Contact Lens Junction Thickness Control for Toric Stability
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Solution Overview
Problem
Existing contact lenses struggle to achieve consistent wear comfort and circumferential stability due to disparities in junction thickness caused by varying cylindrical axial angles, leading to issues like irregular torque and poor stability, especially in toric lenses with different cylindrical power settings.
Innovation Solution
A method of manufacturing contact lenses that involves establishing junction thickness at multiple sites around the geometrical center axis, determining the joint zone position to match these thickness values, and maintaining constant or varying thickness along the circumference to balance wear comfort and stability, regardless of optical zone profiles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the optical zone profile is adjusted to provide appropriate cylindrical power and axial angle for astigmatism correction, then the optical characteristics are improved, but disparities in junction thickness in the joint zone arise, leading to poor wear comfort and circumferential stability
Solution Approach 1:
The patent applies local quality by establishing specific junction thickness values at different circumferential locations in the joint zone. Instead of requiring uniform thickness throughout, the invention specifies that the junction thickness should be established at multiple sites (e.g., 0°, 45°, 90°, 135°, 180°, 225°, 270°, 315°) with appropriate thickness values that may vary by location, allowing the optical zone to have the necessary cylindrical power and axial angle while maintaining controlled thickness characteristics for wear comfort and stability.
2Reliability
If the cylindrical axial angle is set to 180° to correct astigmatism, then the optical correction is achieved, but the joint zone becomes thicker at vertical edges, resulting in poor wear comfort and circumferential stability
Solution Approach 1:
The patent addresses this by establishing junction thickness at multiple circumferential sites around the joint zone. For a 180° cylindrical axial angle lens, the invention specifies appropriate thickness values at different angular positions (e.g., thinner at vertical edges, thicker at horizontal edges or intermediate positions) to balance the optical correction requirement with wear comfort, preventing excessive thickness at any single location while maintaining the necessary astigmatism correction.
3Reliability
If the cylindrical axial angle is set to 45° for astigmatism correction, then the optical characteristics are improved, but irregular torque arises due to asymmetrical profile, leading to poor circumferential stability
Solution Approach 1:
The patent resolves this contradiction by establishing junction thickness at multiple circumferential sites including symmetric positions (0°, 45°, 90°, 135°, 180°, 225°, 270°, 315°). For a 45° cylindrical axial angle, the invention specifies thickness values that create a balanced distribution pattern, where the joint zone thickness varies in a controlled manner around the circumference rather than being asymmetric. This balanced thickness distribution reduces irregular torque while maintaining the necessary optical correction characteristics.
4Ease of operation
If the optical zone diameter is reduced to minimize thickness disparities in the joint zone, then wear comfort is improved, but the optical zone may become too small to provide adequate optical correction
Solution Approach 1:
The patent resolves this by establishing junction thickness at multiple circumferential sites around the joint zone rather than uniformly reducing the optical zone diameter. This allows the optical zone to maintain its necessary size for adequate optical correction while the joint zone thickness is controlled at specific locations to ensure wear comfort. The invention decouples the optical zone dimensions from the joint zone thickness control, allowing independent optimization of both functions.
Data Source
Figure 1(a)~1(c)
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AI summary
A novel method for manufacturing a contact lens in which wearing comfort and stability in the circumferential direction that are aimed at can be achieved consistently with a high degree of accuracy irrespective of a profile of an optical zone. An optical zone (22) provided in a center of a lens has a concave rear surface optical zone (20) substantially matching a surface profile of a cornea and has a convex front surface optical zone (18) imparting required spherical diopter power and geometrical center thickness, and a face of either the rear surface optical zone (20) or the front surface optical zone (18) is designed to impart thereto cylindrical power and axial angle required for a toric surface. Furthermore, a junction thickness is established in a joint zone (34) that connects the optical zone (22) with a peripheral zone (24) at multiple sites in a circumferential direction about a geometrical lens center axis (12) of the optical zone (22). Position of the joint zone (34) is determined on the circumference from profiles established on the rear surface optical zone (20) and the front surface optical zone (18) so as to connect points satisfying the junction thickness thusly established.