Experimental setup to determine the pulse energies and radiant exposures for excimer lasers with repetition rates ranging from 100 to 1050 Hz

Mrochen, Michael; Wuellner, Christian; Rose, Kristin; Donitzky, Christof

doi:10.1016/j.jcrs.2009.05.021

Cited by 14 publications

(8 citation statements)

References 36 publications

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“…A pulse energy level of 0.67 mJ was specified as a standard value for AMARIS low fluence, representing a factor of 2 in the overall range covered. Laser systems with up to ∼2-mJ pulse energy are available, 35 however, such a high metric has not been covered in our tests and related extrapolations based on our results should be made with caution, although 1.33 mJ of pulse energy in a 0.54-mm spot size represents the upper limit of energy density (∼500 mJ∕cm 2 ) in refractive surgery. A maximum change in peak corneal temperature of 6.85°C and a range of 1.55°C were observed with the controlled local frequency.…”

Section: Pulse Energymentioning

confidence: 89%

Analysis of the change in peak corneal temperature during excimer laser ablation in porcine eyes

Arba-Mosquera

Verma

2015

J. Biomed. Opt.

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The objective is to characterize the impact of different ablation parameters on the thermal load during corneal refractive surgery by means of excimer laser ablation on porcine eyes. One hundred eleven ablations were performed in 105 porcine eyes. Each ablation was recorded using infrared thermography and analyzed mainly based on the two tested local frequencies (40 Hz, clinical local frequency; 1000 Hz, no local frequency). The change in peak corneal temperature was analyzed with respect to varying ablation parameters [local frequency, system repetition rate, pulse energy, optical zone (OZ) size, and refractive correction]. Transepithelial ablations were also compared to intrastromal ablations. The average of the baseline temperature across all eyes was 20.5°C±1.1 (17.7°C to 22.2°C). Average of the change in peak corneal temperature for all clinical local frequency ablations was 5.8°C±0.8 (p=3.3E-53 to baseline), whereas the average was 9.0°C±1.5 for all no local frequency ablations (p=1.8E-35 to baseline, 1.6E-16 to clinical local frequency ablations). A logarithmic relationship was observed between the changes in peak corneal temperature with increasing local frequency. For clinical local frequency, change in peak corneal temperature was comparatively flat (r 2 =0.68 with a range of 1.5°C) with increasing system repetition rate and increased linearly with increasing OZ size (r 2 =0.95 with a range of 2.4°C). Local frequency controls help maintain safe corneal temperature increase during excimer laser ablations. Transepithelial ablations induce higher thermal load compared to intrastromal ablations, indicating a need for stronger thermal controls in transepithelial refractive procedures.

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Section: Pulse Energymentioning

confidence: 89%

Analysis of the change in peak corneal temperature during excimer laser ablation in porcine eyes

Arba-Mosquera

Verma

2015

J. Biomed. Opt.

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“…A patient treated after repair of the laser electrodes showed no central island, demonstrating the capability of the excimer laser calibration system for predicting the beam profile accurately and subsequently calibrating the system accordingly. Mrochen et al 2 performed a study on freshly enucleated bovine corneas and PMMA plates to evaluate the influence of the dynamics of the laser ablation process, including the pulse energies and radiant exposures. The shot pattern for the myopic correction was maintained during all experiments, and the pulse laser energy was adjusted to achieve equal ablation depths for all repetition rates.…”

Section: Polymethylmethacrylatementioning

confidence: 99%

“…Both materials follow a Beer-Lambert law in the range of fluences used in refractive surgery, and the number of incubation pulses (that is quantified as the number of the first pulses that do not contribute to ablation depth) 5 is <4 in PMMA and 2 in Filofocon A, above 140 mJ∕cm 2 . Above 40 pulses for Filofocon A and 70 pulses for PMMA, ablation threshold and effective absorption coefficients can be considered constant (ablation threshold ¼ 90 mJ∕cm 2 and effective absorption coefficients ¼ 36;000 cm −1 , for Filofocon A, and ablation threshold ¼ 67 mJ∕cm 2 and effective absorption coefficients ¼ 52;000 cm −1 for PMMA, respectively). It was concluded that the absence of ablation artifacts (central islands), a lower number of incubation pulses, a lower pulsenumber dependence of the ablation threshold, and a good correspondence between effective absorption coefficient and the absorption coefficient alpha estimated from spectroscopic measurements make Filofocon A a more appropriate material than PMMA for experimental models in refractive surgery and for calibration of clinical lasers.…”

Section: Filofocon Amentioning

confidence: 99%

Review of technological advancements in calibration systems for laser vision correction

Arba-Mosquera

Vinciguerra²,

Verma

2018

J. Biomed. Opt.

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Abstract. Using PubMed and our internal database, we extensively reviewed the literature on the technological advancements in calibration systems, with a motive to present an account of the development history, and latest developments in calibration systems used in refractive surgery laser systems. As a second motive, we explored the clinical impact of the error introduced due to the roughness in ablation and its corresponding effect on system calibration. The inclusion criterion for this review was strict relevance to the clinical questions under research. The existing calibration methods, including various plastic models, are highly affected by various factors involved in refractive surgery, such as temperature, airflow, and hydration. Surface roughness plays an important role in accurate measurement of ablation performance on calibration materials. The ratio of ablation efficiency between the human cornea and calibration material is very critical and highly dependent on the laser beam characteristics and test conditions. Objective evaluation of the calibration data and corresponding adjustment of the laser systems at regular intervals are essential for the continuing success and further improvements in outcomes of laser vision correction procedures.

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“…Bei Photoablation mit hoher Repetitionsrate könnte der Gewebeabtrag pro Laserpuls aufgrund eines Abschirmungseffekts durch die bei der Verdampfung des Gewebes entstehende Gaswolke im Verlauf der Behandlung reduziert werden [9]. Wir konnten durch die Untersuchungen an PMMA bestätigen, dass sich bei dem von uns untersuchten Lasersystem die Effizienz bei den beiden Ablationsfrequenzen nicht unterscheidet.…”

Section: Diskussionunclassified

“…In der letzten Zeit wurden Excimer-Laser mit hohen Repetitionsraten kommerziell verfügbar gemacht. Es besteht jedoch die Sorge, dass die Photoablation bei einem Anstieg der Ablationsfrequenz infolge photochemischer oder photothermischer Einflüsse negativ beeinflusst wird [9].…”

Section: Introductionunclassified

Einfluss unterschiedlicher Ablationsfrequenzen auf die klinischen Ergebnisse bei photorefraktiver Keratektomie unter Verwendung derselben Excimer-Laser-Plattform: Ein kontralateraler Vergleich

Tandogan

Khoramnia

Gye

et al. 2016

Klin Monatsbl Augenheilkd

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The objective of this study was to evaluate postoperative clinical outcomes of photorefractive keratectomy (PRK) using different ablation frequencies. In this prospective, contralateral eye study, 56 eyes of 28 patients with myopia or myopic astigmatism were included. PRK was performed using the MEL90 excimer laser system (Carl Zeiss Meditec, Germany). One eye of each patient was treated with a repetition rate of 250 Hz, while the other one was treated with a repetition rate of 500 Hz. The treatment pattern in the 250 Hz and 500 Hz group only differed in terms of ablation frequency; there was no difference in laser pulse energy, spot size or ablation profile. Postoperative follow-ups were at 3 and 7 days and 1, 3 and 6 months. The following parameters were assessed: Uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), higher-order aberrations (HOAs), corneal re-epithelisation time and corneal haze. Ablation depth was proportional to laser pulse counts at both frequencies. At 6 months, 100.0% of the eyes in the 250 Hz group and 96.4% in the 500 Hz group had a UDVA of 0.00 logMAR or better; 100% of the eyes in both groups were within ± 1.00D of the attempted correction. All eyes had a postoperative CDVA of 0.00 logMAR or better. There was no difference between the groups in postoperative HOAs, corneal re-epithelisation time or corneal haze. Photorefractive keratectomy with a repetition rate of 250 Hz and 500 Hz showed comparable efficacy, safety and predictability in the correction of myopia. There were no significant complications due to the high repetition rate, such as postsurgical corneal haze.

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Experimental setup to determine the pulse energies and radiant exposures for excimer lasers with repetition rates ranging from 100 to 1050 Hz

Abstract: Higher-repetition-rate excimer lasers require increased radiant exposure. Further experimental studies should be performed to determine the relevance of spatial and temporal spot positioning, ablation-plume dynamics, and temperature increases during high-repetition-rate laser treatments.

Cited by 14 publications

References 36 publications

Analysis of the change in peak corneal temperature during excimer laser ablation in porcine eyes

Analysis of the change in peak corneal temperature during excimer laser ablation in porcine eyes

Review of technological advancements in calibration systems for laser vision correction

Einfluss unterschiedlicher Ablationsfrequenzen auf die klinischen Ergebnisse bei photorefraktiver Keratektomie unter Verwendung derselben Excimer-Laser-Plattform: Ein kontralateraler Vergleich

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