Optimum Laser Beam Characteristics for Achieving Smoother Ablations in Laser Vision Correction

Verma, Shwetabh; Hesser, Juergen; Arba-Mosquera, Samuel

doi:10.1167/iovs.16-21025

Cited by 10 publications

(13 citation statements)

References 56 publications

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“…The maximum ablation depth D max per shot (in μm) increases logarithmically with the peak fluence F p according to the following equation D max = ( 1 / ∝ ) · ln nobreak0em.25em⁡ prefix− ( F p / F t h ) where α is the spectral absorption coefficient. Figure shows how the laser ablation spots, and the associated ablation craters, are directly linked to the super-Gaussian orders n (○) and n (□).…”

Section: Resultsmentioning

confidence: 99%

“…The contraction approach is frequently applied in applications such as those encountered in industrial micro-machining, laser vision correction, dentistry, etc., to generate a high-quality surface finish. Most of these applications use laser devices with a Gaussian beam profile and optimized laser ablation conditions retrieved from geometrical modeling. − Such a computational approach directly relates the area illuminated by the beam to the surface topography and induced roughness via spot-related 3D laser ablation crater geometries. ,,, The conditions computationally optimized for these non-analytical applications refer in general to grid geometry, spot geometry, feed speed, etc.…”

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confidence: 99%

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Exploring the Benefits of Ablation Grid Adaptation in 2D/3D Laser Ablation Inductively Coupled Plasma Mass Spectrometry Mapping through Geometrical Modeling

et al. 2023

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This study aims to investigate the potential benefits of adapting the ablating grid in two-dimensional (2D) and threedimensional (3D) laser ablation inductively coupled plasma mass spectrometry in a single pulse mapping mode. The goals include enhancing the accuracy of surface sampling of element distributions, improving the control of depth-related sampling, smoothing the post-ablation surface for layer-by-layer sampling, and increasing the image quality. To emulate the capabilities of currently unavailable laser ablation stages, a computational approach using geometrical modeling was employed to compound square or round experimentally obtained 3D crater profiles on variable orthogonal or hexagonal ablation grids. These grids were optimized by minimizing surface roughness as a function of average ablation depth, followed by simulating the post-ablation surface and related image quality. An online application (https://laicpms-apps.ki.si/ webapps/home/) is available for users to virtually experiment with contracting/expanding orthogonal and hexagonal ablation grids for generic 3D super-Gaussian laser crater profiles, allowing for exploration of the resulting post-ablation surface layer roughness and depth.

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Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 99%

Exploring the Benefits of Ablation Grid Adaptation in 2D/3D Laser Ablation Inductively Coupled Plasma Mass Spectrometry Mapping through Geometrical Modeling

et al. 2023

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“…Along with obtaining a required corneal profile, the corneal surface quality in the ablation zone is of great importance [13][14][15].…”

Section: The Correction System Operating Principle and The Study Resultsmentioning

confidence: 99%

Expanding of Excimer Laser Photoablation’s Functionality in Ophthalmology

Алексеев

Kostin²,

Usoltseva

et al. 2021

Prib. metody izmer.

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One of the significant weaknesses of excimer laser-based vision correction devices is the difficulty of achieving a required change in the refractive properties of the cornea to sharply focus the image on the retina with distance from the working area (ablation zone) center to the periphery due to a change in the laser beam incidence angle. The study is aimed at improving the quality of laser action on the eye cornea by introducing an optical corrective system into the existing excimer laser vision correction equipment, ensuring the coincidence of the direction of the laser beam incidence on the corneal surface with the normal.It has been shown that the greater the reflection coefficient, the lower the absorbed energy, and the shallower the laser radiation penetration and ablation depths, which reduces the laser action opportunities and quality. When using excimer laser vision correction devices, it has been proposed to change the angle of the laser beam incidence on the cornea with a distance from the working area (ablation zone) center to the periphery during the surgery by introducing an optical corrective system based on a lightweight controllable and movable mirror, which allows achieving the coincidence of the direction of the laser beam incidence on the corneal surface with the normal.The studies have shown that the coincidence of the laser beam incidence on the corneal surface at any point with the normal when using a priori data on the specifics of the patient's eye allows expanding the functional opportunities of excimer laser photoablation, i. e., expand the ablation zone by 30 % and eliminate the possibility of errors caused by the human factor. The technique proposed can be used for excimer laser vision correction according to PRK, LASIK, Femto-LASIK, and other methods. To implement this approach, a patented excimer laser vision correction unit has been proposed with a PCcontrolled optical shaping system comprising galvo motor platforms and galvo mirrors installed on them.

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“…The lasers used in micromachining are normally pulsed excimer lasers, where the duration of the pulses is very short compared to the time period between the pulses. Despite attempts for achieving high levels of ablation smoothness 18,19,20,21 laser corneal refractive surgery still presents some challenges in terms of the residual roughness associated with the cornea postoperatively (Figure 1 20 ). This residual roughness may influence the epithelium to respond in a way that produces haze, regression and reduced accuracy of refractive correction, to degrade overall visual performance 22 .…”

Section: Called Visualmentioning

confidence: 99%

Method for assessing the impact of residual roughness after corneal ablation simulated as random and filtered noise in polychromatic vision

Verma¹,

Hesser²,

Arba-Mosquera³

2023

J. Eur. Opt. Society-Rapid Publ.

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Purpose: Despite theoretical models for achieving laser-based ablation smoothness, methods do not yet exist for assessing the impact of residual roughness after corneal ablation, on retinal polychromatic vision. We developed a method and performed an exploratory study to qualitatively and quantitatively analyze the impact of varying degree of corneal roughness simulated through white and filtered noise, on the retinal image. Methods: A preliminary version of the Indiana Retinal Image Simulator (IRIS) (J Opt SocAm A Opt Image SciVis. 2008 Oct;25(10):2395-407) was used to simulate the polychromatic retinal image. Using patient-specific Zernike coefficients and pupil diameter, the impact of different levels of chromatic aberrations was calculated. Corneal roughness was modeled via both random and filtered noise (Biomed. Opt. Express 4, 220-229 (2013)), using distinct pre-calculated higher order Zernike coefficient terms. The outcome measures for the simulation were simulated retinal image, Strehl Ratio and Visual Strehl Ratio computed in frequency domain (VSOTF). The impact of varying degree of roughness (with and without refractive error), spatial frequency of the roughness, and pupil dilation was analyzed on these outcome measures. Standard simulation settings were pupil size = 6mm, Defocus Z[2,0] = 2 μm (-1.54D), and Spherical Aberrations Z[4,0] = 0.15 μm. The signal included the 2-4th Zernike orders, while noise used 7-8th Zernike orders. Noise was scaled to predetermined RMS values. All the terms in 5th and 6th Zernike order were set to 0, to avoid overlapping of signal and noise. Results: In case of a constant roughness term, reducing the pupil size resulted in improved outcome measures and simulated retinal image (Strehl = 0.005 for pupil size = 6mm to Strehl = 0.06 for pupil size = 3mm). The calculated image quality metrics deteriorated dramatically with increasing roughness (Strehl = 0. 3 for no noise; Strehl = 0.03 for random noise of 0.25µm at 6mm diameter; Strehl = 0.005 for random noise of 0.65µm at 6mm diameter). Clear distinction was observed in outcome measures for corneal roughness simulated as random noise compared to filtered noise, further influenced by the spatial frequency of filtered noise. Conclusion: The proposed method enables quantifying the impact of residual roughness in corneal ablation processes at relatively low cost. Since normally laser ablation is an integral process divided on a defined grid, the impact of spatially characterized noise represents a more realistic simulation condition. This method can help comparing different refractive laser platforms in terms of their associated roughness in ablation, indirectly improving the quality of results after Laser vision correction surgery.

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Optimum Laser Beam Characteristics for Achieving Smoother Ablations in Laser Vision Correction

Cited by 10 publications

References 56 publications

Exploring the Benefits of Ablation Grid Adaptation in 2D/3D Laser Ablation Inductively Coupled Plasma Mass Spectrometry Mapping through Geometrical Modeling

Exploring the Benefits of Ablation Grid Adaptation in 2D/3D Laser Ablation Inductively Coupled Plasma Mass Spectrometry Mapping through Geometrical Modeling

Expanding of Excimer Laser Photoablation’s Functionality in Ophthalmology

Method for assessing the impact of residual roughness after corneal ablation simulated as random and filtered noise in polychromatic vision

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