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Krypton laser photocoagulation was performed in 15 eyes of 13 patients with angioid streaks associated with disciform lesions. Treatment was successful in seven eyes; in eight eyes subfoveolar recurrences developed, resulting in loss of central vision. Angioid streaks running through the macular area and a diffuse maculopathy stimulate recurrences of neovascular outgrowth at the posterior pole.
Choroidal neovascularization is considered to be the cause of exudate or subretinal hemorrhage formation in the evolution of different types of macular degeneration (exudative senile macular degeneration, idiopathic macular degeneration, presumed ocular histoplasmosis, angioid streaks, etc. The only curative treatment which has proved to be successful is the destruction of subretinal neovascularisation by photocoagulation. The effect of laser photocoagulation depends on the radiation wavelength emitted and the absorption spectrum of the target tissue. It is for this reason that the red krypton laser is recommended for the destruction of subretinal neovascularizations, its action being restricted to the choroid without inflicting damage on the nerve fiber layer.
Using a newly constructed three sector field mass spectrometer (resulting in a BE1E2 field configuration) we have measured the kinetic energy release distributions of neon, argon, and krypton cluster ions. In the present study we used the first two sectors, B and E1, constituting a high resolution mass spectrometer, to select the parent ions in terms of mass, charge, and energy, and studied the decay of those ions in the third field free region. Due to the improved mass resolution we were able to extend earlier studies carried out with a two sector field machine, where an upper size limit arose from the fact that several isotopomers contribute to a decaying parent ion beam when the cluster size exceeds a certain value. Furthermore we developed a new data analysis. It allows us to model also fragment ion peaks that are a superposition of different decay reactions and thus we can determine the average kinetic energy release for all decay reactions of a given cluster ion. In a further step we used these results to determine the binding energies of cluster ions Rg(n) (n> or =10) by applying finite heat bath theory. The smaller sizes have not been included in this analysis, because the validity of finite heat bath theory becomes questionable below n approximately 10. The present average kinetic energy releases and binding energies are compared with other experiments and various calculations.
Gibbs ensemble Monte Carlo simulations were used to test the ability of intermolecular pair potentials derived ab initio from quantum mechanical principles, enhanced by Axilrod-Teller triple-dipole interactions, to predict the vapor-liquid phase equilibria of pure neon, pure argon, and the binary mixtures neon-argon and argon-krypton. The interaction potentials for Ne-Ne, Ar-Ar, Kr-Kr, and Ne-Ar were taken from literature; for Ar-Kr a different potential has been developed. In all cases the quantum mechanical calculations had been carried out with the coupled-cluster approach [CCSD(T) level of theory] and with correlation consistent basis sets; furthermore an extrapolation scheme had been applied to obtain the basis set limit of the interaction energies. The ab initio pair potentials as well as the thermodynamic data based on them are found to be in excellent agreement with experimental data; the only exception is neon. It is shown, however, that in this case the deviations can be quantitatively explained by quantum effects. The interaction potentials that have been developed permit quantitative predictions of high-pressure phase equilibria of noble-gas mixtures.
We present the first prediction for the fragmentation dynamics following electron impact ionization of neutral krypton clusters from 2 to 11 atoms. Fragment proportions and parent ion lifetimes are deduced from a molecular dynamics with quantum transitions study in which the nuclei are treated classically and the transitions between electronic states quantum mechanically. The potential-energy surfaces are derived from a diatomics-in-molecules model to which induced dipole-induced dipole and spin-orbit interactions are added. The results show surprisingly fast and extensive fragmentation for clusters of such a heavy atom, although not as extensive as in the case of neon clusters studied previously [D. Bonhommeau et al., J. Chem. Phys. 123, 54316 (2005)]. The parent ion lifetimes range from 2.8 to 0.7 ps, and the most abundant fragment is Kr(2) (+) for all studied sizes, followed by Kr(+) for sizes smaller than 7 atoms and by Kr(3) (+) for larger sizes. Trimer and larger fragments are found to originate from the lower electronic states of parent ions. The comparison with preliminary results from experiments on size-selected neutral clusters conducted by Steinbach et al. (private communication) reveal a good agreement on the extensive character of the fragmentation. It is checked that the additional internal energy brought by the helium scattering technique used for size selection does not affect the fragment proportions. In addition, the existence of long-lived trajectories is revealed, and they are found to be more and more important for larger cluster sizes and to favor the stabilization of larger fragments. The implications of this work for microsecond-scale dynamics of ionized rare-gas clusters are discussed. In particular, given the extent of fragmentation of the parent clusters and the fast kinetics of the whole process, the small cluster ions that exhibit a monomer loss in the microsecond time window must originate from much larger neutral precursors. The decay rate of the II(12)(u) state of the ionic dimer Kr(2) (+) by spin-orbit coupling is found to be of the order of 3 ps, in contrast to the expected tens of microseconds, but only reasonably faster than the corresponding state of HeNe(+). Finally, the spin-orbit interaction strongly affects both the Kr(+)Kr(2) (+) ratio and some of the characteristic times of the dynamics, especially for smaller sizes, but not the overall dependence of the fragment proportions as a function of cluster size.
Time-resolved coherent anti-Stokes Raman-scattering (CARS) measurements are carried out to study the interaction between xenon atom and iodine molecule in a solid krypton matrix. Interference between the CARS polarizations of the "free" and complexed iodine molecules is observed, while the quantum beats of the complex are not detected due to low concentration. Vibrational analysis based on the polarization beats yields accurate molecular constants for the I2-Xe complex. The harmonic frequency of the I2-Xe complex is found to be redshifted by 0.90 cm-1 when compared to the free I2, whereas the anharmonicity is approximately the same. The dephasing rate of the complex is found to be somewhat higher than that of the free iodine molecule in solid Kr, showing that the complexation affects dephasing, although not dramatically. Molecular dynamics simulations are carried out to find the conformation of the complex, and wave packet simulations are used to reproduce the CARS signal to confirm the assignments of the observed beatings as quantum and polarization beats. The results show that the polarization beats are a useful tool for investigating weak interactions in condensed phase.
The Coulomb explosion of K-shell ionized krypton clusters with an average size N of 160 has been studied by electron-multiple-ion-coincidence measurements in which the time-of-flight (TOF) of ions was measured by using a position sensitive detector. The authors have sorted the TOF spectra by the number of coincidence ion signals, Ncoin, and found that singly charged fragment ions such as Kr+, Kr2+, and Kr3+ are dominant for Ncoin>or=2, and that multiply charged ions are detected mainly for Ncoin=1. The Ncoin dependence of the peak widths in the TOF spectra reveals that the average momentum of the Kr+ ions increases with Ncoin, while those of Kr2+ and Kr3+ decrease. These results have been more directly confirmed by the momentum imaging measurements. The authors propose that the heavier ions are produced in the central part of clusters where the Coulomb interactions from the surrounding ions are more effectively canceled out due to the higher symmetry.
Semianalytical and numerical calculations are performed to predict the structural and thermodynamic properties of low-density Kr fluid. Assuming that the interatomic forces can be modelled by a pairwise potential plus the three-body Axilrod-Teller potential, two different routes are explored. The first one is based on the hybridized mean spherical approximation integral equation of the theory of liquids and the second one uses large-scale molecular dynamics (MD). Algorithms for MD simulation are constructed on parallel machines to reduce the amount of computer time induced by the calculations of the three-body forces and the pair-correlation function. Our results obtained with the two methods mentioned above are in quite good agreement with the recent small-angle neutron-scattering experiments [Formisano et al., Phys. Rev. Lett. 79, 221 (1997); Benmore et al., J. Phys.: Condens. Matter 11, 3091 (1999)]. Moreover, the reliability of the asymptotic form of the integral equation is assessed for the specific case of dispersion forces including the three-body contributions, by an analysis at low wave vector and low density. It is seen that the effects of the Axilrod-Teller triple-dipole potential cannot be ignored to describe the structure and the thermodynamic properties of fluid krypton even at low density.
The Soret and the other transport coefficients, characterizing the heat and mass transport in binary mixtures, have been obtained by equilibrium and nonequilibrium molecular dynamics (EMD and NEMD, respectively). Two state points of the argon-krypton mixture are considered, for which experimental values of the Soret coefficient are available. To attempt a comparison between simulations and experiments the common enthalpy-diffusion-free expression for the heat flux has been chosen. The comparison of the simulations with the experiments shows a remarkable agreement, for all the several utilized EMD and NEMD techniques (dynamical and stationary). The techniques, used over 0.3 micros of total simulation time span, are slow convergent but have comparable performances.
The melting curves of argon, krypton, and xenon were measured in a laser heated diamond-anvil cell to pressures of nearly 80 GPa reaching melting temperatures around 3300 K. For the three gases, we observed a considerable decrease in the melting slopes (dT/dP) from the predictions based on corresponding states scaling starting near 40, 30, and 20 GPa, respectively. The melting anomaly can be understood in terms of a model in which hcp stacking faults act as solutes in a binary system.
The yields of multiply charged ions produced by the cascading decay of doubly-inner-shell-ionized argon and krypton atoms are calculated via straightforward construction of de-excitation trees. The final-ion-charge spectra are found to be sensitive to the distribution of initial vacancies within K and L shells.
Trans-scleral cyclophotocoagulation is an efficacious method in neovascular glaucoma (NVG) treatment. We have used it with krypton laser on 12 eyes of 12 patients affected by NVG with algetic symptoms. Six months after treatment, intraocular pressure was down enough for the pain to disappear. Executional simplicity and the possibility of modulating the intensity of the treatment are grounds for the encouragement of the technique's use in NVG.
The restoration of the outer blood-retinal barrier following krypton laser injury to the rat retina was studied at small and large laser lesions using intravenously injected sodium fluorescein, horseradish peroxidase, and catalase. The regenerated choriocapillaris and new blood vessels were permeable to fluorescein and peroxidase, but not to catalase. The regenerating retinal pigment epithelium gradually reformed a continuous sheet of cells covering all small laser sites and the periphery of large lesions. Zonulae occludens between the regenerated cells restored the outer retinal barrier and prevented diffusion of peroxidase into the retina. This occurred along Bruch's membrane and the new blood vessels that were covered by the regenerated pigment epithelial cells, but not in the center of the large lesion that was not relined by regenerated cells.
There has been a bewildering increase in the number and types of lasers available to the modern surgeon for the treatment of a variety of lesions. Pigmented and vascular lesions lend themselves to laser therapy and are common presentations in the cosmetic practice. While many different lasers may be effective for the treatment of these lesions, each has its own advantages and disadvantages. A detailed understanding of the specific properties and the applicability of the different lasers is vital if one is to successfully incorporate these lasers into one's practice. In this article, we discuss the different types of lasers available for the treatment of these lesions, discuss the specific indications and limitations and present our experience with the krypton laser.
The paper describes a morphologic picture of changes in eye tissues of rabbits in transconjunctival scleral action on the ciliary body by means of krypton laser (wavelength--647.1 nm) working in a continuous regime. The applications were located 1.0-1.5 mm from the limbus with energy--0.8--3.0 Wt, exposition time--2.0 sec., spot diameter--1000 mcm. The degree of necrosis of ciliary epithelium and atrophy of ciliary processes are directly dependent on the dose of action. Thus, the greatest part of laser radiation with 647.1 nm wavelength is absorbed at the level of the ciliary body. In perspective, this can lead to development of new methods for treatment of some eye diseases, such as glaucoma, tumors of the uveal tract, etc.
The regeneration of the retinal pigment epithelial (RPE) cells and their relationship with the vascular endothelium were studied during the healing of laser burns produced by krypton laser photocoagulation in rats. During the healing process the epithelial sheet was reformed by a morphologically heterogeneous population of RPE cells, some of which resembled macrophages. There seems to be a correlation between the specific phenotype of the regenerated RPE cell and the state of vitality of the adjacent endothelium. This was particularly evident in the scattered foci of choroidal subretinal neovascularization surrounded by RPE cells. One possible explanation for this apparent correlation is that the cytologic variations of the RPE cells reflect the multiple functions of a single cell which is expressed differently in different situations and in the course of interaction with other cells. This presumed ability of RPE cells may explain an intriguing aspect of cell-cell interaction, namely, the dual stimulatory and inhibitory effects of RPE cells on the vascular endothelium.
Laser treatment of a subretinal neovascular membrane associated with a unilateral choroidal osteoma in a 28-year-old woman is described. To our knowledge, this is the first reported use of krypton red laser photocoagulation for the initial treatment of a subfoveal neovascular membrane in this setting. Early recognition of the membrane allowed treatment prior to involvement of the central fovea. Follow-up has shown obliteration of the membrane without recurrence and 20/20 vision. We emphasize recognition of this unusual tumor, self-monitoring with an Amsler grid, and early treatment of subretinal neovascularization in this high risk group of young patients.
Ten (10) cases of macular choroidal neovascular membrane were treated successfully with krypton red laser (KRL) photocoagulation. The patients were followed up 3-15 months with no recurrence. Choroidal neovascular membranes outside the foveal region carried good visual prognosis, while poor visual outcome accompanied foveal involvement. The authors were encouraged by the efficacy of KRL photocoagulation in the treatment of macular choroidal neovascular membranes. Complications were few; however, the laser parameters, especially the output power, were key points to success.