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AIM: To determine the corneal sensitivity recovery period after laser-assisted sub-epithelial keratectomy (LASEK) refractive surgery and investigate the effects of ablation depth on it. METHODS: In this study examinations were performed on 90 right eyes of 90 people (34 males and 56 females) with an age range of 20-35 and an average of 22.26±3.8 years old. A sensation of 5 corneal regions, including the center and 4 mid-peripheral regions, i.e., nasal, inferior, temporal, and superior, each at a distance of 2 mm from the center of the cornea were measured with a Cochet-Bonnet esthesiometer device in 3-time points including before LASEK, 1 and 3mo after the surgery, respectively. LASEK was performed on individuals with stabilized myopia of -1.00 to -7.00 diopters and astigmatism of less than 2.00 diopters. Furthermore, the individuals were divided into three groups regarding ablation depth. RESULTS: The highest level of corneal sensitivity before surgery was related to the center of the cornea (59.1±7.76), and the highest level of corneal sensitivity loss was also related to this region. The sensation of all measured corneal regions significantly reduced 1mo postoperatively and returned to their preoperative levels 3mo after surgery (mean of 5 corneal regions in levels of preoperation: 58.2±6.48, 1mo postoperation: 57.3±5.84, 3mo postoperation: 58.2±5.49; P

A finite element model of nanosecond laser interaction with the Cu-Al2O3 dispersion strengthened alloys has been established according to the underlying mechanism of melting flow, phase transition, and evaporation removal of material. Attempting to replicate the multi-field coupling effects in laser ablation process, this model takes both the thermophysical properties of materials varied with the temperature, and the evolution of erosion morphology under the instantaneous high-temperature action of pulsed laser into consideration. Moreover, the influence of coaction of diverse forces (including recoil pressure, surface tension, and Marangoni force), the phase transformation, and the melting flow of material on the laser processing were also integrated into the model. On the basis of the proposed model, a FEM simulation study on the distribution of temperature field, formation process of erosion morphology, and numerical prediction of ablation depth in laser processing was performed. The deviation of the predicted values of ablation depth from the experimental results under the same power condition as the simulations can be controlled within 13%, indicating that the proposed simulation model can be adopted to effectively predict the width of heat affected zone (HAZ) and the width of recast layer under specific processing parameters. [ABSTRACT FROM AUTHOR]

Mansour M Al-Mohaimeed Department of Ophthalmology, College of Medicine, Qassim University, Qassim, Kingdom of Saudi ArabiaCorrespondence: Mansour M Al-Mohaimeed, Email ma.almohaimeed@qu.edu.saPurpose: This study investigated the effect of prophylactic mitomycin C (MMC) on corneal endothelium to inhibit corneal haze formation post transepithelial photorefractive keratectomy (T-PRK).Methods: A total of 120 eyes of 60 patients with low, moderate, and high myopia were subjected to T-PRK with intraoperative application of MMC (0.02%) for 30– 50s. Patients’ files were categorized into three groups according to ablation depths (if ≥ 100 μm) during T-PRK as follows: (1) Group A – low myopia without MMC, (2) Group B – low myopia with MMC, and (3) Group C – moderate/high myopia with MMC. Preoperative/surgical parameters and refractive outcomes were documented. Cell density (CD), number of cells (NUM), coefficient of variation, central corneal thickness (CCT), hexagonality (HEX/6A), average cell area (AVG), and its standard deviation (SD) were evaluated using specular microscopy preoperatively and postoperatively.Results: Overall, 119 out of 120 eyes showed significant prevention of corneal haze. Groups A and C showed no significant changes in endothelial CD and NUM. Group B showed a non-significant reduction in CD. However, all three groups showed significant variations in HEX/6A, CCT, AVG, and SD.Conclusion: The MMC application did not significantly affect corneal endothelial density or number and can be used safely and effectively to prevent corneal haze following T-PRK in myopia.Keywords-: ablation depth, corneal endothelium, corneal haze, mitomycin C, transepithelial key photorefractive keratectomy

Micromachining of ceramics is a challenging task for industries due to high hardness property but has many applications in the modern engineering world. Laser micromilling is a popular technique to enhance machining efficiency and surface quality attributes of ceramics. In current work, laser micromilling is investigated in different gas medium(s) (dry air, Ar, N2) with a nanosecond laser to improve the machining characteristics of SiAlON ceramic. Laser micromilling is investigated along five factors: axial feed; scanning velocity; pulse repetition rate (PRR); assist gas medium; and laser path scanning strategy with ablation depth; and material removal rate (MRR) as responses. A Taguchi L27 orthogonal experiment design was used for experimentation. The factor contribution based on analysis of variance (ANOVA) shows assist gas to be most significant for ablation depth with contribution of 34.57%; whereas, for MRR, it is 9.91%. The scanning strategy contributed most for MRR with 60.53%. The optimum conditions for maximum ablation depth are axial feed of 10 µm, PRR of 50 kHz and scanning velocity of 15 mm/s; and for MRR are axial feed of 20 µm, PRR of 50 kHz and scanning velocity of 40 mm/s. Dry air and triangular scan strategy are found to be optimum for both responses. Lastly, a surface morphology study shows redeposition and recasts with minor cracks on surface due to thermal stress in Ar and N2 medium. [ABSTRACT FROM AUTHOR]

The parts of engineering machinery quickly generate rusty oxides in the working process, which seriously affects their service life and safety. How to remove oxides efficiently without damaging the surface of the matrix is a crucial problem. This paper analyzes the critical laser parameters that affect the distribution of material temperature field, which determines the ablation depth of different oxides, by using the central composite experimental design method and taking the surface-ablation depth of Fe2O3 and Fe3O4 before and after laser cleaning as response variables to establish the prediction model of single removal volume with the help of Comsol Multiphysics software. The results show a positive correlation between ablation depth and peak power density and a negative correlation with scanning speed. In this process, the experimental results show that the prediction model is natural and effective. A flow chart of laser stepwise cleaning of layered corroded oxides can provide theoretical guidance for the laser cleaning of engineering machinery. [ABSTRACT FROM AUTHOR]

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Modeling and simulation of laser-matter interaction with aluminum thin film on silicon substrate is conducted using a 1D radiation hydrodynamics code, known as HYADES. Various physical processes at the microscopic/atomic level during laser-matter interaction including laser deposition, ionization, thermal energy transport, and hydrodynamics motion are considered in the model. To validate the numerical model, single pulse laser irradiation experiments are conducted. Cross sectional profiles of the ablation sites are characterized, and ablation depths are extracted from the profiles. The numerical model is verified by comparing model predictions with experimental results. The validated model will be used in the future to study the effects of various laser parameters (e.g., laser fluence, pulse duration, laser wavelength, pulse train) on ablation efficiency and quality (e.g., ablation depth, heat affected zone). [ABSTRACT FROM AUTHOR]

Results of experiments on ablation of targets made of stainless steel and aluminum with a scanning beam of nanosecond pulses at a power density of up to q = (0.38–1.0) × 109 W/cm2 are presented. The overlap of the impact zones during irradiation was found to lead to an increase in the ablation depth in proportion to the area of irradiation spot overlap. This effect is due to fact that, as the degree of overlap of irradiation spots increases, zones with a larger number of pulsed-irradiation effects are formed on the target surface, which increases the melt bath depth and leads to the ejection of larger particles. The aluminum ablation depth increases with the increase in the interpulse interval up to Δt = 10 ms; the larger the overlap of irradiation spots, the more significant the increase. The shape of the ejected particles changes from spherical, characteristic of the particles produced from a melt, to an irregular shape, which is characteristic of the particles produced as a result of mechanical destruction of the target by an internal shock wave. The size and velocity distributions of the ejected particles were determined, and the data obtained were used to calculate the shielding coefficients for laser radiation as a function of the degree of overlap of irradiation spots. It was found that the main mechanism that drives the decrease in the efficiency of the ablation with a scanning radiation beam is the reverse flux of microparticles that are deposited on the target surface. The energy balance of the ablation of aluminum has been analyzed. [ABSTRACT FROM AUTHOR]

PurposeTo compare the predicted ablation depth (AD) with the postoperatively measured corneal ablation depth (postop-AD) at central, paracentral, and midperipheral locations using two rotating Scheimpflug analyzers and a Fourier-domain optical coherence tomographer in eyes that underwent femtosecond laser-assisted LASIK (FS-LASIK).MethodsThe values of corneal thickness were measured preoperatively and postoperatively at one and three months. The difference between preoperative and postoperative was defined as postop-AD. Measurements were performed at the corneal vertex and mid-peripheral area. The mid-peripheral corneal thickness was measured at the superior, inferior, nasal, and temporal locations at a distance of 1.0 or 2.5 mm from the corneal vertex. The predicted AD was calculated by ORK-CAM software (Schwind eye tech-solutions GmbH, Kleinostheim, Germany), and the difference between the predicted AD and postop-AD was defined as Δ-AD. Paired t-test analysis was employed to evaluate the differences, agreement was assessed by the Bland-Altman method.ResultsForty-two eyes of 42 patients were investigated. At one month, the predicted AD in the central and paracentral areas was underestimated by the Pentacam HR (Oculus, Wetzlar, Germany), Sirius (Costruzione Strumenti Oftalmici, Florence, Italy) and RTVue OCT (Optovue Inc., Freemont, CA, United States), whereas Δ-AD was negative as established by all devices and predominantly statistically significant. The Δ-AD values approximated zero at three months. The mean difference of Δ-AD at three months at the corneal vertex was 0.67 ± 9.39 mm, −7.92 ± 9.05 mm and −1.36 ± 8.31 mm, respectively. The mid-peripheral measurements had positive values at one month and even more highly positive at three months (with statistically significant differences in most of the cases). The agreement between the predicted and postop-AD was moderate with all devices, but slightly better with RTVue.ConclusionThe predicted AD seems to be underestimated in the central and paracentral corneal area and overestimated in the mid-periphery.Translational RelevanceThe study could help to partly explain and prevent the refractive errors after FS-LASIK.

Purpose: The aim of this study was to correlate ablation depth on corneal endothelial cell (EC) indices following transepithelial photorefractive keratectomy (TPRK) in Saudi myopic patients., Methods: This was a retrospective cohort study of myopic eyes treated with TPRK. The changes in EC density and other indices were noted one week (W1) and 12 weeks (W12) after TPRK, which was the primary outcome. The laser ablation depth (AD) was correlated to the EC indices. The preoperative factors were also correlated to the outcomes using regression analysis to review predictors of change in the EC density., Results: We had 120 eyes of 60 myopic patients operated on for TPRK. The mean of maximum AD (Adm) and central AD (ADc) were 110.3±23.7 µ and 108.8±24.4 µ, respectively. The median change in EC count at W1 and W12 were -9.5 (interquartile range (IQR) -33.0, 17.0) and -3.0 (IQR -29.3, 13.3), respectively. The ADm was negatively correlated to a change in EC density at W1 (Wilcoxon (Z) =-2.7, P = 0.006) and at W12 (Z = -3.74, P <0.001). ADm (Kruskal-Wallis (K-W) test (P) = 0.167), ADc (K-W P = 0.08), central corneal thickness (K-W P = 0.65), and use of mitomycin-C (K-W P = 0.357) were not significant predictors of the change in EC density at W1. None of the variables significantly influenced the change in EC density at W12., Conclusions: The corneal ablation depth for TPRK is correlated to changes in EC density at W1 and W12 after TPRK., Competing Interests: Human subjects: Consent was obtained or waived by all participants in this study. Animal subjects: All authors have confirmed that this study did not involve animal subjects or tissue. Conflicts of interest: In compliance with the ICMJE uniform disclosure form, all authors declare the following: Payment/services info: All authors have declared that no financial support was received from any organization for the submitted work. Financial relationships: All authors have declared that they have no financial relationships at present or within the previous three years with any organizations that might have an interest in the submitted work. Other relationships: All authors have declared that there are no other relationships or activities that could appear to have influenced the submitted work., (Copyright © 2024, Alrashidi et al.)

The current transmission and reflection laser ablation micropropulsion modes have the problem of a complex working medium supply system in engineering. Therefore, we propose large-spot laser ablation with a one-dimensional supply mode. In order to verify this ablation mode, a multipulse ablation experiment of submillimeter-scale light spots was carried out on the surface of pretreated copper and nickel under the atmosphere using an ultrafast laser with a pulse width of 290 fs and 10 ps. The results show that femtosecond laser multipulse ablation (FLMA) leads to the grain refinement of copper, the crater quality of the two metals under FLMA is better, and picosecond laser multipulse ablation (PLMA) causes the crater of nickel to form a dense remelting bulge that affects laser absorption; both metals have obvious heat-affected zones after FLMA and PLMA, the heat-affected zones of nickel are 5–10% larger than those of copper, and the ablation depth of copper is deeper. Under the same conditions, the ablation mass of copper is smaller than that of nickel, and the specific impulse performance of laser ablation micropropulsion is better.

The parts of engineering machinery quickly generate rusty oxides in the working process, which seriously affects their service life and safety. How to remove oxides efficiently without damaging the surface of the matrix is a crucial problem. This paper analyzes the critical laser parameters that affect the distribution of material temperature field, which determines the ablation depth of different oxides, by using the central composite experimental design method and taking the surface-ablation depth of Fe2O3 and Fe3O4 before and after laser cleaning as response variables to establish the prediction model of single removal volume with the help of Comsol Multiphysics software. The results show a positive correlation between ablation depth and peak power density and a negative correlation with scanning speed. In this process, the experimental results show that the prediction model is natural and effective. A flow chart of laser stepwise cleaning of layered corroded oxides can provide theoretical guidance for the laser cleaning of engineering machinery.

To evaluate the agreement between the predicted and measured central corneal thickness (CCT) reduction after the small incision lenticule extraction (SMILE) surgery and femtosecond laser-assisted in situ keratomileusis (FS-LASIK) surgery. A total 165 patients were enrolled in this prospective study. Eighty patients with a mean spherical equivalent (SE) of −4.72 ± 1.80 Diopters (D) were treated with the FS-LASIK procedure and Eighty-five patients with a mean SE of −4.78 ± 1.63 D were treated with SMILE procedure. One eye for each patient was randomly selected and included for statistical analysis. Ultrasound pachymetry measurement and Scheimpflug camera corneal topography were performed preoperatively and 3 months postoperatively. The measured CCT reduction was calculated by comparing the preoperative examinations with postoperative examinations. Comparative statistics and linear regression analyses were performed. The mean predicted CCT reduction was 95.02 ± 21.39 μm in FS-LASIK group and 103.49 ± 22.87 μm in SMILE group (P =.015). The prediction of laser platform was found to overestimate the measured CCT reduction for both FS-LASIK group (ultrasound 13.20 ± 9.34 μm) and SMILE group (ultrasound 13.12 ± 8.68 μm). The prediction of laser platform was found to systematically overestimate the measured CCT reduction in FS-LASIK group. In SMILE group, the difference between predicted and measured CCT reduction were found significantly related with the predicted CCT reduction (P <.001 for ultrasound; and P =.004 for Pentacam). A systematic overestimation of measured CCT reduction in FS-LASIK group did not influence the refractive precision of FS-LASIK. Due to the different biomechanical distributions in post-SMILE cornea, the measured CCT reduction was influenced as the changes in refractive correction. Nomogram adjustment for high myopic correction needs further research. [ABSTRACT FROM AUTHOR]

AIM: To investigate the changes of corneal epithelial thickness following small incision lenticule extraction(SMILE), and its relationship with the ablation depth, spherical equivalent and optical zone. METHODS: Sixty-one myopic patients with or without astigmatism who underwent SMILE in our hospital from August 2017 to November 2017 were selected. RTvue-OCT was performed before surgery, 1wk, 1mo and 6mo after surgery, respectively, and the corneal epithelial thickness of patients were measured. The changes of corneal epithelial thickness following small incision lenticule extraction(SMILE), and its relationship with the ablation depth, spherical equivalent and optical zone were studied.RESULTS: There was no statistically significant difference in the thickness of corneal epithelium among the three regions(central corneal region, para-central corneal region and peripheral region)before surgery(P>0.05). Compared with the baseline values before surgery, the thickness of corneal epithelium in the three areas was significantly thickened 1wk, 1mo and 6mo after surgery(PCONCLUSION: The corneal epithelial thickness increases after SMILE in different regions, and the thickening value was positively correlated with the spherical equivalent, ablation depth.

This paper reports the effect of Ti:Sapphire laser (800 nm, 30 fs) fluence on the surface morphology, ablated area, ablation rate and hardness of a femtosecond laser irradiated Zn in air and ethanol. Targets were exposed to 1000 succeeding pulses at various fluences ranging from 1.3 to 5 J cm−2. To characterize the growth of structures on the surface of irradiated Zn, Field Emission Scanning Electron Microscopy (FESEM) has been performed. The ablation depth has been measured using a confocal microscope. Nonuniform surface morphology with an appearance of both micro and nanoscale droplets, particulates and rims has been observed in case of air-assisted ablation, whereas, in ethanol, nanoscale colloids, droplets, pores and bowl-shaped cavities have been formed. The ablation of Zn in air is responsible for deep craters with pronounced melt expulsions and ripples. Whereas, shallow and clean craters are formed in ethanol. The ablation threshold fluence is evaluated analytically and experimentally by employing three methods, i.e., squared diameter, depth ablation rate, and volume ablation rates. The hardness of irradiated targets is higher as compared to untreated Zn and shows an increasing trend with increasing fluence for both environments. However, in the case of ethanol, the hardness values are higher than air. [ABSTRACT FROM AUTHOR]

The characterization of molten corium–concrete interaction (MCCI) has increasingly become a cause of concern because, in the case of a severe nuclear accident, the core could meltdown and release radiation into the environment. The objective of this study was to determine the thermochemical impact of metal content in the corium and analyze the effect of corium metal content on ablation depth, corium temperature, its viscosity and surface heat flux, and production of hydrogen, carbon monoxide, and carbon dioxide. The governing heat transfer equations were solved while considering the various thermochemical reactions in the existing numerical code in a comprehensive way. The developed MCCI model in CORQUENCH was validated against the data available in the literature. Our findings showed that the composition of corium, especially its metal content, has a noticeable effect on mitigating or aggravating the ablation depth and nuclear reactor integrity. We observed that during molten corium–concrete interaction, zirconium plays a significant role and its presence can increase the ablation depth exponentially from 18.5 to 139 cm in the investigated case study. It was found that the presence of zirconium in the corium instigated various thermochemical reactions continuously, and thus the injected water, instead of quenching the molten corium, enhances the temperature by facilitating exothermic reactions. Additionally, due to the presence of zirconium, the production of hydrogen and carbon monoxide increases by 45 and 52 times, respectively and the generation of carbon dioxide becomes zero because the zirconium reacts with carbon dioxide continuously, converting it to carbon monoxide.

Ablation dynamics focusing exclusively on the thermal field without also considering electron emission and thermal stress is incomplete. The thermo-elasto-plastodynamic model developed in Part I of the paper is applied to estimate non-thermal ablation and the onset of fracture in a polycrystalline gold material in response to ultrafast irradiation of low fluence. Non-thermal ablation in the polycrystalline gold material is a complex dynamical process involving incident fluence, material thermophysical properties, and grain size as the primary parameters. Lattice temperatures are found to be persistently lower than the melting temperature of the target material, thus implying material removal, i.e., ablation, by ways of phase transition and phase explosion is physically improbable. The mechanism that underlies thermally induced damage modes such as yielding, layer disintegration, fragmentation, fracture, and ejection is investigated by exploring the induced thermal stress, elastic-plastic deformation, and strain energy density rate. The concept of power density is applied to estimate ablation depth and the time instance at which yielding and subsequent non-thermal ablation are initiated. [ABSTRACT FROM AUTHOR]

Purpose: To evaluate corneal biomechanical changes and their correlation with the percentage of tissue altered (PTA) in myopic femtosecond (FS)-flap LASIK.Methods: Prospective longitudinal observational study of 80 eyes of FS LASIK. Demographic details, LASIK parameters, preoperative and postoperative (day 1, month 1, 3, and 6), UCVA, BCVA, refraction, corneal topography, corneal hysteresis (CH), and a corneal resistance factor (CRF) were noted. Change in CH and CRF and its correlation with PTA were analyzed. Data were analyzed in three subgroups [subgroup 1: PTA 23 to <27%; subgroup 2: 27 to <33%; subgroup 3: 33 to <40%].Results: FS LASIK for MRSE -3.5D ± 1.6D with mean PTA of 31.6 ± 4.4% (range 23.8-39.8%), showed statistically significant decrease in CH and CRF. Mean CH decreased from a preoperative value of 10.4 ± 1.9 to 8.1 ± 1.1; mean CRF from 10.5 ± 1.6 to 7.5 ± 1.3 at 6-months postoperative period, respectively. Mean preoperative CH decreased by 25%, 24%, 23%, and 21% and mean preoperative CRF decreased by 34%, 28%, 28%, and 28% at postoperative day 1, month 1, 3, and 6 follow-ups. Mean CH and CRF showed a significant negative correlation with PTA (CH: r = - 0.33 [P = <0.0001], CRF: r = -0.34 [P = <0.001]. Subgroup analysis noted greater decrease in CRF and CH in eyes with higher PTA (subgroup 3).Conclusion: Myopic FS LASIK causes a decrease in corneal biomechanics with a significant negative correlation with PTA indicating a greater decrease in corneal biomechanics with higher PTA. [ABSTRACT FROM AUTHOR]

Single point laser ablation of Si 3 N 4 under dry and water medium is investigated and analysed. The experiments were conducted based on the one-factor-at-a-time strategy considering various input parameters such as piercing time, focus point position and water layer thickness. The effects of process inputs on the ablated hole's geometrical features including the ablation depth and diameter, hole taper, and hole edge roundness under presence and absence of water as an intermediate medium are studied. The laser focus point position was determined and varied during the investigation. It was found that, compared to the dry condition, the maximum ablation depth under wet condition is much more sensitive to the position of the laser focus point. It was also observed that the ablation depth is directly influenced by the piercing time in both dry and under water conditions. Picosecond laser single point ablation under a water layer with a thickness of 0.6 mm could increase the ablation depth up to 23%, compared to the dry condition. However, the ablation depth was significantly decreased by increasing the water layer thickness. Additionally, the hole entrance edge was rounded with increasing the water layer thickness. The hole taper was significantly influenced by the water layer thickness. [ABSTRACT FROM AUTHOR]

We provide measurements of the ablation of four post-transition and transition metals [aluminum (Al), copper (Cu), nickel (Ni) and tungsten (W)] irradiated by single 800 nm laser pulses, in ultrashort regime from 100 femtosecond (fs) pulse duration down to 15 fs covering a temporal range little explored as yet. For each metal and pulse duration tested, we measured its ablation characteristics (depth and diameter) as a function of incident energy allowing us to determine its laser-induced ablation threshold and ablation rate in a single-shot regime. For all the metals studied, we observed a constant ablation threshold fluence as a function of pulse duration extending this scaling law to pulse duration of few-optical-cycles. We provide evidence of the interest of adjusting the incident fluence to maximize the energy specific ablation depth but also of the absence of any peculiar advantage related to the use of extremely short-pulse duration for ablation purposes. Those informative and detailed ablation data have been obtained in the single-pulse regime and in air ambiance. They can serve as rewarding feedback for further establishing smart strategy for femtosecond laser micromachining and laser damage handling of metallic and metal-based components as well as for enhancing accuracy of modeling of fs laser interaction with metals in ultrashort regime. [ABSTRACT FROM AUTHOR]

The availability of high power ultrafast lasers for material processing enables new applications such as deep hole drilling. To reach high ablation rates and high aspect ratios, fluences in the order of magnitude of 100 J/cm² are required. As this range has rarely been described in literature, a detailed study of the ablation rate for stainless steel is presented here. At a mean fluence of ~1.3 J/cm² a molten phase is observed in the center of the hole which then extends over the entire ablated area for increasing fluences. Due to the onset of a melt layer a melt supported ablation superimposes the anticipated second ablation regime and hence no logarithmic dependence of the ablation depth is visible for higher fluences. For fluences of 10 J/cm² and higher the entire area is subject to a melt supported ablation. In addition, in this fluence range only the deposition of a few pulses at a higher repetition rate can boost the ablation rate up to a factor of 10 due to heat accumulation. [ABSTRACT FROM AUTHOR]

Background: The pulsed output of the 308 nm XeCl laser and its photoablation action rather than photothermal action offers the ability to remove dental hard tissues with minimal generation of heat in the tissue. Materials and Methods: A total of 20 human molar teeth (ten teeth used as enamel samples and ten teeth used as dentin samples after removing the enamel tissue from their crowns) were irradiated by the laser. The crown of each sample was regarded as a cube which its lateral sides were exposed in 2Hz frequency without water cooling. Also, 18 holes for all enamel samples and 18 holes for all dentin samples were obtained. Three different amounts of energy were selected as a variable factor with 6 different numbers of pulses in each energy. The images of these holes were prepared by optic and computer combining, and the amounts of the ablation depth and effective ablation area were calculated using the MATLAB software. Results: The amounts of ablation depth were increased with increasing the number of pulses for both enamel and dentin tissues. The amounts of ablation depth were also increased with increasing the amounts of energy for both enamel and dentin tissues. The greater amounts of ablation depth and effective ablation area were observed in the dentin tissue rather than the enamel tissue. The borders of created holes were reported sharp and clear. Conclusion: The application of the XeCl laser for hard tissue removal and cavity preparation can be possible after some certain modifications.

Introduction: The Goldmann applanation tonometer readings were noted to be markedly reduced after Lasik surgery using a thin flap technique which is widely used nowadays, to correct a wide range of myopia and astigmatism. The Ocular Response Analyzer (ORA) is considered one of the important tools for refinement of Intraocular Pressure (IOP) measurements. The aim of this study is to evaluate and refine ORA measurements for IOP changes post- M2 90 Moria microkeratome Lasik procedure for Egyptian myopic and astigmatic patients trying to aid in glaucoma diagnosis and management. Methods: Thirty-five eyes of nineteen Egyptian patients with myopia or myopic astigmatism who had undergone Lasik procedure using M2 90 Moria microkeratome were included in this consecutive case series study. All cases were subjected to full ophthalmological examination including uncorrected and best corrected visual acuity, refraction, slit lamp examination, Scheimpflug imaging and ORA (Reichert Ophthalmic Instruments, Inc., Buffalo, NY, USA). The refractive errors were measured using an auto refractometer and were confirmed by trial. For the ocular response analyzer, the Goldmann-correlated IOP measurement (IOPg) which simulates IOP measured by Goldmann tonometer and the Corneal-Compensated Intraocular Pressure (IOPcc) that takes corneal biomechanical properties into consideration were reported as well as the Corneal Hysteresis (CH) and the Corneal Resistance Factor (CRF). Cases were examined preoperatively and again about one month after Lasik, after stabilization of eye condition. The collected data were tabulated and analysed with the suitable statistical methods. The mean values and standard deviation were calculated for quantitative data. Comparison tests (t-test) and correlation tests (Pearson) were also performed. Results: In our study, involving M2 90 Moria microkeratome Lasik procedure, a highly significant post-Lasik reduction in IOPg (t-test = 8.62 (p

Objectives: The impact of skin hydration on patterns of thermal injury produced by ablative fractional lasers (AFLs) is insufficiently examined under standardized conditions. Using skin with three different hydration levels, this study assessed the effect of hydration status on microchannel dimensions generated by a fractional CO 2 laser., Methods: A hydration model (hyperhydrated-, dehydrated- and control) was established in ex vivo porcine skin, validated by changes in surface conductance and sample mass. After, samples underwent AFL exposure using a CO 2 laser (10,600 nm) at two examined pulse energies (10 and 30 mJ/mb, fixed 10% density, six repetitions per group). Histological assessment of distinct microchannels (n = 60) determined three standardized endpoints in H&E sections: (1) depth of microthermal treatment zones (MTZs), (2) depth of microscopic ablation zones (MAZs), and (3) coagulation zone (CZ) thickness. As a supplemental in vivo assessment, the same laser settings were applied to hyperhydrated- (7-h occlusion) and normohydrated forearm skin (no pretreatment) of a human volunteer. Blinded measurement of MAZ depth (n = 30) was performed using noninvasive optical coherence tomography (OCT)., Results: Modest differences in microchannel dimensions were shown between hyperhydrated, dehydrated and control skin at both high and low pulse energy. Compared to controls, hyperhydration led to median reductions in MTZ and MAZ depth ranging from 5% to 8% (control vs. hyperhydrated at 30 mJ/mb; 848 vs. 797 µm (p < 0.003) (MAZ); 928 vs. 856 µm (p < 0.003) (MTZ)), while 14%-16% reductions were shown in dehydrated skin (control vs. dehydrated at 30 mJ/mb; MAZ: 848 vs. 727 µm (p < 0.003); MTZ: 928 vs. 782 µm (p < 0.003)). The impact of skin hydration on CZ thickness was in contrast limited. Corresponding with ex vivo findings, hyperhydration was similarly associated with lower ablative depth in vivo skin. Thus, median MAZ depth in hydrated skin was 10% and 14% lower than in control areas at 10 and 30 mJ/mb pulse energy, respectively (10 mJ: 210 vs. 180 µm (p < 0.001); 30 mJ: 335 vs. 300 µm (p < 0.001))., Conclusion: Skin hydration status can exert a minimal impact on patterns of microthermal injury produced by fractional CO 2 lasers, although the clinical implication in the context of laser therapy requires further study., (© 2023 Wiley Periodicals LLC.)

Aim: To determine the corneal sensitivity recovery period after laser-assisted sub-epithelial keratectomy (LASEK) refractive surgery and investigate the effects of ablation depth on it., Methods: In this study examinations were performed on 90 right eyes of 90 people (34 males and 56 females) with an age range of 20-35 and an average of 22.26±3.8 years old. A sensation of 5 corneal regions, including the center and 4 mid-peripheral regions, i.e. , nasal, inferior, temporal, and superior, each at a distance of 2 mm from the center of the cornea were measured with a Cochet-Bonnet esthesiometer device in 3-time points including before LASEK, 1 and 3mo after the surgery, respectively. LASEK was performed on individuals with stabilized myopia of -1.00 to -7.00 diopters and astigmatism of less than 2.00 diopters. Furthermore, the individuals were divided into three groups regarding ablation depth., Results: The highest level of corneal sensitivity before surgery was related to the center of the cornea (59.1±7.76), and the highest level of corneal sensitivity loss was also related to this region. The sensation of all measured corneal regions significantly reduced 1mo postoperatively and returned to their preoperative levels 3mo after surgery (mean of 5 corneal regions in levels of preoperation: 58.2±6.48, 1mo postoperation: 57.3±5.84, 3mo postoperation: 58.2±5.49; P <0.05). A significant relationship was found between ablation depth and corneal sensitivity changes in the center and temporal regions ( P <0.05)., Conclusion: Corneal sensitivity in myopia and low astigmatism decreases after LASEK and reaches the preoperative level within 3mo. The depth of ablation during surgery affected the recovery of corneal sensitivity., (International Journal of Ophthalmology Press.)

Purpose. To study topical 0.05% cyclosporine A as an adjunct to LASIK in patients with a high percentage of altered (corneal) tissue (PAT) and, consequently, with a high susceptibility risk to the post-LASIK dry eye syndrome.Material and methods. This study included 23 patients (48 eyes) with PTA≥0.4 (40%) ((PTA=(PFT+CAD)/PCT, PFT – predicted flap thickness, CAD – calculated ablation depth, PCT – preoperative corneal thickness). The patients were divided into 2 study groups: (1) standard postoperative treatment and an additional topical 0.05% cyclosporine A (3 months preoperatively and within 1 month postoperatively) and (2) standard postoperative treatment. Instability of surface regularity index (ISRI), tear production and corneal sensitivity were estimated 90±10 days preoperatively and 30±3 days postoperatively.Results. There was no statistically significant difference in ISRI, tear production and corneal sensitivity between the study groups at initial control point of investigation 90±10 days preoperatively. In the follow-up period of 30±3 days postoperatively the dynamics to an ISRI increase, a reduction of tear production and corneal sensitivity compared to preoperative values was detected in both groups. The ISRI was significantly higher in the group 2 compared to the group 1 (0.37±0.06 and 0.28±0.07, respectively, p=0.017), the tear production was significantly lower in the group 2 compared to group 1 (11.4±2.7mm and 13.8±3.6mm, respectively, p=0.021), the corneal sensitivity was significantly lower in the group 2 compared to the group 1 (34.9±5.7mm and 48.2±6.6mm,respectively, p=0.003).Conclusion. The topical application of 0.05% cyclosporine A as an pre- and post-operative adjunct to LASIK in the patients with the high PAT value (≥0.4 (40%)) reduces a severity of symptoms of post-LASIK dry eye syndrome.

The plasma brightness cannot be used as a direct indicator of ablation depth detection by femtosecond laser was experimentally demonstrated, which led to the difficulty of depth measurement in the maching process. The tests of microchannel milling on the silicon wafer were carried out in the micromachining center in order to obtain the influences of parameters on the ablation depth. The test results showed that the defocusing distance had no significant impact on ablation depth in LAV effective range. Meanwhile, the reason of this was explained in this paper based on the theoretical analysis and simulation calculation. Then it was proven that the ablation depth mainly depends on laser fluence, step distance and scanning velocity. Finally, a research was further carried out to study the laser parameters which relate with the microchannel ablation depth inside the quartz glass for more efficiency and less cost in processing by femtosecond laser. [ABSTRACT FROM AUTHOR]

Cr12MoV cold work mold steel, which is a difficult-to-machining material, is widely used in the mold and dye industry. A picosecond pulse Nd:YVO4 laser at 1064 nm was used to conduct the study. Effects of operation parameters (i.e., laser fluence, scanning speed, hatched space and number of scans) were studied on ablation depth and quality of Cr12MoV at the repetition rate of 20 MHz. The experimental results reveal that all the four parameters affect the ablation depth significantly. While the surface roughness depends mainly on laser fluence or scanning speed and secondarily on hatched space or number of scans. For laser fluence and scanning speed, three distinct surface morphologies were observed experiencing transition from flat (Ra < 1.40 μm) to bumpy (Ra = 1.40 - 2.40 μm) eventually to rough (Ra > 2.40 μm). However, for hatched space and number of scan, there is a small bumpy and rough zone or even no rough zone. Mechanisms including heat accumulation, plasma shielding and combustion reaction effects are proposed based on the ablation depth and processing morphology. By appropriate management of the laser fluence and scanning speed, high ablation depth with low surface roughness can be obtained at small hatched space and high number of scans. [ABSTRACT FROM AUTHOR]