Review of technological advancements in calibration systems for laser vision correction

Arba-Mosquera, Samuel; Vinciguerra, Paolo; Verma, Shwetabh

doi:10.1117/1.jbo.23.2.020901

Cited by 5 publications

(4 citation statements)

References 27 publications

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“…This represented an increase of 25 nm roughness per micron of ablation in PMMA. Many of the studies use PMMA as the ablation material of choice due the good correlation between results of laser surface profilometry scans on PMMA and clinical outcomes 40 (and its common use as a calibration material in most laser systems), however, other calibration material have been also proposed and should be equally researched for the aspect of residual roughness 41 .…”

Section: Discussionmentioning

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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Section: Discussionmentioning

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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“…Therefore, the internal compensation of SCHWIND AMARIS (preset energy, pulses) could be a factor for reducing the influence of temperature and relative humidity on PMMA ablation. In any modern commercially available refractive laser system, calibration cycles are repeated at different frequencies depending on the frequency of the system feedback [ 15 ]. In one form or another, since all laser systems follow the same principle of short-term calibration, the results of our tests on PMMA and porcine cornea, and their interrelationship would remain valid.…”

Section: Discussionmentioning

confidence: 99%

“…Since the standard PMMA test comprises of 12 different ablations [ 15 ], for each laser system the mean performance and standard deviation in all the ablations was calculated.…”

Section: Methodsmentioning

confidence: 99%

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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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Analysis of Impact of Humidity and Temperature on Excimer Laser Ablation of Polyethylene Terephthalate, Polymethylmethacrylate, and Porcine Corneal Tissue

et al. 2019

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Background and ObjectivesTo analyze the impact of humidity and temperature on excimer laser ablation of polyethylene terephthalate (PET), polymethylmethacrylate (PMMA) and porcine corneal tissue, and an ablation model to compensate for the temperature and humidity changes on ablation efficiency.Study Design/Materials and MethodsThe study was conducted using an AMARIS 1050RS (Schwind eye‐tech‐solutions) placed inside a climate chamber at ACTS. Ablations were performed on PET, PMMA, and porcine cornea. The impact of a wide range of temperature (~18°C to ~30°C) and relative humidity (~25% to ~80%) on laser ablation outcomes was tested using nine climate test settings. For porcine eyes, change in defocus was calculated from the difference of post‐ablation to pre‐ablation average keratometry readings. Laser scanning deflectometry was performed to measure refractive change achieved in PMMA. Multiple linear regression was performed using the least square method with predictive factors: temperature, relative humidity, time stamp. Influence of climate settings was modeled for pulse energy, pulse fluence, ablation efficiency on PMMA and porcine cornea tissue.ResultsTemperature changes did not affect laser pulse energy, pulse fluence (PET), and ablation efficiency (on PMMA or porcine corneal tissue) significantly. Changes in relative humidity were critical and significantly affected laser pulse energy, high fluence and low fluence. The opposite trend was observed between the ablation performance on PMMA and porcine cornea.ConclusionsThe proposed well‐fitting multi‐linear model can be utilized for compensation of temperature and humidity changes on ablation efficiency. Based on this model, a working window for optimum operation has been found (temperature 18°C to 28°C and relative humidity 25% to 65%) for a maximum deviation of ±2.5% in ablation efficiency in PMMA and porcine corneal tissue. Lasers Surg. Med. © 2019 The Authors. Lasers in Surgery and Medicine Published by Wiley Periodicals, Inc.

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Review of technological advancements in calibration systems for laser vision correction

Cited by 5 publications

References 27 publications

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

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

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

Analysis of Impact of Humidity and Temperature on Excimer Laser Ablation of Polyethylene Terephthalate, Polymethylmethacrylate, and Porcine Corneal Tissue

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