The Experts below are selected from a list of 51 Experts worldwide ranked by ideXlab platform
Karl Ulrich Bartzschmidt - One of the best experts on this subject based on the ideXlab platform.
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electrical stimulation a therapeutic strategy for retinal and optic nerve disease
Graefes Archive for Clinical and Experimental Ophthalmology, 2012Co-Authors: Florian Gekeler, Karl Ulrich BartzschmidtAbstract:Since Galvani’s experiments with frog legs in 1791, we know that neural tissue can be readily excited by electrical currents. Doctors have utilized the therapeutic potential of electricity ever since, with such lasting achievements as cardioversion and defibrillation. In ophthalmology, one of the earliest scientific mentions of electrical currents is from Henri Dor in 1873 [1]. He used complicated machines for the treatment of “amblyopia and amauroses”, “retinochoroiditis with pigment infiltration”, “glaucoma”, and “white optic atrophy” — following a tendency of a technology minded era when electrical currents were praised for all kinds of ailments. His experiments and studies, however, fell into oblivion in the following decades at the beginning of the twentieth century, with giant progress of scientific medical practice in many other areas. Electrical stimulation of the visual system was re-discovered in the 1970s for elicitation of visual percepts, or phosphenes, by supra-threshold stimulation [2]. These experiments constituted the basis for retinal implants which today allow patients to recognize letters and shapes in laboratory and natural settings [3, 4]. During the course of these trials, the therapeutic potential of subthreshold electrical stimulation was detected in 2004 by Chow [5] in patients carrying an inactive subretinal prosthesis which produced only sub-threshold currents. His patients experienced amelioration of their residual vision even in retinal areas far from the implant. This effect was attributed to the release of neurotrophic factors, and various groups worldwide started to explore the therapeutic potential in animal experiments and in human trials. For practical reasons — such as ease of use and availability — application of currents through Corneal Electrodes has been widely adopted since then, coining the term transCorneal electrical stimulation (TES). Various types of contact lens-Electrodes or DTL-Electrodes deliver currents to counter-Electrodes, usually integrated in the Corneal Electrode or on the periorbital skin, to ensure good transretinal currents. More than 20 peer-reviewed publications in PubMed in the last 5 years are evidence for this renewed interest in electrical stimulation of ocular tissue.
T D Lamb - One of the best experts on this subject based on the ideXlab platform.
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light adaptation and dark adaptation of human rod photoreceptors measured from the a wave of the electroretinogram
The Journal of Physiology, 1999Co-Authors: M M Thomas, T D LambAbstract:1We recorded the a-wave of the human electroretinogram from subjects with normal vision, using a Corneal Electrode and ganzfeld (full-field) light stimulation. From analysis of the rising phase of rod-isolated flash responses we determined the maximum size (amax) of the a-wave, a measure of the massed circulating current of the rods, and the amplification constant (A) of transduction within the rod photoreceptors. 2During light adaptation by steady backgrounds the maximal response was reduced, as reported previously. amax declined approximately as I0/(I0+IB), where IB is retinal illuminance and I0 is a constant. In different subjects I0 ranged from 40 to 100 trolands, with a mean of 70 trolands, corresponding to about 600 photoisomerizations s−1 per rod. (1 troland is the retinal illuminance that results when a surface luminance of 1 cd m−2 is viewed through a pupil area of 1 mm2.) The amplification constant A decreased only slightly in the presence of steady backgrounds. 3Following a full bleach amax recovered along an S-shaped curve over a period of 30 min. There was no detectable response for the first 5 min, and half-maximal recovery took 13-17 min. 4The apparent amplification constant decreased at early times after large bleaches. However, upon correction for reduced light absorption due to loss of pigment, with regeneration of rhodopsin occurring with a time constant of 9-15 min in different subjects, it appeared that the true value of A was probably unchanged by bleaching. 5The recovery of amax following a bleach could be converted into recovery of equivalent background intensity, using a ‘Crawford transformation’ derived from the light adaptation results. Following bleaches ranging from 10 to > 99 %, the equivalent background intensity decayed approximately exponentially, with a time constant of about 3 min. 6The time taken for amax to recover to a fixed proportion of its original level increased approximately linearly (rather than logarithmically) with fractional bleach, with a slope of about 12 min per 100 % bleach. Similar behaviour has previously been seen in psychophysical dark adaptation experiments, for the dependence of the ‘second component’ of recovery on the level of bleaching.
Florian Gekeler - One of the best experts on this subject based on the ideXlab platform.
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electrical stimulation a therapeutic strategy for retinal and optic nerve disease
Graefes Archive for Clinical and Experimental Ophthalmology, 2012Co-Authors: Florian Gekeler, Karl Ulrich BartzschmidtAbstract:Since Galvani’s experiments with frog legs in 1791, we know that neural tissue can be readily excited by electrical currents. Doctors have utilized the therapeutic potential of electricity ever since, with such lasting achievements as cardioversion and defibrillation. In ophthalmology, one of the earliest scientific mentions of electrical currents is from Henri Dor in 1873 [1]. He used complicated machines for the treatment of “amblyopia and amauroses”, “retinochoroiditis with pigment infiltration”, “glaucoma”, and “white optic atrophy” — following a tendency of a technology minded era when electrical currents were praised for all kinds of ailments. His experiments and studies, however, fell into oblivion in the following decades at the beginning of the twentieth century, with giant progress of scientific medical practice in many other areas. Electrical stimulation of the visual system was re-discovered in the 1970s for elicitation of visual percepts, or phosphenes, by supra-threshold stimulation [2]. These experiments constituted the basis for retinal implants which today allow patients to recognize letters and shapes in laboratory and natural settings [3, 4]. During the course of these trials, the therapeutic potential of subthreshold electrical stimulation was detected in 2004 by Chow [5] in patients carrying an inactive subretinal prosthesis which produced only sub-threshold currents. His patients experienced amelioration of their residual vision even in retinal areas far from the implant. This effect was attributed to the release of neurotrophic factors, and various groups worldwide started to explore the therapeutic potential in animal experiments and in human trials. For practical reasons — such as ease of use and availability — application of currents through Corneal Electrodes has been widely adopted since then, coining the term transCorneal electrical stimulation (TES). Various types of contact lens-Electrodes or DTL-Electrodes deliver currents to counter-Electrodes, usually integrated in the Corneal Electrode or on the periorbital skin, to ensure good transretinal currents. More than 20 peer-reviewed publications in PubMed in the last 5 years are evidence for this renewed interest in electrical stimulation of ocular tissue.
M M Thomas - One of the best experts on this subject based on the ideXlab platform.
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light adaptation and dark adaptation of human rod photoreceptors measured from the a wave of the electroretinogram
The Journal of Physiology, 1999Co-Authors: M M Thomas, T D LambAbstract:1We recorded the a-wave of the human electroretinogram from subjects with normal vision, using a Corneal Electrode and ganzfeld (full-field) light stimulation. From analysis of the rising phase of rod-isolated flash responses we determined the maximum size (amax) of the a-wave, a measure of the massed circulating current of the rods, and the amplification constant (A) of transduction within the rod photoreceptors. 2During light adaptation by steady backgrounds the maximal response was reduced, as reported previously. amax declined approximately as I0/(I0+IB), where IB is retinal illuminance and I0 is a constant. In different subjects I0 ranged from 40 to 100 trolands, with a mean of 70 trolands, corresponding to about 600 photoisomerizations s−1 per rod. (1 troland is the retinal illuminance that results when a surface luminance of 1 cd m−2 is viewed through a pupil area of 1 mm2.) The amplification constant A decreased only slightly in the presence of steady backgrounds. 3Following a full bleach amax recovered along an S-shaped curve over a period of 30 min. There was no detectable response for the first 5 min, and half-maximal recovery took 13-17 min. 4The apparent amplification constant decreased at early times after large bleaches. However, upon correction for reduced light absorption due to loss of pigment, with regeneration of rhodopsin occurring with a time constant of 9-15 min in different subjects, it appeared that the true value of A was probably unchanged by bleaching. 5The recovery of amax following a bleach could be converted into recovery of equivalent background intensity, using a ‘Crawford transformation’ derived from the light adaptation results. Following bleaches ranging from 10 to > 99 %, the equivalent background intensity decayed approximately exponentially, with a time constant of about 3 min. 6The time taken for amax to recover to a fixed proportion of its original level increased approximately linearly (rather than logarithmically) with fractional bleach, with a slope of about 12 min per 100 % bleach. Similar behaviour has previously been seen in psychophysical dark adaptation experiments, for the dependence of the ‘second component’ of recovery on the level of bleaching.
Elliot M Frohman - One of the best experts on this subject based on the ideXlab platform.
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assessment of multiple sclerosis patients with a known history of unilateral optic neuritis shows optic nerve head component loss in the fellow unaffected eye s58 004
Neurology, 2012Co-Authors: Amy Conger, Darrel Conger, Teresa C Frohman, Shin C Beh, Benjamin Greenberg, Laura J Balcer, Peter A Calabresi, Elliot M FrohmanAbstract:Objective: To assess whether optic nerve head component testing can reveal sub-clinical damage not detected by optical coherence tomography and visual acuity testing in otherwise healthy MS eyes. Background Optical coherence tomography has long been used to determine thinning of the retinal nerve fiber layer, and its corresponding relationship to vision loss; in particular, abnormalities of low contrast letter acuity or sensitivity. A modification in the stimulus characteristics of multifocal electroretinography generates the optic nerve head component potential; a physiologic signature that signifies the integrity of ganglion cell axonal transmission and the transformation of membrane to saltatory conduction as these axons traverse the lamina cribrosa and acquires oligodendrocyte derived myelin. Design/Methods: Patients with multiple sclerosis were recruited to participate in the study. Subjects underwent retinal nerve fiber layer testing by optical coherence tomography (Spectralis), GDx, high and low contrast visual acuity, and blue optic nerve head component testing. The optic nerve head component testing was performed using the Veris FMS3 stimulator with a Grass amplifier and Burrian-Allan bipolar Corneal Electrode. Infra-red fundus and optic nerve head monitoring were performed throughout the 9 minute recording to ensure fixation and proper nerve head placement. Results: Preliminary data shows a large number of multiple sclerosis patients who have normal visual acuity, visual fields, oct and fundus exams exhibit a higher number of lost optic nerve component waveforms when compared to patients without multiple sclerosis and/or patients with no known history of ophthalmic or neurologic disease. Conclusions: Testing the optic nerve head component can detect damage to previously considered healthy eyes. This method could be used to assess previous damage for upcoming trials of neuro-protective and neuro-regenerative drugs. Supported by: DADS Foundation, Viragh Family Foundation. Disclosure: Dr. Conger has nothing to disclose. Dr. Conger has nothing to disclose. Dr. Frohman has received personal compensation for activities with Biogen Idec and Teva Pharmaceuticals. Dr. Beh has nothing to disclose. Dr. Greenberg has received personal compensation for activities with DioGenix, Greater Good Foundation, Biogen Idec, Serono, Inc., Sanofi-Aventis Pharmaceuticals, Inc., the Multiple Sclerosis Association of America and Teva Neuroscience as a consultant and/or speaker. Dr. Greenberg holds stock and/or stock options in Diogeix. Dr. Greenberg has received research support from Guthy-Jackson Charitable Foundation, Amplimmune, Inc. and the Accelerated Cure Project. Dr. Balcer has received personal compensation for activities with Biogen Idec, Vaccinex and Bayer as a consultant and has received honoraria from Biogen Idec and Novartis. Dr. Calabresi has received personal compensation for activities with Teva, Biogen Idec, Novartis, Genzyme, Johnson & Johnson, and Vertex. Dr. Calabresi has received research support from Biogen Idec, Teva, EMD Serono, Vertex, Genentech, Abbott, and Bayer. Dr. Frohman has received personal compensation for activities with Biogen Idec, Teva Neuroscience, Acorda Therapeutics, Novartis, Astellas, and Abbott Laboratories, Inc.