Abstract
Purpose :
Smoother surfaces after laser vision correction have been widely accepted as a factor for improving visual recovery regardless of the used technique (PRK, LASIK, or even SMILE). We tested the impact of laser beam truncation and dithering on residual smoothness after PMMA ablations, using a close-to-Gaussian beam profile.
Methods :
A modified SCHWIND AMARIS system has been used providing a beam profile with the following characteristics: FWHM=540µm, N=1,27, 1050Hz. The pulse energy has been optimized following Biomed. Opt. Express 4, 1422-1433 (2013), other parameter have been optimized following Invest. Ophthalmol. Vis. Sci. 2017;58(4):2021-2037. For the PMMA ablations, two configurations (with a 700µm pinhole and 760µJ and without pinhole and 870µJ (for both fluence 325mJ/cm2 and spot volume 180pl)) were considered, along with two types of lattices (with and without ordered dithering to select the optimum pulse positions). Real ablations on PMMA (ranging from -12D to +6D with and without astigmatism) completed the study setup. The effect of the 2x2 different configurations was analyzed based on the roughness in ablation estimated from the root mean square error in ablation.
Results :
Open based on the test cases. In general,
Conditions @350mJ/cm2
700µm pinhole and 760µJ energy No pinhole and 870µJ energy
Heuristic reticular search Baseline (100% residual roughness) -30%
Ordered dithering search -15% -40%
Truncation of the beam is negatively associated to a higher level of residual roughness
Ordered dithering to select the optimum pulse positions is positively associated to a lower level of residual roughness
The negative effect of severe truncation has more impact than the positive impact of ordered dithering
So that,
Minimum (or no) truncation of the beam is essential to minimize residual roughness after ablation
Dithering approaches help to further minimize residual roughness after ablation
Conclusions :
The proposed model can be used for optimization of laser systems used for ablation processes at relatively low cost and would directly improve the quality of results. Minimum (or no) truncation of the beam is essential to minimize residual roughness after ablation. Ordered dithering helps to further minimize residual roughness after ablation. Other more complex dithering approaches may further contribute to minimize residual roughness after ablation.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.