Excimer Laser Shot File Calculation Using Dynamic Threshold Dithering
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Solution Overview
Problem
Existing dither algorithms for excimer lasers used in eye treatments and lens production often produce artefacts due to uneven shot densities, particularly in low-density regions where shots are too far apart and in high-density regions where shots are overly frequent, leading to deviations from the desired ablation profile.
Innovation Solution
Adapting the dither algorithm by using a dynamic threshold value based on calculated shot densities, with threshold values ranging from 0% to 100% of the maximum shot density, to optimize the placement of laser shots on a grid, ensuring more accurate ablation profiles by adjusting the grid width and using a cost function to decide shot placement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a constant grid width is used in dither algorithms, then calculation time is reduced and processing is simplified, but artefacts are produced in low-density regions where shots are too far apart and in high-density regions where shots are overly frequent
Solution Approach 1:
The patent applies dynamics by making the grid width variable rather than constant. The grid width dynamically adapts to the local shot density requirements: smaller grid widths in high-density regions to prevent excessive shot frequency, and larger grid widths in low-density regions to maintain adequate shot spacing. This dynamic adjustment resolves the contradiction between calculation efficiency and ablation profile accuracy.
Solution Approach 2:
The patent implements local quality by allowing different grid widths in different regions of the treatment area. Each region's grid width is optimized based on its specific shot density requirements, rather than applying a uniform grid width across the entire area. This local optimization eliminates artefacts in both low-density and high-density regions while maintaining overall calculation efficiency.
2Loss of time
If dither algorithms use only a few neighboring positions for shot placement decisions, then calculation time is saved, but artefacts occur in regions where the distance to neighboring shots is too large
Solution Approach 1:
The patent dynamically adjusts the grid width based on local shot density requirements. In regions where shots are spaced far apart, the algorithm uses a larger grid width to ensure adequate shot placement without requiring consideration of distant neighboring positions. This dynamic approach maintains ablation profile uniformity while limiting the number of neighboring positions that need to be evaluated.
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
The dynamic threshold approach minimizes the difference between the planned and achieved ablation profiles, reducing artefacts and improving the accuracy of laser shot placement, resulting in a more precise and uniform ablation profile that better matches the desired correction, such as for myopia or hyperopia.
Implementation Method 1
an excimer laser system for correction of vision... provides a relatively large spot size which provides a relatively large coverage of treatment area per shot
Implementation Method 2
the excimer laser system provides a relatively large spot size which provides a relatively large coverage of treatment area per shot... to perform various types of corrections, such as myopia, hyperopia, and astigmatism correction
Data Source
AI summary
The invention relates to a method and apparatus for calculating a laser shot file for use in an excimer laser comprising the steps of providing information with respect to a desired ablation profile, calculating the shot density of the desired ablation profile, using a cost function for placing laser shots of the excimer laser on grid positions wherein a threshold value is determined based on the calculated shot density of the desired ablation profile.