoothing portion arranged on an outer periphery of the optical portion, a peripheral portion arranged on an outer periphery of the first smoothing portion, and a second smoothing portion connecting the peripheral portion and the edge, the front surface having mirror image symmetry with respect to a vertical meridian as a boundary extending from an upper end of the lens to a lower end of the lens passing through a midpoint of the lens, and having mirror image symmetry also with respect to the horizontal meridian perpendicular to the vertical meridian at the lens midpoint, the peripheral portion being arranged to include the horizontal meridian, and configured of: a first peripheral portion arranged to include the horizontal meridian and having a shape so as to maximize a thickness of the contact lens on the horizontal meridian, a second peripheral portion arranged to include the vertical meridian and having a shape so as to minimize the thickness of the contact lens on the vertical meridian, a first peripheral auxiliary portion which is a portion adjacent to the first peripheral portion, having a surface shape so as to keep the thickness of the contact lens constant; and an inclined portion which is a portion connecting the first peripheral auxiliary portion and the second peripheral portion to form a continuous surface, and having a surface shape that changes the thickness of the contact lens.