Visual System Neural Responses to Laser Exposure from Local Q-Switched Pulses and Extended Source CW Speckle Patterns PDF Download
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Author: Myron L. Wolbarsht
Publisher:
ISBN:
Category :
Languages : en
Pages : 58
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Book Description
The reports of retinal damage from exposure to short pulse laser energy without any visual perception have been reviewed. A series of experiments has been conducted in cats to test retinal function after such laser exposures using neurophysiological recordings from retinal ganglion cells. The receptive fields of the selected ganglion cells were in the area of laser exposure or immediately adjacent to it. Microsensor monitoring of retinal metabolic stability including pH and O2 levels following laser exposure was also attempted. Vigorous neural responses have been recorded from retinal ganglion cells following suprathreshold lesion producing laser exposures within the Ganglion cell receptive fields, or from nerve fibers at the optic disc. The disc recordings always showed responses from ganglion cells following suprathreshold stimulation levels sufficient to cause retinal lesions within the receptive field or in closely adjacent areas of the retina.
Author: Myron L. Wolbarsht
Publisher:
ISBN:
Category :
Languages : en
Pages : 58
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Book Description
The reports of retinal damage from exposure to short pulse laser energy without any visual perception have been reviewed. A series of experiments has been conducted in cats to test retinal function after such laser exposures using neurophysiological recordings from retinal ganglion cells. The receptive fields of the selected ganglion cells were in the area of laser exposure or immediately adjacent to it. Microsensor monitoring of retinal metabolic stability including pH and O2 levels following laser exposure was also attempted. Vigorous neural responses have been recorded from retinal ganglion cells following suprathreshold lesion producing laser exposures within the Ganglion cell receptive fields, or from nerve fibers at the optic disc. The disc recordings always showed responses from ganglion cells following suprathreshold stimulation levels sufficient to cause retinal lesions within the receptive field or in closely adjacent areas of the retina.
Author:
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ISBN:
Category : Science
Languages : en
Pages : 348
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Book Description
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Category : Government reports announcements & index
Languages : en
Pages : 1424
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Author:
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ISBN:
Category : Science
Languages : en
Pages : 1298
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Category : Power resources
Languages : en
Pages : 864
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Book Description
Semiannual, with semiannual and annual indexes. References to all scientific and technical literature coming from DOE, its laboratories, energy centers, and contractors. Includes all works deriving from DOE, other related government-sponsored information, and foreign nonnuclear information. Arranged under 39 categories, e.g., Biomedical sciences, basic studies; Biomedical sciences, applied studies; Health and safety; and Fusion energy. Entry gives bibliographical information and abstract. Corporate, author, subject, report number indexes.
Author: Randolph D. Glickman
Publisher:
ISBN:
Category :
Languages : en
Pages : 7
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Book Description
This article is the result of investigations of retinal function following low-level exposures from an Nd:glass laser, using in vivo recordings of ganglion cell activity from the rhesus monkey retina. Time-dependent effects of laser exposures on rhesus monkey retinal ganglion cells were studied with a Q-switched, doubled Nd:glass laser, which produced 20 nsec pulses of 530-nm light, and a continuous-wave (CW) argon laser (514.5 nm), which produced exposures of 0.1-msec to 0.1-sec duration. Ganglion cell activity was recorded in situ by means of an intraocular electrode. Ganglion cells exposed to a single 20-nsec exposure, at a sublesion intensity, produced a 60-90 sec discharge of action potentials and exhibited a 2 log or greater elevation of light threshold, depending on beam size and intensity. At equivalent energy levels, the longer exposures produced the same or slightly weaker effects. This result is not as straightforward as it seems. Submillisecond flashes bleach no more than 50% of the visual pigment because of photoregeneration. The Dowling-Rushton relation predicts that a 50% bleach should produce only a 1.5 log loss of cone sensitivity. Exposures longer than 1 msec should not photoregenerate pigment (ie, more pigment will be bleached for a given exposure intensity). In view of the probable differences in pigment bleaching, it appears that the Q-switched laser light adapts the cells out of proportion to the visual pigment actually bleached-a single-cell analogue of Rushton's 'theta' effect. Keywords: Q-switched lasers, Neodymium lasers, Argon lasers, Electrophysiology, Reprints. (KT).
Author: David I. Randolph
Publisher:
ISBN:
Category :
Languages : en
Pages : 11
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Book Description
The 20 nsec Q-switched ruby laser exposures centered on the fovea produced no immediate changes in the grating visual evoked potential for 50 and 500 micron spot sizes at two energy levels even when visible changes occurred at these sites. The findings may have been the result of the ruby laser wavelength, which was near the visual sensitivity limit of the eye, or of the single Q-switched pulse which may have occurred too quickly to produce an immediate and/or sustained change in the cortical response. The observed delayed effects and subsequent apparent recovery of the VEP may reflect the development of edema at the laser exposure site resulting in the desynchronization of the response for a period of time. This is followed by apparent recovery which was interpreted as recruitment of the spared retinal elements with subsequent neural re-entrainment at the cortical level.
Author: William P. Roach
Publisher: SPIE-International Society for Optical Engineering
ISBN:
Category : Eye
Languages : en
Pages : 694
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Book Description
This volume contains key papers that document the initial probing of the limits of subnanosecond pulses and the resulting discoveries of nonlinear effects. The papers tell the story of effects previously thought to be impossible to produce in tissue. If you read all the references carefully, you will see the studies evolve from speculation to experimentation to theory, and culminate in policy recommendations.
Author: Fred H. Previc
Publisher:
ISBN:
Category :
Languages : en
Pages : 14
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Book Description
A comparison between the effects of single and multiple laser pulse-trains of equivalent energy was performed. Visual evoked potentials (VEPS) recorded bipolarly from the visual cortex of two rhesus monkeys in response to a counterphasing grating were used to assess the magnitude of the visual loss following four types of exposures: single and multiple pulses with total energies equal to 50% and 500% of the maximum permissible exposure (MPE) standard for humans. The results showed that the effects of a series of laser flashes presented within 200ms are similar to those of a single laser flash whose energy is equivalent to the cumulative energy of the multiple-pulse exposure. Keywords include: Flashblindness; Laser radiobiology; Multiple pulse; Q-switched; Radiation effects; Rhesus monkey; Visual evoked potential.
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Category :
Languages : en
Pages : 0
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Book Description
Little is known about the effects of brief, repetitive laser pulses in the microsecond and sub-microsecond range on visual adaptation. Although it is generally acknowledged that, for pulsed light exposures from 1 to 150 ms, the total energy of a flash (intensity x duration) determines its brightness or adaptation potential, there are little data supporting this reciprocal relationship in human subjects. The purpose of this study was to compare the increment threshold for a spot target superimposed on an extended source image of a pulsed laser source, and to evaluate whether reciprocity holds. Eight subjects completed a method-of-adjustment determination of increment threshold for a 023 white test spot viewed superimposed on an extended source image (0.61) of a green (532 nm) laser beam. The laser pulse durations were 10 micro s, 100 micro s, 1 ms and 10 ms at 3 Hz and 10Hz. In addition, the effect of continuous wave (CW) exposure was determined. The time-average laser exposure was held constant across all the laser conditions. For the 3 Hz pulse condition, the threshold luminance was much lower than for the CW condition and there was no effect of pulse width, i.e. reciprocity was observed. However, thresholds for the 1 ms and 10 ms pulses at 10 Hz were higher than for the DW case, and this reciprocity failure was interrupted as a brightness enhancement effect More pulse durations and pulse rates must be studied before this failure can be more fully understood.
