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At least 703 records · Page 39Linked to original sources
PubMed1984

Histopathologic verification of position of laser burns in argon laser trabeculoplasty.

Surgical trabeculectomy was performed on 10 eyes of 10 patients following failure of argon laser trabeculoplasty. All specimens were examined by scanning electron microscopy to determine anatomic location of laser damage. Correlation with clinical data revealed accurate placement of laser burns in 11 out of 13 treatment sessions. The degree of laser injury varied with energy delivered and pigmentation of the posterior trabecular meshwork. Complications such as corneal endothelial, oblique, and confluent burns were present in 50% of cases studied.

Argon↗
PubMed1993

[Experimental laser sclerostomy ab externo with erbium:YAG laser].

A fistula from the anterior chamber of the eye into the subconjunctival space can be created by external laser application (laser sclerostomy). A pulsed (200 microseconds) Erbium-YAG laser was used because of the high scleral absorption. The laser energy was applied via a special fiber, which was inserted into a special application cannula to guide it into the subconjunctival space. A total of 24 rabbit eyes were treated and examined histologically after various postoperative periods. In all cases a functioning fistula and a marked reduction of the IOP (mean value 13 mmHg to 2 mmHg) were detected. On average, 60 mJ was required. The zone of thermal damage was limited to 40 microns. Cornea and lens showed no evidence of damage after 1 day or after 4 weeks. In the rabbit model, the fistulas were closed within 2 weeks, and long-term persistence of the fistula must therefore be verified in a clinical study. The method presented is minimally invasive, requires only a short operation time, causes minimal trauma to the conjunctiva, and may become an alternative to traditional fistulization operations.

Animals↗
PubMed1996

Morphological and biomorphometrical observations on laser thermal keratoplasty. Histological and biomorphometrical examination of the relationship between refractive change and the volume following Cr:Tm:Ho:YAG laser treatment.

Laser thermal keratoplasty (LTK) is currently under clinical trial for the correction of hyperopia and hyperopic astigmatism by means of collagen coagulation in the peripheral cornea. The purpose of our study was to optimize the ratio between the volume of damaged corneal stroma and the refractive effect so as to minimize potential side effects such as endothelial damage or induction of glare phenomena. We therefore performed histological and morphometrical examinations of enucleated pig eyes to determine the relationship between the coagulated stromal volume and the refractive change after LTK using a pulsed Cr:Tm:Ho:YAG laser (wavelength 2.12 microns) on enucleated pig eyes. The refractive change was documented with a Littman ophthalmometer. Morphometrical analysis was performed using polarized light microscopy of sirius red-stained specimens. This special stain separated the thermally changed stroma into a dark nonbirefringent center and a birefringent peripheral zone. The volume of both zones was positively correlated with the refractive change induced. The volume was in turn influenced by the choice of laser parameters. From the ratio of the volume to the refractive change it was found that pulse energies above 30 mJ let to an enlargement of the coagulation volume without increasing the refractive change effectively. The use of high pulse energies did not improve the effect of LTK but only increased the risk of unwanted side effects. However, an increase in the laser repetition rate at a constant pulse number per spot led to refractive changes with minimal coagulation volume. The highest relative refractive change was achieved with a dark central zone and a birefringent zone, each having a volume of about 50-80 x 10(-3) mm3.

Animals↗
PubMed1996

[The potentials of laser and electromagnetic-laser therapy in the treatment of patients with arteriosclerosis obliterans of the vessels of the lower extremities].

A comparative analysis of the laser and electromagnetic laser therapy was performed in the complex treatment of patients with obliterating atherosclerosis of the lower extremity vessels. Laser treatment exerts a therapeutic effect related with its influence upon microcirculation. The effectiveness of complex treatment becomes higher when using a combination of laser therapy with the impulse electromagnetic therapy of complex modulation at the expense of improvement of the regional blood circulation in all links of the vasculature.

Arteriosclerosis Obliterans↗
PubMed1997

The Q-switched neodymium:YAG laser and tattoos: a microscopic analysis of laser-tattoo interactions.

The Nd:YAG laser effectively removes or lightens amateur and professional tattoos. The biomechanics of the removal of tattoo particles at the cellular level are incompletely understood. We examined biopsies obtained from 35 amateur and professional tattoos (including coloured tattoos), treated on three or more occasions with the Nd:YAG laser. Biopsies taken immediately after laser treatment showed vacuolation with complete clearance of tattoo particles in the most superficial layers of the dermis, as assessed by light and electron microscopy. We propose that the 'disappearance' of the tattoo particle arises from the formation of atomic species and gaseous products, which are rapidly dissolved in the extracellular fluid. Residual fragmented particles that are commonly found in the mid- and lower dermis are rephagocytosed. The interaction between the Nd:YAG laser and black tattoo particles at 1064 nm, and red tattoo particles at 532 nm, appears to be specific, as there was little evidence of thermal damage to adjacent cells or stromal collagen.

Humans↗
PubMed1998

Laser stapedotomy minus prosthesis (laser STAMP): a minimally invasive procedure.

OBJECTIVE: To determine whether hearing can be restored using a laser without a prosthesis in patients with minimal otosclerosis. STUDY DESIGN: Retrospective case review of 12 patients with minimal otosclerosis who underwent a laser stapedotomy without prosthesis (laser STAMP) procedure. SETTING: An otology/neurotology tertiary referral center. PATIENTS: Patients were chosen for the procedure if there was a blue footplate with minimal otosclerosis confined to the fissula antefenestram. INTERVENTIONS: Using a hand-held probe (CeramOptic), and the HGM argon laser, the anterior crus of the stapes was vaporized. Next, a linear stapedotomy was made across the anterior one third of the footplate. If otosclerosis is confined to the fissula antefenestram, the stapes becomes completely mobile. The stapedotomy opening is sealed with an adipose tissue graft from the ear lobe. MAIN OUTCOME MEASURES: Pure-tone audiometry with appropriate masking and auditory discrimination testing were performed before surgery, 6 weeks after surgery, and 1 year after surgery. RESULTS: The average air-bone gap was closed to a mean (SD) of 2.6 dB (3.3 dB). The average improvement in air-bone gap was 17.4 dB (7.6 dB). The discrimination scores remained unchanged. Audiometric testing of five cases with 1 year follow-up demonstrates that excellent hearing results are maintained. CONCLUSIONS: In selected cases of minimal otosclerosis confined to the fissula antefenestram, normal mobility of the ossicular chain can be obtained without a prosthesis by vaporizing the anterior crus and making a linear stapedotomy across the anterior one third of the footplate. The advantages of the procedure are that the stapedius tendon and most of the normal stapes remain intact, eliminating hyperacusis. The procedure is less invasive so it reduces inner ear trauma, possible prosthesis problems are avoided, and postoperative barotrauma risk is minimized. Minimal surgery is done for minimal disease. If the stapes refixes at some time in the future, a conventional stapedotomy can still be performed.

Adult↗
PubMed1998

Reproducibility of the laser flare meter and laser cell counter in assessing anterior chamber inflammation following cataract surgery.

BACKGROUND AND OBJECTIVES: To determine the interobserver and intraobserver reproducibility of the laser flare meter and laser cell counter in assessing anterior chamber inflammation following cataract surgery. PATIENTS AND METHODS: Thirty-nine eyes with varied degrees of inflammation and 9 normal eyes were included in the study. Anterior chamber flare and cells were evaluated with the slit lamp and graded on a scale of 0 to 4+. The flare and cells were then measured three times each using the flare meter and cell counter by two different, experienced observers. The intraobserver reproducibilities were computed to evaluate repeatability of the instruments operated by the same observer. The first measurement taken by each observer was used to assess reproducibility between the two observers. RESULTS: The intraobserver reproducibility for overall flare was 0.995 for both observers. The intraobserver reproducibility for overall cells was 0.996 for observer 1 and 0.991 for observer 2. The overall interobserver reproducibility was 0.994 for flare and 0.988 for cells. The correlation between measurements and slit-lamp ratings was 0.78 for flare and 0.56 for cells. CONCLUSIONS: The intraobserver and interobserver reproducibilities were excellent, with good correlation to slit-lamp measurements. Reproducible results can be obtained using the laser flare meter and the laser cell counter. It is not known whether these results are applicable to other inflammatory processes with higher grades of flare and cells and with different protein and cell types.

Anterior Chamber↗
PubMed1998

The Laser Institute of America's laser hazard evaluator.

The Laser Institute of America recently developed a software program, the Laser Hazard Evaluator, to help analyze the risks involved in using most types of lasers. In this article, we review the uses and characteristics of the Laser Hazard Evaluator and present ECRI's judgment of its merits.

Equipment Safety↗
PubMed1991

Progressive enlargement of laser scars following grid laser photocoagulation for diffuse diabetic macular edema.

Laser photocoagulation in a grid pattern is effective in many eyes in resolving diffuse diabetic macular edema and stabilizing vision. We retrospectively studied 203 eyes of 203 patients, all of whom had diabetic macular edema treated with grid laser photocoagulation. During the follow-up period, 11 of these 203 eyes developed enlargement of the laser scars that progressed into the central fovea. Each of the 11 eyes experienced loss of vision, and in five, the visual loss was significant. Five of these eyes also developed a retinal pigment hyperplastic scar. After the laser treatment, but before the scars enlarged, the visual acuity of these eyes was unchanged from that before treatment. But after the atrophic scars enlarged into the central fovea, visual acuity in one eye decreased from 20/40 to 20/100, and the other 10 eyes had visual acuities of 20/200 or worse.

Aged↗
PubMed1998

Methanol Laser Line Assignments: Evidence of Four-Level Laser Systems

The "Ritz" computer program, developed for facilitating the assignment of molecular Fourier transform absorption spectra and described in a previous work, determines the energy level values involved in the assigned transitions by the Rydberg-Ritz combination principle. Combining the data obtained from the analyses of high-resolution infrared (IR) and far-infrared (FIR) spectra, it is possible to predict possible FIR laser emissions of molecules. In the present work we have applied this method to the common isotopomer methanol, 12CH3 16OH, and obtained 14 proposed assignments for previously unassigned FIR laser lines. We also predict 15 possible new FIR laser emissions. For the first time, an assignment involving a four-level laser system with collisional population transfer to a slightly higher energy level is reported. Copyright 1998 Academic Press.

Journal Article↗
PubMed1998

Quantitative Intracavity Laser Spectroscopy Measurements with a Ti:sapphire Laser: Absorption Intensities for Water Vapor Lines in the 790-800 nm Region.

The intracavity laser spectroscopy (ILS) technique has been shown to be a very sensitive method for observing absorption spectra. By considering quantitative results (line-strengths and pressure broadening coefficients) obtained using the ILS method with a dye laser, the technique has been shown to provide quantitative information that is in excellent agreement with the values afforded by use of more traditional methods for acquiring absorption spectra. A similar investigation has been conducted for an ILS system based on a Ti:sapphire laser. Presented here are quantitative results for water vapor transitions occurring around 795 nm. Line intensities are determined as a function of water vapor pressure and effective path length (i.e., generation time). The line-strengths are compared with values determined by R. A. Toth [J. Mol. Spectrosc. 166, 176-183 (1994)] who used a multipass cell and the Fourier transform spectrometer at the Kitt Peak National Observatory. The good agreement between the results demonstrates that quantitatively accurate data can be obtained using the ILS technique with a Ti:sapphire laser. Copyright 1998 Academic Press.

Journal Article↗
PubMed2001

Indirect laser-induced fluorescence detection for capillary electrophoresis using a violet diode laser.

The violet (415 nm) diode laser is used for indirect laser-induced fluorescence detection in capillary electrophoretic separations of inorganic anions and chemical warfare agent degradation products. Inorganic anions were detected using 8-hydroxypyrene-1,3,6-trisulfonic acid as the indirect probe and achieved submicromolar (40-80 ppb) detection limits in a 2-min separation. The chemical warfare agent degradation products methylphosphonic acid, ethyl methylphosphonate, isopropyl methylphosphonate, and pinacolyl methylphosphonate were detected using the porphyrin tetrakis(4-sulfophenyl)porphine as the indirect probe and achieved detection limits of 0.1 microM (9 ppb), which are 1 order of magnitude better than that achieved using indirect UV detection. Baseline stability achieved with the violet diode laser was excellent, with dynamic reserve (DR) values of > 1000, which are 15 times better than that achieved using an unstabilized HeCd laser.

Journal Article↗
PubMed2006

Photodissociation of naphthalene dimer radical cation during the two-color two-laser flash photolysis and pulse radiolysis-laser flash photolysis.

Photodissociation of naphthalene (Np) dimer radical cation (Np2*+) to give naphthalene radical cation (Np*+) and Np and the subsequent regeneration of Np2*+ by the dimerization of Np*+ and Np were directly observed during the two-color two-laser flash photolysis in solution at room temperature. When Np2*+ was excited at the charge-resonance (CR) band with the 1064-nm laser, the bleaching and recovery of the transient absorption at 570 and 1000 nm, assigned to the local excitation (LE) and CR bands of Np2*+, respectively, were observed together with the growth and decay of the transient absorption at 685 nm, assigned to Np*+. The dissociation of Np2*+ proceeds via a one-photon process within the 5-ns laser flash to give Np*+ and Np in the quantum yield of 3.2 x 10(-3) and in the chemical yield of 100%. The recovery time profiles of Np2*+ at 570 and 1000 nm were equivalent to the decay time profile of Np*+ at 685 nm, suggesting that the dimerization of Np*+ and Np occurs to regenerate Np2*+ in 100% yield. Similar experimental results of the photodissociation and regeneration of Np2*+ were observed during the pulse radiolysis-laser flash photolysis of Np in 1,2-dichloroethane. The photodissociation mechanism can be explained based on the crossing between two potential surfaces of the excited-state Np2*+ and ground-state Np*+.

Journal Article↗
PubMed2005

Comparative study of aminolevulic acid photodynamic therapy plus pulsed dye laser versus pulsed dye laser alone in treatment of viral warts.

OBJECTIVE AND BACKGROUND: A number of scientific publications describe the removal of viral warts using photoselective laser destruction with pulsed dye laser (PDL) or photodynamic therapy (PDT). Although both methods represent an enormous improvement in therapy, the results are not sufficiently consistent to consider these methods as the "gold standard" for therapy. METHODS: With a view to further improvement we combined a photoselective dye laser (595 nm, 20 J.cm(-2)) with photodynamic therapy using aminolevulic acid. The results of this method were compared against traditional laser photodestruction (of identical physical parameters) and against traditional photodynamic therapy (of similar parameters). RESULTS: After combined therapy (PDT + PDL) of 86 warts in 24 patients, 100% were cured, with an average of 1.96 therapeutic sessions. Therapy with PDT alone failed in 3 of 76 warts even after 5 sessions (96%), with an average of 2.54 therapeutic sessions. Therapy with PDL alone failed in 21 of 112 warts even after 5 sessions, with an average of 3.34 therapeutic sessions. CONCLUSIONS: All three therapeutic methods are able to cure infectious warts with high probability (>80%). However, a combination of PDT and PDL is the most effective and the most favored therapy. If other investigators also confirm results near or equal to 100% success, this therapy could become a treatment of choice for this indication.

Aminolevulinic Acid↗
PubMed1999

Soft-x-ray laser interferometry of a pinch discharge using a tabletop laser.

We have used a tabletop soft-x-ray laser and a wave-front division interferometer to probe the plasma of a pinch discharge. A very compact capillary discharge-pumped Ne-like Ar laser emitting at 46.9 nm was combined with a wave division interferometer based on Lloyd's mirror and Sc-Si multilayer-coated optics to map the electron density in the cathode region of the discharge. This demonstration of the use of tabletop soft-x-ray laser in plasma interferometry could lead to the widespread use of these lasers in the diagnostics of dense plasmas.

Journal Article↗
PubMed2001

Hot electrons in the interaction of femtosecond laser pulses with foil targets at a moderate laser intensity.

Characteristics of hot electrons produced in the interaction of femtosecond laser pulses with foil targets were investigated at a moderate laser intensity. Both outgoing and ingoing hot electrons from the femtosecond laser plasma were studied. A collimated jet of outgoing hot electrons was observed in the target normal direction. An ingoing energetic hot-electron beam was found in the laser propagation direction, while the low-energy ingoing electrons spread into wider cone angle due to the collisional effects in the plasma and target material. These observations were supported by three-dimensional Monte Carlo simulations. The hot-electron temperature obtained from electron spectra and absorption experiments implies that resonance absorption is partially responsible for the generation of hot electrons.

Journal Article↗
PubMed2001

Numerical study of laser wake field generated by two colliding laser beams.

The laser wake field generated by two colliding laser beams has been studied numerically. The wake field amplitude is enhanced by a counterpropagating long pulse laser, which has an appropriate frequency difference, and becomes an order of magnitude larger than that of the standard wake field. The field amplitude increases in proportion to the pumping laser intensities until it saturates under the wave breaking limit. The details of the enhanced wake field have been examined at the saturated state.

Journal Article↗
PubMed2006

Observation of strong correlation between quasimonoenergetic electron beam generation by laser wakefield and laser guiding inside a preplasma cavity.

We use a one-shot measurement technique to study effects of laser prepulses on the electron laser wakefield acceleration driven by relativistically intense laser pulses (lambda=790 nm, 11 TW, 37 fs) in dense helium gas jets. A quasimonoenergetic electron bunch with an energy peak approximately 11.5 MeV[DeltaE/E approximately 10% (FWHM)] and with a narrow-cone angle (0.04pi mm mrad) of ejection is detected at a plasma density of 8 x 10(19) cm(-3). A strong correlation between the generation of monoenergetic electrons and optical guiding of the pulse in a thin channel produced by picosecond laser prepulses is observed. This generation mechanism is well corroborated by two-dimensional particle-in-cell simulations.

Journal Article↗