Smoothness of Ablation on Polymethylmethacrylate Plates With Four Scanning Excimer Lasers

Doga, A.V.; Shpak, A.A.; Sugrobov, V A

doi:10.3928/1081-597x-20040903-21

Cited by 12 publications

(4 citation statements)

References 5 publications

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“…Plastic models have been used in refractive surgery research and calibration for a long time, especially for the assessment of roughness and calibration of pulse energy (radiant exposure or fluence) [1,2,5,25,26]. However, it has not been until recently that plastic models have been used to study in detail the changes in the shape of the flat or spherical surfaces, after refractive surgery [27,28].…”

Section: Discussionmentioning

confidence: 99%

“…It was concluded that the laser with Scanning spot technology produced smooth ablations even up to −9.00 D. Ablation smoothness is also influenced by spot positioning algorithms. Dago et al performed ablations on PMMA plates using four scanning excimer lasers, two with flying spot technology (Zeiss-Meditec MEL-70, and a Russian-made unit, Microscan) and two Nidek models with scanning slit delivery systems and an expanding iris diaphragm (EC-5000 and EC-5000 CX) [2]. The smoothest surface was obtained in samples produced by Zeiss-Meditec MEL-70 unit (RMS = 112 ± 23 nm), followed by the Nidek EC-5000 CX (RMS = 153 ± 12 nm), and the Microscan (RMS = 181 ± 11 nm).…”

Section: Introductionmentioning

confidence: 99%

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Effect of laser beam truncation (pinhole), (ordered) dithering, and jitter on residual smoothness after poly(methyl methacrylate) ablations, using a close-to-Gaussian beam profile

Verma

Hesser

Arba-Mosquera

2021

Advanced Optical Technologies

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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, dithering (expressing a continuous profile on a basis of lower resolution causing pixels to round up/down the number of pulses to be placed), and jitter (a controlled random noise (up to ±20 µm in either direction) added to the theoretical scanner positions) on residual smoothness after Poly(methyl methacrylate) (PMMA) ablations, using a close-to-Gaussian beam profile. A modified SCHWIND AMARIS system has been used providing a beam profile with the following characteristics: close-to-Gaussian beam profile with full width at half maximum (FWHM) of 540 µm, 1050 Hz. Laser parameters have been optimized following Invest. Ophthalmol. Vis. Sci., vol. 58, no. 4, pp. 2021–2037, 2017, the pulse energy has been optimized following Biomed. Opt. Express vol. 4, pp. 1422–1433, 2013. For the PMMA ablations, two configurations (with a 0.7 mm pinhole and 0.75 mJ and without pinhole and 0.9 mJ (for fluences of 329 mJ/cm2 and 317 mJ/cm2 and corneal spot volumes of 174 and 188 pl)) were considered, along with two types of lattices (with and without ordered dithering to select the optimum pulse positions), and two types of spot placement (with and without jitter). Real ablations on PMMA (ranging from −12D to +6D with and without astigmatism of up to 3D) completed the study setup. The effect of the 2 × 2 × 2 different configurations was analyzed based on the roughness in ablation estimated from the root mean square error in ablation. 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; jitter is negatively associated to a higher level of residual roughness. The effect of dithering was the largest, followed by truncation, and jitter had the lowest impact on results. So that: Dithering approaches help to further minimize residual roughness after ablation; minimum (or no) truncation of the beam is essential to minimize residual roughness after ablation; and jitter shall be avoided to minimize residual roughness after ablation. 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 without jitter helps to further minimize residual roughness after ablation. Other more complex dithering approaches may further contribute to minimize residual roughness after ablation.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Effect of laser beam truncation (pinhole), (ordered) dithering, and jitter on residual smoothness after poly(methyl methacrylate) ablations, using a close-to-Gaussian beam profile

Verma

Hesser

Arba-Mosquera

2021

Advanced Optical Technologies

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“…The other important one is the analysis of optical results of artificial treatments on specific polymer plates. PMMA plates are widely used to test the ablation depth and to guarantee the refractive results of the excimer laser equipment from the first step of the design to the user-side daily calibration procedure [ 8 – 11 ].…”

Section: Discussionmentioning

confidence: 99%

Shielding effect of the smoke plume by the ablation of excimer lasers

et al. 2018

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BackgroundShielding and scattering effect of the smoke plume column ejected from the laser ablated material is a well-known phenomenon. Debris evacuation system of the excimer laser equipment removes these particles, but insufficient air flow can result in undesired refractive outcomes of the treatment. The aim of this study was to reveal the effect of the air flow speed on the actual ablation depth.MethodsSCWIND AMARIS 500E flying spot excimer laser was tested in this study. A 150 μm phototherapeutic keratectomy (PTK) profile with 8 mm diameter was applied to the surface of polymethyl methacrylate (PMMA) plates. The velocity of the air flow was changed with adjustable air aspiration system. Ablation depth was measured with highly-precise contact micrometer.ResultsThe prediction model was statistically significant, F(1,8) = 552.85, p < 0.001, and accounted for approximately 98.7% of variance of ablation (R2 = 0.987, R2adj = 0.986). Lower air flow speed resulted in a weaker ablation capability of the excimer laser.ConclusionAir flow generated by the aspiration equipment is a key factor for the predictable outcomes of refractive treatment. Therefore, manufacturer inbuilt debris removal system should be regularly checked and maintained to ensure proper clinical and predictable refractive results.

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“…Laser systems often utilize plastic material ablations for calibration [ 14 ] and optimization of system parameters [ 16 ]. The use of Polymethylmethacrylate (PMMA) as a calibration material has been well analyzed in the past, and used to develop comprehensive models, considering applied correction, as well as laser beam characteristics and ablative spot properties [ 17 , 18 , 19 , 20 , 21 ]. However, PMMA ablation may also be affected by the variations in temperature and humidity [ 22 , 23 ].…”

Section: Introductionmentioning

confidence: 99%

Cross Sectional Analysis of Impact of Seasonal Changes on Excimer Laser Ablation Performance on Polymethyl Methacrylate (PMMA)

Verma

Hesser

Arba-Mosquera

2023

Vision

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Seasonal changes and varying degree of corneal hydration has been linked to excimer laser corneal ablation rates. The use of PMMA as a calibration material in refractive lasers is well established. However, PMMA ablation may be equally affected by seasonal variations in temperature and humidity, in turn affecting the calibration process. The aim of this work is to analyze the effect of seasonal changes in PMMA performance using SCHWIND AMARIS laser system. PET and PMMA ablations conducted in climate-controlled environment with 826 consecutive AMARIS systems manufactured over 6 years were retrospectively analyzed. Lasers were stratified depending on seasons and months of the year. Metrics like single laser pulse fluence, nominal number of laser pulses, mean performance, standard deviation, and technical performance of system were compared to global average values. Cyclic winter–summer variation was confirmed with seasons winter and summer showing statistically significant variations with respect to global values. Metric technical performance showed deeper PMMA ablation performance in summertime, with maximum seasonal deviation of 6%. Results were consistently confirmed in seasonal as well as monthly analyses. These findings could help minimize variance among laser systems by implementing compensation factors depending on seasons such that laser systems installed worldwide follow the same trend line of variation.

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Smoothness of Ablation on Polymethylmethacrylate Plates With Four Scanning Excimer Lasers

Cited by 12 publications

References 5 publications

Effect of laser beam truncation (pinhole), (ordered) dithering, and jitter on residual smoothness after poly(methyl methacrylate) ablations, using a close-to-Gaussian beam profile

Effect of laser beam truncation (pinhole), (ordered) dithering, and jitter on residual smoothness after poly(methyl methacrylate) ablations, using a close-to-Gaussian beam profile

Shielding effect of the smoke plume by the ablation of excimer lasers

Cross Sectional Analysis of Impact of Seasonal Changes on Excimer Laser Ablation Performance on Polymethyl Methacrylate (PMMA)

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