10. Nystagmus and other ocular motor oscillations and intrusions
نویسنده
چکیده
In Volume 1 , this chapter ( 1 ) contained a definition and at least one relevant reference for each type of nystagmus, saccadic oscillation or saccadic intrusion. Table 1 lists the 41 different types of nystagmus along with 64 other terms found in the l iterature to describe them ; similarly, Table 2 lists the 1 6 saccadic oscilla tions and intrusions with 27 other terms found in the literature. These Tables evolved from those which appeared in Volume 2 (2) and contain the following changes: In Table 1 , 'ictal' has been included under Epileptic nystagmus ; 'monocu lar fixation' under Latent/Manifest latent nystagmus ; 'kinetic' , 'optic' , 'optomo tor' , 'panoramic' , 'railway' , 'sigma', and 'train' under Optokinetic nystagmus . In Table 2, 'dipping' and ' inverse' have been included under Bobbing ; 'Double saccadic pulses' replaces Saccadic double pulses ; and 'Psychogenic flutter' re places Voluntary 'nystagmus' as a specific type of saccadic oscillation with 'hysteri cal flutter' and 'voluntary flutter' added to this category. No doubt this evolution, which has resulted from quantitative oculography, will continue as we learn more. I have developed the definitions and categorizations used herein, and initially presented in Volume 1 , by the systematic application of criteria derived from accurate ocular motility recordings made during the past 1 5 years by other investi gators and myself. Such criteria clearly differentiate between nystagmus and other ocular motor oscillations and, as a result, some eye movements described by the word 'nystagmus' were found to be saccadic oscillations. Most oscillations were originally named without the benefits of accurate ocular motor recordings (the naming preceded the understanding) . Quotation marks are used for those oscilla tions that are not truly nystagmus or for purely subjective clinical terms found in the literature which are inadequate, not clearly defined, or have been misapplied to several different types of oscillations. Since these ambiguous and/or erroneous terms do not convey accurate information about the basic nature of the movement, they are better left at the bedside and not imposed upon the scientific literature. In those cases where historical precedence supports their continued usage (conver gence-retraction 'nystagmus'), the quotation marks indicate that these are non-nys tagmic oscillations (i .e . saccadic) . I hope, for the reader's sake, that future investi gators will be more reluctant to use subjective clinical expressions to describe oscil lating eyes, and will take more care to identify proper�y an oscillation as one of the main (numbered) types listed in Tables 1 and 2. Obviously, this can only be
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