METHOD AND APPARATUS FOR CALCULATING A LASER SHOT FILE FOR USE IN A REFRACTIVE EXCIMER LASER
The invention relates to a method and apparatus for calculating a laser shot file for use in a refractive excimer laser comprising the steps of providing information with respect to a desired ablation profile, calculating the shot density of the desired ablation profile, determining a grid width of a grid being used for placing laser shots of the excimer laser on grid positions wherein the grid width is determined based on the calculated shot density of the desired ablation profile.
1 . A method for calculating a laser shot file for use in an excimer laser preferably for performing a refractive laser treatment of an eye or for producing a customized contact lens or an intraocular lens comprising the steps of providing information with respect to a desired ablation profile, calculating a shot density for obtaining the desired ablation profile, determining a grid width of a grid being used for placing laser shots of the excimer laser on grid positions wherein the grid width is determined based on the calculated shot density of the desired ablation profile.
2 . The method of claim 1 , wherein the grid width is determined such that within a treatment zone a minimum number of grid positions receive one laser shot in sub-areas where the calculated shot density is low and/or such that a maximum number of grid positions receive one laser shot in sub-areas where the calculated shot density is high.
3 . The method of claim 2 , wherein within the treatment zone the minimum number of grid positions in sub-areas where the calculated shot density is low is at least 4 percent, preferably at least 10 percent and more preferably at least 20 percent of grid positions in said sub-areas where the calculated shot density is low.
4 . The method of claim 2 or 3 , wherein within the treatment zone the maximum number of grid positions in sub-areas where the calculated shot density is high is not more than 96 percent, preferably not more than 90 percent and more preferably not more than 80 percent of grid positions in said sub-areas where the calculated shot density is high.
5 . The method of any of the foregoing claims, wherein the grid width C is determined by using the equation:
G =√{square root over ( V Shot *D max ( x, y )/ z max ( x, y ))}{square root over ( V Shot *D max ( x, y )/ z max ( x, y ))},
wherein
V Shot is the ablation volume of a single laser shot,
D max (x, y) is the local maximum shot density at a grid position P(x,y),
z max (x, y) is the maximum value of the ablation profile at the grid position P(x,y).
6 . The method of any of the foregoing claims further comprising the step of calculating the placement of the laser shots of the excimer laser on grid positions using a dither algorithm.
7 . The method of claim 6 further comprising the step of deciding for each grid position whether to place a laser shot or not by using a cost function of the dither algorithm.
8 . The method of claim 7 wherein in the step of deciding whether to place a shot on a given grid position a corresponding decision with regard to the grid positions in the neighborhood of the given grid position is taken into account.
9 . The method of any of the foregoing claims further comprising the step of dividing a desired ablation profile into at least two ablation sub-profiles, calculating the shot density of each of said ablation sub-profiles, determining a respective grid width based on the respective calculated shot density of each of the ablation sub-profiles.
10 . The method of any of claims 6 to 9 further comprising the step of sorting the calculated placed laser shots.
11 . The method of any of the foregoing claims, wherein the refractive excimer laser provides a laser beam at a spot size fixed between 0.5 mm and 3.5 mm in diameter, preferably at a spot size fixed between 1.0 to 2.0 mm in diameter.
12 . An apparatus for calculating a laser shot file for use in a refractive excimer laser preferably for performing a refractive laser treatment of an eye or for producing a customized contact lens or an intraocular lens comprising means for providing information with respect to a desired ablation profile, means for calculating a shot density for obtaining the desired ablation profile, means for determining a grid width of a grid being used for placing laser shots of the excimer laser on grid positions wherein the grid width is determined based on the calculated shot density of the desired ablation profile.
13 . The apparatus of claim 12 , wherein the grid width is determined such that within a treatment zone a minimum number of grid positions receive one laser shot in sub-areas where the calculated shot density is low and/or such that a maximum number of grid positions receive one laser shot in sub-areas where the calculated shot density is high.
14 . The apparatus of claim 13 , wherein within the treatment zone the minimum number of grid positions in sub-areas where the calculated shot density is low is at least 4 percent, preferably at least 10 percent and more preferably at least 20 percent of grid positions in said sub-areas where the calculated shot density is low.
15 . The apparatus of claim 13 or 14 , wherein within the treatment zone the maximum number of grid positions in sub-areas where the calculated shot density is high is not more than 96 percent, preferably not more than 90 percent and more preferably not more than 80 percent of grid positions in said sub-areas where the calculated shot density is high.
16 . The apparatus of any of claims 12 to 15 , wherein the grid width G is determined by using the equation
G =√{square root over ( V Shot *D max ( x, y )/ z max ( x, y ))}{square root over ( V Shot *D max ( x, y )/ z max ( x, y ))}.
wherein
V Shot is the ablation volume of a single laser shot,
D max (x, y) is the local maximum shot density at a grid position P(x,y),
z max (x, y) is the maximum value of the ablation profile at the grid position P(x,y).
17 . The apparatus of any of claims 12 to 16 further comprising means for calculating the placement of the laser shots of the excimer laser on grid positions using a dither algorithm.
18 . The apparatus of claim 17 further comprising means for deciding for each grid position whether to place a laser shot or not by using a cost function of the dither algorithm.
19 . The apparatus of claim 18 wherein the means for deciding whether to place a shot on a given grid position receives information of a corresponding decision with regard to the grid positions in the neighborhood of the given grid position.
20 . The apparatus of any of claims 12 to 19 further comprising means for dividing a desired ablation profile into at least two ablation sub-profiles, calculating the shot density of each of said ablation sub-profiles, wherein said means for determining a grid width receives the respective calculated shot density of each of the ablation sub-profiles and determines the respective grid width.
21 . The apparatus of any of claims 17 to 20 further comprising means for sorting the calculated placed laser shots.
22 . The apparatus of any of claims 12 to 21 , wherein the refractive excimer laser provides a laser beam at a spot size fixed between 0.5 mm and 3.5 mm in diameter, preferably at a spot size fixed between 1.0 to 2.0 mm in diameter.