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Inniger D, Poretti A, Ryser M, Meier C, Rathjen C, Feurer T. Corneal absorption spectra in the deep UV range. JOURNAL OF BIOMEDICAL OPTICS 2022; 27:025004. [PMID: 35220695 PMCID: PMC8881984 DOI: 10.1117/1.jbo.27.2.025004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/29/2021] [Accepted: 01/31/2022] [Indexed: 06/14/2023]
Abstract
SIGNIFICANCE Refractive surgery in ophthalmology uses pulsed lasers at 193, 210, or 213 nm. The reason is that most molecular constituents of cornea absorb strongly in this wavelength range. Precise refractive surgery via ablation requires an accurate knowledge of the absorption coefficient at the relevant wavelengths. Yet, the absorption coefficients of corneal tissue reported in literature vary by almost an order of magnitude; moreover, they were measured mostly at the wavelengths mentioned earlier. AIM By measuring the corneal absorption coefficient of intact eyeballs stored at different environmental conditions, prepared by following different procedures, and as a function of postmortem time, we determine the absorption coefficient for the entire wavelength range between 185 and 250 nm for as close as possible to in-vivo conditions. APPROACH We use a specially designed UV ellipsometer to measure refractive index and absorption coefficient. Specifically, we investigate the temporal evolution of refractive index and absorption coefficient after enucleation of the eyeballs under different environmental conditions and preparation procedures. RESULTS Our measurements provide accurate values for refractive index as well as absorption coefficient of cornea in the wavelength range between 185 and 250 nm. We find that the absorption coefficient decreases with time and that neither storage conditions nor preparation procedures but a continuous degeneration of the cornea is responsible for the observed time evolution. We use the measured time evolution to extrapolate refractive index and absorption coefficient to in-vivo conditions. CONCLUSION Our measurements of the close to in-vivo absorption coefficient of cornea between 185 and 250 nm allow for a better understanding and modeling of refractive cornea surgery, also at other than the three commonly used wavelengths. In the future, this may be relevant when new pulsed laser sources with other wavelengths become available.
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Affiliation(s)
- Dominik Inniger
- University of Bern, Graduate School for Cellular and Biomedical Sciences, Bern, Switzerland
- Bern University of Applied Science, Engineering and Information Technology, HuCE-optoLab, Biel, Switzerland
- University of Bern, Institute for Applied Physics, Bern, Switzerland
| | - Alessio Poretti
- Bern University of Applied Science, Engineering and Information Technology, HuCE-optoLab, Biel, Switzerland
| | - Manuel Ryser
- University of Bern, Institute for Applied Physics, Bern, Switzerland
| | - Christoph Meier
- Bern University of Applied Science, Engineering and Information Technology, HuCE-optoLab, Biel, Switzerland
| | | | - Thomas Feurer
- University of Bern, Institute for Applied Physics, Bern, Switzerland
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2
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Lawal RO, Donnarumma F, Murray KK. Deep-ultraviolet laser ablation electrospray ionization mass spectrometry. JOURNAL OF MASS SPECTROMETRY : JMS 2019; 54:281-287. [PMID: 30675964 PMCID: PMC6422691 DOI: 10.1002/jms.4338] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/15/2018] [Revised: 01/12/2019] [Accepted: 01/18/2019] [Indexed: 06/02/2023]
Abstract
A 193-nm wavelength deep ultraviolet laser was used for ambient laser ablation electrospray ionization mass spectrometry of biological samples. A pulsed ArF excimer laser was used to ablate solid samples, and the resulting plume of the desorbed material merged with charged electrospray droplets to form ions that were detected with a quadrupole time-of-flight mass spectrometer. Solutions containing peptide and protein standards up to 66-kDa molecular weight were deposited on a metal target, dried, and analyzed. No fragmentation was observed from peptides and proteins as well as from the more easily fragmented vitamin B12 molecule. The mass spectra contained peaks from multiply charged ions that were identical to conventional electrospray. Deep UV laser ablation of tissue allowed detection of lipids from untreated tissue. The mechanism of ionization is postulated to involve absorption of laser energy by a fraction of the analyte molecules that act as a sacrificial matrix or by residual water in the sample.
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Affiliation(s)
- Remilekun O. Lawal
- Department of Chemistry, Louisiana State University, Baton Rouge, Louisiana. 70803, USA
| | - Fabrizio Donnarumma
- Department of Chemistry, Louisiana State University, Baton Rouge, Louisiana. 70803, USA
| | - Kermit K. Murray
- Department of Chemistry, Louisiana State University, Baton Rouge, Louisiana. 70803, USA
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3
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Xiong R, Zhang Z, Chai W, Chrisey DB, Huang Y. Study of gelatin as an effective energy absorbing layer for laser bioprinting. Biofabrication 2017; 9:024103. [PMID: 28597844 DOI: 10.1088/1758-5090/aa74f2] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Laser-induced forward transfer printing, also commonly known as laser printing, has been widely implemented for three-dimensional bioprinting due to its unique orifice-free nature during printing. However, the printing quality has the potential to be further improved for various laser bioprinting applications. The objectives of this study are to investigate the feasibility of using gelatin as an energy absorbing layer (EAL) material for laser bioprinting and its effects on the quality of printed constructs, bioink printability, and post-printing cell viability and process-induced DNA damage. The gelatin EAL is applied between the quartz support and the coating of build material, which is to be printed. Printing quality can be improved by EAL-assisted laser printing when using various alginate solutions (1%, 2%, and 4%) and cell-laden bioinks (2% alginate and 5 × 106 cells ml-1 in cell culture medium). The required laser fluence is also reduced due to a higher absorption coefficient of gelatin gel, in particular when to achieve the best printing type/quality. The post-printing cell viability is improved by ∼10% and DNA double-strand breaks are reduced by ∼50%. For all the build materials investigated, the gelatin EAL helps reduce the droplet size and average jet velocity.
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Affiliation(s)
- Ruitong Xiong
- Department of Mechanical and Aerospace Engineering, University of Florida, Gainesville, FL 32611, United States of America
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Ahmed EM, Barrera FJ, Early EA, Denton ML, Clark CD, Sardar DK. Maxwell's equations-based dynamic laser-tissue interaction model. Comput Biol Med 2013; 43:2278-86. [PMID: 24290944 DOI: 10.1016/j.compbiomed.2013.09.005] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2013] [Revised: 09/05/2013] [Accepted: 09/07/2013] [Indexed: 11/29/2022]
Abstract
Since its invention in the early 1960s, the laser has been used as a tool for surgical, therapeutic, and diagnostic purposes. To achieve maximum effectiveness with the greatest margin of safety it is important to understand the mechanisms of light propagation through tissue and how that light affects living cells. Lasers with novel output characteristics for medical and military applications are too often implemented prior to proper evaluation with respect to tissue optical properties and human safety. Therefore, advances in computational models that describe light propagation and the cellular responses to laser exposure, without the use of animal models, are of considerable interest. Here, a physics-based laser-tissue interaction model was developed to predict the dynamic changes in the spatial and temporal temperature rise during laser exposure to biological tissues. Unlike conventional models, the new approach is grounded on the rigorous electromagnetic theory that accounts for wave interference, polarization, and nonlinearity in propagation using a Maxwell's equations-based technique.
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Affiliation(s)
- Elharith M Ahmed
- Department of Physics and Astronomy, University of Texas at San Antonio, One UTSA Circle, San Antonio, TX 78249, USA; TASC Inc., 4141 Petroleum Road, Ft. Sam Houston, TX 78234-2644, USA
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5
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Processing and immobilization of chondroitin-4-sulphate by UV laser radiation. Colloids Surf B Biointerfaces 2013; 104:169-73. [DOI: 10.1016/j.colsurfb.2012.11.044] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2012] [Revised: 11/21/2012] [Accepted: 11/27/2012] [Indexed: 11/19/2022]
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6
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Stava E, Yu M, Shin HC, Shin H, Kreft DJ, Blick RH. Rapid fabrication and piezoelectric tuning of micro- and nanopores in single crystal quartz. LAB ON A CHIP 2013; 13:156-160. [PMID: 23142827 DOI: 10.1039/c2lc40925a] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
We outline the fabrication of piezoelectric through-pores in crystalline quartz using a rapid micromachining process, and demonstrate piezoelectric deformation of the pore. The single-step fabrication technique combines ultraviolet (UV) laser irradiation with a thin layer of absorbing liquid in contact with the UV-transparent quartz chip. The effects of different liquid media are shown. We demonstrate that small exit pores, with diameters nearing the 193 nm laser wavelength and with a smooth periphery, can be achieved in 350 μm thick quartz wafers. Special crater features centring on the exit pores are also fabricated, and the depth of these craters are tuned. Moreover, by applying a voltage bias across the thickness of this piezoelectric wafer, we controllably contract and expand the pore diameter. We also provide a sample application of this device by piezoelectrically actuating alamethicin ion channels suspended over the deformable pore.
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Affiliation(s)
- Eric Stava
- Department of Electrical and Computer Engineering, University of Wisconsin-Madison, 1415 Engineering Drive, Madison, WI 53706, USA.
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7
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Wolf U, Wolf M, Heusser P, Thurneysen A, Baumgartner S. Homeopathic Preparations of Quartz, Sulfur and Copper Sulfate Assessed by UV-Spectroscopy. EVIDENCE-BASED COMPLEMENTARY AND ALTERNATIVE MEDICINE 2011; 2011:692798. [PMID: 19474239 PMCID: PMC3137246 DOI: 10.1093/ecam/nep036] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/26/2008] [Accepted: 04/02/2009] [Indexed: 11/29/2022]
Abstract
Homeopathic preparations are used in homeopathy and anthroposophic medicine. Although there is evidence of effectiveness in several clinical studies, including double-blinded randomized controlled trials, their nature and mode of action could not be explained with current scientific approaches yet. Several physical methods have already been applied to investigate homeopathic preparations but it is yet unclear which methods are best suited to identify characteristic physicochemical properties of homeopathic preparations. The aim of this study was to investigate homeopathic preparations with UV-spectroscopy. In a blinded, randomized, controlled experiment homeopathic preparations of copper sulfate (CuSO4; 11c–30c), quartz (SiO2; 10c–30c, i.e., centesimal dilution steps) and sulfur (S; 11×–30×, i.e., decimal dilution steps) and controls (one-time succussed diluent) were investigated using UV-spectroscopy and tested for contamination by inductively coupled plasma mass spectrometry (ICP-MS). The UV transmission for homeopathic preparations of CuSO4 preparations was significantly lower than in controls. The transmission seemed to be also lower for both SiO2 and S, but not significant. The mean effect size (95% confidence interval) was similar for the homeopathic preparations: CuSO4 (pooled data) 0.0544% (0.0260–0.0827%), SiO2 0.0323% (–0.0064% to 0.0710%) and S 0.0281% (–0.0520% to 0.1082%). UV transmission values of homeopathic preparations had a significantly higher variability compared to controls. In none of the samples the concentration of any element analyzed by ICP-MS exceeded 100 ppb. Lower transmission of UV light may indicate that homeopathic preparations are less structured or more dynamic than their succussed pure solvent.
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Affiliation(s)
- Ursula Wolf
- Institute of Complementary Medicine KIKOM, University of Bern, 3010 Bern, Switzerland
- National High Magnetic Field Laboratory (NHMFL), Florida State University, Tallahassee, FL 32310, USA
- *Ursula Wolf:
| | - Martin Wolf
- Institute of Complementary Medicine KIKOM, University of Bern, 3010 Bern, Switzerland
- National High Magnetic Field Laboratory (NHMFL), Florida State University, Tallahassee, FL 32310, USA
| | - Peter Heusser
- Institute of Complementary Medicine KIKOM, University of Bern, 3010 Bern, Switzerland
| | - André Thurneysen
- Institute of Complementary Medicine KIKOM, University of Bern, 3010 Bern, Switzerland
| | - Stephan Baumgartner
- Institute of Complementary Medicine KIKOM, University of Bern, 3010 Bern, Switzerland
- National High Magnetic Field Laboratory (NHMFL), Florida State University, Tallahassee, FL 32310, USA
- Institute Hiscia, 4144 Arlesheim, Switzerland
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Sviridov AP, Kondyurin AV. Optical characteristics of cartilage at a wavelength of 1560 nm and their dynamic behavior under laser heating conditions. JOURNAL OF BIOMEDICAL OPTICS 2010; 15:055003. [PMID: 21054085 DOI: 10.1117/1.3484749] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
A double-integrating-sphere system was used to measure the diffuse transmittance, diffuse reflectance, and collimated transmittance of cartilage and polyacrylamide hydrogel samples as a function of temperature under 1560-nm laser heating conditions. The dynamic behavior of the absorption and scattering coefficients and scattering anisotropy of the biomaterials was calculated by the inverse Monte Carlo method. The absorption coefficient of the cartilage and hydrogel samples proved to be linear in temperature. Raising the temperature of the cartilage samples to 80°C caused their absorption coefficient to decrease by some 25%. The temperature-induced change of the absorption spectrum of the interstitial water was found to be responsible for the clarification of the cartilage tissue observed to occur under 1560-nm laser heating conditions. The temperature field produced in the tissue by the laser energy deposited therein was calculated using a bioheat transfer equation with temperature-dependent parameters. The calculation results demonstrated that the temperature-induced changes of the optical parameters of biological tissues should be taken into account to make their 1560-nm laser treatment effective and safe.
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Affiliation(s)
- Alexander P Sviridov
- Russian Academy of Sciences, Institute on Laser and Information Technologies, Troitsk, Moscow Region, 142190, Russia.
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Lin Y, Huang G, Huang Y, Tzeng TRJ, Chrisey DB. Process-Induced Cell Injury in Laser Direct Writing of Human Colon Cancer Cells. Tissue Eng Part C Methods 2010:110525193859077. [PMID: 20151815 DOI: 10.1089/ten.tec.2009.0606] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Matrix-assisted pulsed-laser evaporation direct-write has emerged as a promising technique for biological construct fabrication. The posttransfer cell viability in matrix-assisted pulsed-laser evaporation direct-write depends on various operating conditions such as the applied laser fluence. To date, the effects of operating conditions such as laser fluence, direct-writing height, and cell density on the posttransfer cell viability have not been well elucidated. This study investigates the effects of operating conditions on the posttransfer cell viability in laser direct writing of human colon cancer HT-29 cells. It has been observed that (1) the HT-29 cell viability decreases from 95% to 78% as the laser fluence increases from 258 to 1482 mJ/cm(2), and the posttransfer cell proliferation capacity does not vary significantly as the laser fluence changes; (2) the direct-writing height does not have noticeable effect on the posttransfer cell viability under low laser fluences (258 and 869 mJ/cm(2)). However, a larger height (such as 29.3 mm) led to an almost 8% viability improvement compared with that of 16.6 mm under a high laser fluence (1482 mJ/cm(2)); and (3) the posttransfer cell viability is not dependent on the cell density for a range from 1 × 10(6) to 1 × 10(7) cells/mL.
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Affiliation(s)
- Yafu Lin
- 1 Department of Mechanical Engineering, Clemson University , Clemson, South Carolina
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10
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Mrochen M, Wuellner C, Rose K, Donitzky C. Experimental setup to determine the pulse energies and radiant exposures for excimer lasers with repetition rates ranging from 100 to 1050 Hz. J Cataract Refract Surg 2009; 35:1806-14. [DOI: 10.1016/j.jcrs.2009.05.021] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2008] [Revised: 05/25/2009] [Accepted: 05/27/2009] [Indexed: 10/20/2022]
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11
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Mrochen M, Schelling U, Wuellner C, Donitzky C. Influence of spatial and temporal spot distribution on the ocular surface quality and maximum ablation depth after photoablation with a 1050 Hz excimer laser system. J Cataract Refract Surg 2009; 35:363-73. [DOI: 10.1016/j.jcrs.2008.10.053] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2008] [Revised: 10/08/2008] [Accepted: 10/28/2008] [Indexed: 11/26/2022]
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Higashi N, Ikehata A, Ozaki Y. An attenuated total reflectance far-UV spectrometer. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2007; 78:103107. [PMID: 17979406 DOI: 10.1063/1.2796928] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/15/2023]
Abstract
An ultraviolet spectrometer based on attenuated total reflection (ATR) has been developed and tested for liquid water (light and heavy water) in the wavelength range from 140 to 300 nm, which includes the far ultraviolet (FUV) region. One of the principal limitations of FUV transmission spectra is the strong absorption of the solvent itself. High absorptivity of the n --> sigma(*) transition in water molecule has thus far prevented meaningful spectral measurements of aqueous solutions in the wavelength region under 170 nm. Our technique uses the evanescent wave created through total reflection when light is passed through an internal reflection element (IRE) in contact with the sample. Since the evanescent field is used as an optical path length, the method allows spectral measurements favorably comparable with that of transmittance method with a shorter path length than the wavelength of FUV light. In this study, we have designed an original miniature IRE probe made of sapphire that allows detection of the whole n --> sigma(*) transition absorption band of water down to 140 nm. The obtained ATR-FUV spectra closely match calculations based on the Fresnel formula. It is also confirmed that this spectrometer is equally effective for spectral measurements of nonaqueous solvents with significant absorptivities in the FUV region.
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Affiliation(s)
- Noboru Higashi
- KURABO Industries Ltd., 14-5 Shimokida-cho, Neyagawa 572-0823, Japan
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13
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Fisher BT, Hahn DW. Measurement of small-signal absorption coefficient and absorption cross section of collagen for 193-nm excimer laser light and the role of collagen in tissue ablation. APPLIED OPTICS 2004; 43:5443-5451. [PMID: 15508600 DOI: 10.1364/ao.43.005443] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
A 193-nm ArF excimer laser transmission was measured at subablative fluence through varying strength solutions of dissolved collagen, yielding an absorption cross section of 1.14 x 10(-17) cm2 for the peptide bond, which accounts for 96% of the total collagen attenuation that is based on additional transmission measurements through solutions of isolated constituent amino acids. The measured absorption cross sections, in combination with typical corneal tissue composition, yield a predicted corneal tissue absorption coefficient of 16,000 cm(-1). In addition, dry collagen films were prepared and ablation-rate data were recorded as a function of laser fluence. Ablation rates were modeled by use of a Beer-Lambert blow-off model, incorporating a measured ablation threshold and an absorption coefficient that are based on the measured collagen absorption cross section and the film bond density. The measured ablation rates and those predicted by the model were in very good agreement. The experiments suggest that collagen-based absorption coefficients are consistent with predicted corneal tissue ablation rates and previously observed dynamic changes in tissue properties under ablative conditions.
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Affiliation(s)
- Brian T Fisher
- Department of Mechanical and Aerospace Engineering, University of Florida, Gainesville, Florida, USA
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Affiliation(s)
- Alfred Vogel
- Medical Laser Center Lübeck, Peter-Monnik-Weg 4, D-23562 Lübeck, Germany.
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15
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Georgiou S, Koubenakis A. Laser-induced material ejection from model molecular solids and liquids: mechanisms, implications, and applications. Chem Rev 2003; 103:349-94. [PMID: 12580635 DOI: 10.1021/cr010429o] [Citation(s) in RCA: 107] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Affiliation(s)
- Savas Georgiou
- Institute of Electronic Structure and Laser, Foundation for Research and Technology-Hellas, PO Box 1527, 71110 Heraklion, Crete, Greece.
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Abstract
BACKGROUND AND OBJECTIVE The pulsed CO2 laser has received attention because of its successful application to dermatologic surgery and burn debridement surgery. Despite impressive results, tissue removal using pulsed CO2 laser irradiation has not been optimized. We examined the ablation processes by performing mass removal and thermal injury experiments at wavelengths where tissue water is the primary absorber (10.6 microm), and where water and collagen have comparable absorption (9.5 microm). STUDY DESIGN/MATERIALS AND METHODS Samples of porcine reticular dermis were irradiated with 180-ns laser pulses at either wavelength. Tissue removal was measured using a digital balance. Thermal injury was assessed using a microscope with a calibrated reticle after hematoxylin and eosin staining. RESULTS Tissue removal using 10.6-microm radiation resulted in a heat of ablation of 3,740 J/g, an ablation threshold of 1.15 J/cm2, and a zone of thermal injury of 53 microm. By contrast, tissue removal using 9.5-microm radiation resulted in a heat of ablation of 3,330 J/g, an ablation threshold of 1.47 J/cm2, and a zone of thermal injury of 34 microm. The differences in ablation threshold and thermal injury were statistically significant. CONCLUSION Pulsed CO2 laser irradiation at 9.5 microm removes tissue more efficiently and with a smaller zone of thermal injury than at 10.6 microm.
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Affiliation(s)
- B P Payne
- Wellman Laboratories of Photomedicine, Harvard Medical School, Massachusetts General Hospital, Boston 02114, USA.
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Mrochen M, Semshichen V, Funk RH, Seiler T. Limitations of Erbium:YAG Laser Photorefractive Keratectomy. J Refract Surg 2000; 16:51-9. [PMID: 10693619 DOI: 10.3928/1081-597x-20000101-07] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
PURPOSE The erbium:YAG laser (lambda = 2.94 microm) has been considered promising as an alternative to the ArF excimer laser in photorefractive keratectomy (PRK). However, corneal application of this mid-infrared solid state laser is still plagued with various disadvantages compared to that of the ArF excimer laser (lambda = 193 nm). We discuss the limitations of PRK with the erbium:YAG laser. METHODS Measurements of ablation threshold, ablation efficiency, and thermal damage were done to compare the process of erbium:YAG laser photoevaporization to the ArF excimer laser. PRK procedures were performed on fresh enucleated pig corneas to investigate the morphology and surface roughness of the cornea after scanning-spot and fundamental mode photoablation. Surface roughness was measured by using a tactile surface reprofiling system. RESULTS The ablation threshold and the ablation efficiencies for the erbium:YAG laser are significantly higher compared to the ArF excimer laser. Collateral thermal damage decreases with a reduction of laser pulse duration to a minimum of approximately 5 microm. Scanning electron microscopy and surface roughness measurements of the corneal surface after erbium:YAG laser treatment demonstrated higher surface roughness compared to ArF excimer laser treatments. CONCLUSIONS The erbium:YAG laser is not at present an alternative to the ArF excimer laser for photorefractive keratectomy.
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Affiliation(s)
- M Mrochen
- University of Dresden, Department of Ophthalmology, Germany.
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18
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Yablon AD, Nishioka NS, Mikić BB, Venugopalan V. Measurement of tissue absorption coefficients by use of interferometric photothermal spectroscopy. APPLIED OPTICS 1999; 38:1259-72. [PMID: 18305741 DOI: 10.1364/ao.38.001259] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
We describe a spectroscopic technique called interferometric photothermal spectroscopy (IPTS) that can measure the absorption coefficient of pulsed laser radiation in nonscattering tissue samples. The technique is suitable for measuring effective absorption coefficients from 10(3) to 10(5) cm(-1). IPTS is particularly attractive because it requires minimal disturbance of the sample. These features indicate potential use for in vivo measurements of tissue absorption coefficients. To validate the technique, the absorption coefficient of pulsed Q-switched Er:YSGG (2.79-microm) radiation in pure water was measured to be 5200 (+/-500) cm(-1) when IPTS was used, in agreement with other published values. IPTS was also used to measure the absorption coefficient of pulsed ArF excimer laser radiation (193 nm) in bovine corneal stroma (in vitro), giving a value of 1.9 (+/-0.4) x 10(4) cm(-1).
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Affiliation(s)
- A D Yablon
- Wellman Laboratories of Photomedicine, Massachusetts General Hospital, Boston, Massachusetts 02114, USA
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Oshika T, Klyce SD, Smolek MK, McDonald MB. Corneal hydration and central islands after excimer laser photorefractive keratectomy. J Cataract Refract Surg 1998; 24:1575-80. [PMID: 9850893 DOI: 10.1016/s0886-3350(98)80345-3] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
PURPOSE To determine whether uneven corneal surface hydration during excimer laser photorefractive keratectomy (PRK) is related to postoperative occurrence of central islands. SETTING LSU Eye Center, New Orleans, Louisiana, USA. METHODS A retrospective study reviewed intraoperative videotapes and postoperative videokeratography of 49 eyes of 49 patients who had excimer laser PRK for myopia. The uniformity of corneal hydration within the photoablation zone, particularly the frosty appearance of the ablated zone, was characterized. The presence or absence of a topographic central island (steepening of at least 3.0 diopters and 1.5 mm in diameter) was determined from the 1 month postoperative videokeratographs. RESULTS Twelve eyes (24.5%) developed central islands postoperatively. A statistically significant association was observed between the uneven surface hydration (central accumulation of fluid) within the ablation zone intraoperatively and the formation of central islands postoperatively (P < .001, Kruskal-Wallis test; Kendall tau rank correlation = 0.534; P < .001). CONCLUSION Nonuniform fluid distribution during photoablation was a risk factor for central island formation after PRK. Intraoperatively, the presence of excess fluid in the central cornea appeared as a shiny area. This mirror-like surface layer may reduce the rate of central ablation by reflecting and absorbing a significant amount of the incident excimer laser light.
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Affiliation(s)
- T Oshika
- Department of Ophthalmology, University of Tokyo School of Medicine, Tokyo, Japan
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