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CS10.1 Visual electrophysiology in retinal and optic nerve and cortical disorders
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Clinical Symposia / Clinical Neurophysiology 117 (2006) S5–S17
group. Two forms have been recognised in hyperekplexia; a major and a minor form. The major form of hyperekplexia is characterised by excessive startle reflexes, startle-induced stiff falls and continuous stiffness in the neonatal period. The cause of the major form is mainly genetic with mutations in the a1 subunit of the glycine receptor or related genes. Patients with the minor form suffer from excessive startle reflexes without signs of stiffness. The cause of the minor form is not genetic and largely unknown. Additional brainstem abnormalities point toward a symptomatic minor form, but in patients with a nonsymptomatic minor form the cause is difficult to establish. A startle-EMG study should be performed to determine whether the excessive response can be classified as a startle reflex. Neuropsychiatric startle disorders form the second group. In this group of patients excessive startling as well as behavioural features occur. Examples include culture-specific disorders such as the ’Jumping Frenchmen of Maine’ and anxiety disorders. Startle motor patterns have not been investigated in detail and therefore, neuropsychiatric startle syndromes can currently not be identified on specific features. The third group is formed by disorders in which startling stimuli can induce responses other than startle reflexes, for example startle-induced epilepsy and reticular reflex myoclonus. The phenomenology and pathophysiology of stimulus-induced disorders is diverse. Further electrophysiological studies of startle disorders are required and will lead to improved discrimination between the groups. doi:10.1016/j.clinph.2006.07.033
CS10.1 Visual electrophysiology in retinal and optic nerve and cortical disorders G. Harding Aston University, Neurosciences Research Institute, UK Visual electrophysiology, particularly the electroretinogram (ERG) and visual evoked potentials (VEP) can be used to highlight the location of lesions in the visual system. Monocular ERGs can indicate the integrity of rod, cone and ganglion systems in the retina utilising scotopic photopic and 30 Hz stimulation. Pattern ERG allow the separation of reception and ganglion function using the P50 and N95 responses. More recently, multifocal ERGs allow detailed analysis of separate retinal locations combining the detail of static perimetry with objective responses from the retina. Visual evoked potentials to flash and pattern stimulation have been used for 40 years to locate post-retinal lesions. By combining monocular stimulation with multichannel recordings it is possible to locate lesions as prechiasmal or optic nerve, chiasmal and post-chiasmal. The combination of these two techniques, the ERG and VEP allow lesions to be located at all levels of the visual system and allow objective evidence of functional visual loss. Combined ERGs and VEPs provide good indications of
outcome when traumatic injuries to the visual system occur. The ERG is indicative of a variety of retinal conditions including retinitis pigmentosa, cone-dystrophy, retinal detachment, occlusive retinal vascular disease and other conditions affecting the layers of the retina. Combined with VEP they are helpful in diagnosing macular degeneration and central serous retinopathy although in the latter case multifocal ERGs are better. The VEP has been used for many years for diagnosing acute optic neuritis or demyelinating disease although its pre-dominant value has been overtaken by improvements in MRI scanning. It must be remembered however that MRI reflects anatomy whereas evoked potentials represent function. More central conditions such as localised trauma to the occipital regions are represented in asymmetric responses, correlating with field defects. Other diffuse but discrete cortical changes, such as those in Alzheimer’s disease also affect the VEP delaying the flash response but preserving the latency of the pattern reversal response. Recently a novel antiepileptic drug, vigabatrin, has been shown to be associated with peripheral visual field losses which appear permanent and irreversible. Using ERGs, it has proved possible to separate the effects of receiving the drug from those correlated with the field defect. Cone-ganglion function has been shown to be affected and reflected in the amplitude of the 30 Hz response. In spite of findings of microvaculation in the myelin sheath of animals VEPS were unaffected and there is no evidence in anatomical studies that humans are affected. Other antiepileptic drugs also affect the ERG. The lack of affect of vigabatrin on the VEP became fortuitous in assessment of visual function in patients too young to be examined by perimetry. By utilising a divided pattern stimulus with separate reversal rates for central and peripheral fields it is possible to test children as young as three years for preservation of peripheral field function. Compliance with this test is extremely high, and the test has high sensitivity and specificity. The development of detailed visual stimuli such as the multifocal stimulus will increase the utility of both the ERG and the VEP. In addition the temporal resolutions of these techniques give them a massive advantage over the slow functional MRI. doi:10.1016/j.clinph.2006.07.034
CS10.2 Multifocal ERG in assessment of retinal disorders D. Keating, S. Parks Gartnavel General Hospital, ElectroDiagnostic Imaging Unit, UK Background: In recent years, multifocal electroretinography (mfERG) has added a new dimension to objective investigation of retinal disorders. The technique uses simultaneous stimulation of multiple retinal sites to obtain spatial information on retinal function. The stimulation sequence also contains multiple frequency components
Clinical Symposia / Clinical Neurophysiology 117 (2006) S5–S17
group. Two forms have been recognised in hyperekplexia; a major and a minor form. The major form of hyperekplexia is characterised by excessive startle reflexes, startle-induced stiff falls and continuous stiffness in the neonatal period. The cause of the major form is mainly genetic with mutations in the a1 subunit of the glycine receptor or related genes. Patients with the minor form suffer from excessive startle reflexes without signs of stiffness. The cause of the minor form is not genetic and largely unknown. Additional brainstem abnormalities point toward a symptomatic minor form, but in patients with a nonsymptomatic minor form the cause is difficult to establish. A startle-EMG study should be performed to determine whether the excessive response can be classified as a startle reflex. Neuropsychiatric startle disorders form the second group. In this group of patients excessive startling as well as behavioural features occur. Examples include culture-specific disorders such as the ’Jumping Frenchmen of Maine’ and anxiety disorders. Startle motor patterns have not been investigated in detail and therefore, neuropsychiatric startle syndromes can currently not be identified on specific features. The third group is formed by disorders in which startling stimuli can induce responses other than startle reflexes, for example startle-induced epilepsy and reticular reflex myoclonus. The phenomenology and pathophysiology of stimulus-induced disorders is diverse. Further electrophysiological studies of startle disorders are required and will lead to improved discrimination between the groups. doi:10.1016/j.clinph.2006.07.033
CS10.1 Visual electrophysiology in retinal and optic nerve and cortical disorders G. Harding Aston University, Neurosciences Research Institute, UK Visual electrophysiology, particularly the electroretinogram (ERG) and visual evoked potentials (VEP) can be used to highlight the location of lesions in the visual system. Monocular ERGs can indicate the integrity of rod, cone and ganglion systems in the retina utilising scotopic photopic and 30 Hz stimulation. Pattern ERG allow the separation of reception and ganglion function using the P50 and N95 responses. More recently, multifocal ERGs allow detailed analysis of separate retinal locations combining the detail of static perimetry with objective responses from the retina. Visual evoked potentials to flash and pattern stimulation have been used for 40 years to locate post-retinal lesions. By combining monocular stimulation with multichannel recordings it is possible to locate lesions as prechiasmal or optic nerve, chiasmal and post-chiasmal. The combination of these two techniques, the ERG and VEP allow lesions to be located at all levels of the visual system and allow objective evidence of functional visual loss. Combined ERGs and VEPs provide good indications of
outcome when traumatic injuries to the visual system occur. The ERG is indicative of a variety of retinal conditions including retinitis pigmentosa, cone-dystrophy, retinal detachment, occlusive retinal vascular disease and other conditions affecting the layers of the retina. Combined with VEP they are helpful in diagnosing macular degeneration and central serous retinopathy although in the latter case multifocal ERGs are better. The VEP has been used for many years for diagnosing acute optic neuritis or demyelinating disease although its pre-dominant value has been overtaken by improvements in MRI scanning. It must be remembered however that MRI reflects anatomy whereas evoked potentials represent function. More central conditions such as localised trauma to the occipital regions are represented in asymmetric responses, correlating with field defects. Other diffuse but discrete cortical changes, such as those in Alzheimer’s disease also affect the VEP delaying the flash response but preserving the latency of the pattern reversal response. Recently a novel antiepileptic drug, vigabatrin, has been shown to be associated with peripheral visual field losses which appear permanent and irreversible. Using ERGs, it has proved possible to separate the effects of receiving the drug from those correlated with the field defect. Cone-ganglion function has been shown to be affected and reflected in the amplitude of the 30 Hz response. In spite of findings of microvaculation in the myelin sheath of animals VEPS were unaffected and there is no evidence in anatomical studies that humans are affected. Other antiepileptic drugs also affect the ERG. The lack of affect of vigabatrin on the VEP became fortuitous in assessment of visual function in patients too young to be examined by perimetry. By utilising a divided pattern stimulus with separate reversal rates for central and peripheral fields it is possible to test children as young as three years for preservation of peripheral field function. Compliance with this test is extremely high, and the test has high sensitivity and specificity. The development of detailed visual stimuli such as the multifocal stimulus will increase the utility of both the ERG and the VEP. In addition the temporal resolutions of these techniques give them a massive advantage over the slow functional MRI. doi:10.1016/j.clinph.2006.07.034
CS10.2 Multifocal ERG in assessment of retinal disorders D. Keating, S. Parks Gartnavel General Hospital, ElectroDiagnostic Imaging Unit, UK Background: In recent years, multifocal electroretinography (mfERG) has added a new dimension to objective investigation of retinal disorders. The technique uses simultaneous stimulation of multiple retinal sites to obtain spatial information on retinal function. The stimulation sequence also contains multiple frequency components