Regressive Progressive Lens Design for Gradient Control

The patent applies parameter changes by modifying the surface design parameters of the progressive lens. Specifically, it introduces a regressive surface with controlled sphere and cylinder gradients, where the fourth derivative of the sphere value with respect to altitude is limited to less than 5.0 × 10^-5 mm^-2 diopter^-1. This parameter control reduces the steepness of optical power variations across the lens surface, making the lens less sensitive to positioning errors during manufacturing while maintaining the required optical correction functionality.

The patent changes the parameter distribution across the lens surface by implementing a regressive design where sphere and cylinder gradients are controlled. The key parameter constraint is that the fourth derivative of the sphere value with respect to altitude must be less than 5.0 × 10^-5 mm^-2 diopter^-1. This creates a smoother transition of optical power across the lens, reducing the impact of positioning errors while preserving the necessary optical correction for presbyopic wearers.

While the surface design does introduce additional parameter constraints (controlling fourth derivatives), the patent simplifies the overall manufacturing approach by working with a regressive surface geometry that has more gradual transitions. This allows for more forgiving machining tolerances and less sensitive positioning requirements during digital surfacing, potentially offsetting the increased complexity of the surface design itself through improved manufacturing robustness.