Method and apparatus for calculating a laser shot file for use in an excimer laser

1. An apparatus for calculating a laser shot file for use in an excimer laser for performing a refractive laser treatment of an eye or for producing a customized contact lens or an intraocular lens, the apparatus comprising:

a computer system configured to receive information with respect to a desired ablation profile and implement a dither algorithm,

wherein the dither algorithm is adapted to the desired ablation profile by using a dynamic threshold depending on the shot density of the desired ablation profile for calculating the laser shot file.

2. The apparatus of claim 1 , wherein the computer system is configured to discretize the desired ablation profile on a given grid when implementing the dither algorithm and decide for each grid position whether to place a laser shot of the excimer laser on said grid position.

3. The apparatus of claim 2 , wherein the dither algorithm is using a cost function for determining for each grid position whether to place a laser shot of the excimer laser on said grid position.

4. The apparatus of claim 2 , wherein the computer system is configured to decide whether to place a shot on a given grid position using information regarding a corresponding decision with regard to grid positions in the neighborhood of the given grid position.

5. The apparatus of claim 2 , wherein the computer system is configured to sort the placed laser shots.

6. The apparatus of claim 1 wherein the computer system is configured to calculate a shot density for obtaining the desired ablation profile,

wherein said dynamic threshold is defined depending on the calculated shot density of the desired ablation profile.

7. The apparatus of claim 1 , wherein the computer system is configured to select at least two different threshold values depending on the desired ablation profile.

8. The apparatus of claim 7 , wherein a first threshold value is selected for a desired ablation profile having low shot densities and/or a second threshold value is selected for a desired ablation profile having high shot densities, wherein said first threshold value is lower than said second threshold value.

9. The apparatus of claim 7 , wherein the first threshold value is a value within a range of 0% to 20% of a maximum shot density of the desired ablation profile and/or the second threshold value is a value within a range of 20% to 80% of the maximum shot density and/or a third threshold value is a value within a range of 80% to 100% of the maximum shot density.

10. The apparatus of claim 1 , wherein the computer system is configured to determine the threshold value TV(x, y) in relation to the shot density of the desired ablation profile D(x, y) according to the equation:

TV( x,y )= f ( D ( x,y )).

11. The apparatus of claim 1 , further comprising:

means for determining the threshold value TV(x, y) as a linear relationship to the shot density of the desired ablation profile D(x, y) according to the following equation:

TV( x,y )= a·D ( x,y ),

wherein a is a factor greater than zero and less than or equal to 1.5.

12. The apparatus of claim 11 , further comprising:

means for setting the threshold value to a value equal or nearby the value of the shot density.

13. The apparatus of claim 1 , wherein the computer system is configured to determine a grid width of the given grid based on the calculated shot density of the desired ablation profile.

14. The apparatus of claim 1 wherein the computer system is configured to divide a desired ablation profile into at least two ablation sub-profiles, calculate the shot density of each of said ablation sub-profiles, and determine a respective grid width based on the respective calculated shot density of each of the ablation sub-profiles.

15. The apparatus of claim 1 , wherein the excimer laser provides a laser beam at a spot size fixed between 0.5 mm and 3.5 mm in diameter.