Retinal Injuries From Single and Multiple Picosecond Laser Pulses PDF Download
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Author: Carmen A. Puliafito
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Languages : en
Pages : 9
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We investigate laser-induced shock waves from melanin particles as a possible cause of retinal injury from ultrashort pulse laser exposures. Melanin granules were isolated from calf retina and suspended in gels. The melanin particles were irradiated with 100 psec laser pulses from an amplified, mode- locked Nd:YAG laser and shock waves were observed under a microscope using a time-delayed strobe pulse. Spherical shock fronts were observed at incident laser fluences 4J/sq cm and were imaged as close as 20 micrometers from the melanin particles. Multiple shock fronts were resolved when several melanin particles were irradiated simultaneously. Shock front radii were measured as a function of photographic delay time and laser fluence. Average shock from velocities during the first 10 nsec ranged from 2500 to 4000 m/sec. A velocity of 3000 m/sec corresponds to a shock pressure of 11 kbars. These results indicate that shock wave emission from melanin particles in the retinal pigment epithelium is a potential cause of retinal injury from ultrashort laser pulses.
Author: Carmen A. Puliafito
Publisher:
ISBN:
Category :
Languages : en
Pages : 9
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We investigate laser-induced shock waves from melanin particles as a possible cause of retinal injury from ultrashort pulse laser exposures. Melanin granules were isolated from calf retina and suspended in gels. The melanin particles were irradiated with 100 psec laser pulses from an amplified, mode- locked Nd:YAG laser and shock waves were observed under a microscope using a time-delayed strobe pulse. Spherical shock fronts were observed at incident laser fluences 4J/sq cm and were imaged as close as 20 micrometers from the melanin particles. Multiple shock fronts were resolved when several melanin particles were irradiated simultaneously. Shock front radii were measured as a function of photographic delay time and laser fluence. Average shock from velocities during the first 10 nsec ranged from 2500 to 4000 m/sec. A velocity of 3000 m/sec corresponds to a shock pressure of 11 kbars. These results indicate that shock wave emission from melanin particles in the retinal pigment epithelium is a potential cause of retinal injury from ultrashort laser pulses.
Author: J. S. Connolly
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Languages : en
Pages : 84
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Retinal damage thresholds were determined for exposures of the maculae of rhesus monkeys to CW and repetitive-pulse trains of argon-ion laser radiation at 514.5 nm in the TEMoo mode. Single-pulse exposures were made at pulsewidths of 2, 10, 40, and 100 microsec and 1, 10, 100, and 500 msec. Repetitive-pulse exposures were made for 27 different combinations: train durations of 0.05, 0.5, 5, and 30 sec; pulse repetition frequencies from 0.10 Hz to 10 kHz and pulsewidths of 10, 40, and 100 microsec and 1 msec. Damage thresholds for mode-locked argon laser pulses at 104 MHz and 250 psec pulsewidth for pulse trains of 9.9-sec, 10-msec, and 10-microsec duration were also measured. For pulsewidths of 10 microsec, there is an apparent cumulative effect provided the repetition frequencies are in the range of approximately 0.1 to approximately 10 Hz. The retina is more sensitive to double-pulse exposures, by a factor of 2 to 3 relative to single-pulse thresholds, when the interpulse spacing is approximately 2.5 sec. Nonthermal damage mechanisms, involving a two-step, two-threshold process, may explain our results. Specifically, for double-pulse configurations, the first acts as a reversible photo-trigger which sensitizes the retina in preparation for the subsequent pulse. The elements of an empirical model have been assembled and appear to account satisfactorily for the observed double-pulse threshold data. (Author).
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Languages : en
Pages : 0
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In order to evaluate laser safety standards, Dr. Toth examined fluorescein angiograms (in some cases OCT) and fixed tissue sections and aided in defining exposure limits for pulse widths less than one nanosecond. In our initial short pulse study, we were concerned with the restriction to a single wavelength. To verify that the tissue effects were due to the pulse structure, we obtained data outside a single wavelength. We obtained from information from -530-nm and -1060nm wavelengths to compare to data obtained from previous studies of visible laser picosecond and femtosecond pulses. The type of lesions created with 530 and 1060-1064nm wavelengths were similar to the lesions created in the earlier 580-nm wavelength studies. This supported the theory that laser induced breakdown is one of the primary damage mechanisms for ultrashort laser pulses. Data from our studies was used by the American National Standard Institute in publications ANSI Z136.1, 'Safe Use of Lasers' (updated 2000) and ANSI Z136.3, 'Safe Use of Lasers in Health Care Facilities' (1996).
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Category : Aeronautics
Languages : en
Pages : 704
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Author: H. W Hemstreet (Jr)
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Category :
Languages : en
Pages : 47
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Retinal damage thresholds are discussed for exposure of rhesus maculae to continuous wave and repetitive-pulse trains of 1064-nm Nd:YAG laser radiation. For all single-pulse exposures and for repetitive pulses contained within a 0.05-sec train, retinal damage appears to be induced primarily by thermal mechanisms. For the longer pulse-train durations, a cumulative effect is apparent when the repetition frequencies are in the range of>1 to
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Category :
Languages : en
Pages : 24
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This study has examined the cumulative effects of multiple-pulse laser exposures in contributing to retinal damage via a thermal mechanism. Three sets of experiments have been conducted to determine the variation of multiple- pulse thresholds: With the interval between pulses; with the number of pulses in the pulse train when the interpulse interval is held constant; and with the retinal image size when both number of pulses and interpulse interval are invariant. In addition, thermal model calculations were carried out to compare model predictions with the experimental data. Conclusions from the experimental data are: (1) The threshold for a multiple-pulse train is related to that for an individual pulse in the train by a function of the number of pulses, but is independent of pulse-repetition frequency and pulse train length. This observation is in general accordance both with the thermal model predictions and with previously empirical models. (2) The additivity of multiple pulses is quantitatively similar for collimated and expanded laser beams incident at the eye. (3) The repair or recovery of laser-induced reversible retinal damage (i.e., sub-threshold with respect to the ophthalmoscopic lesion endpoint) is slow, having a time constant of the order of days. Thus, the cumulative nature of multiple-pulse or repeated exposures within a 24-hr period is relatively unaffected by the ongoing repair process; and only when repeated daily exposures are of concern does the repair process become a factor. Keywords: Laser damage; Retina.
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Category : Laser materials
Languages : en
Pages : 522
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Author:
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ISBN:
Category :
Languages : en
Pages : 38
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Exposure of the fovea to single or multiple pulses of coherent light (532 nm) can produce both transient and permanent changes in the eye's ability to resolve fine spatial detail. The immediate effects for extended duration exposures (>50 msec) are often large, producing acuity deficits as great as 90% of its pre-exposure level. The size of these deficits often reflect a total loss of foveal functioning although, depending upon the energy and duration of the exposure, these changes are reversible. Permanent changes in acuity can be noted in the absence of gross morphological damage and at power densities below the ED50 level provided the area of involvement is large. On the other hand, at power densities above the ED50 level, little if any permanent or consistent visual deficits are noted if the damage is restricted to relatively isolated areas within either the foveal or parafovea. Multiple pulses which increase the area of total involvement are more effective in permanently shifting postexposure acuity than are the single pulse conditions. Cumulative effects of repetitive exposures separate in time by as much as several al days are possible. The exact parameters of any observed loss in visual performance of course is dependent upon the discrimination task and its ability to depict subtle changes in the retina mosiac. Laser safety (MPE), Visual acuity, Nd/YAG, Rhesus monkey, Flash effects, Long-term visual deficits, Light-induced damage, RA 3.
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Category :
Languages : en
Pages : 21
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Previous studies in our laboratory have established that microbubble formation inside the RPE cells is the damage mechanism for single exposures of short laser pulses from 100 fsec to -1 micro sec. In the current project, we investigated the mechanism for multiple laser pulse injury to RPE cells using a new pump-probe setup. We also investigated the expression of heat shock proteins as potential a marker of sublethal injury following short pulse laser exposure. Finally, we developed a slitlamp based light scattering system for monitoring laser-induced bubble formation in vivo.
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Category :
Languages : en
Pages : 121
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Minimum visible lesion (MVL) threshold measurements at the retina for rhesus monkey eyes are reported for femtosecond, picosecond, and nanosecond single laser pulses using visible wavelengths. Estimates of the dose causing 50% probability for damage (ED50) are calculated for 1-hour and 24-hours postexposure as well as the 95% fiducial intervals for ED. The ED values are found to be dependent on both wavelength and pulsewidth, and for a single wavelength are, in general, lower for short pulsewidths, with the exception of values at the shortest pulsewidth of 90 fs at 580 nm. At 90 fs the ED(50) dosages were noted to increase slightly when compared with the 3-ps and 600-fs values, all three delivered at 580-nm wavelength. The 4-ns ED(50) value was more than double the value at 60 ps delivered at 532-nm wavelength. Fluorescein angiography was accomplished at 1-hour and 24-hours postexposure and did not demonstrate lower threshold for damage, which has been the case for MVLs created with longer pulse duration (greater than 1 ns) or for rabbit eyes at the same pulse-widths as measured in our laboratory.
