title: Familial voluntary nystagmus.
abstract: OBJECTIVE
  To examine the pathological significance and familial occurrence of voluntary nystagmus.
  
  
  METHODS
  We examined two families orthoptically as well as with video and search-coil techniques or electronystagmography (ENG). Three members of three generations of the first family and a 9-year-old boy from a second family not related to the first were able to generate a voluntary horizontal nystagmus.
  
  
  RESULTS
  The characteristics of the nystagmus of our original patient, his daughter and 8-year-old grandson (1st family) were remarkably similar: duration of 2-5 seconds, amplitudes of 1-4 degrees and frequencies around 15 cycles/second. In the second family, our patient with a congenital esotropia and hyperopia was the only one of his family who could voluntarily produce a nystagmus of about 5 degrees and 10 cycles/second for maximum of 20 seconds. During prolonged reading, the same nystagmus with disturbing oscillopsia developed involuntarily and was not suppressible. We added +0.75 diopters to both lenses of his spectacles to account for the result of our cycloplegic refraction. This stopped the involuntary nystagmus during near fixation.
  
  
  CONCLUSIONS
  To avoid unintentional "bouts" of voluntary nystagmus, a reduction of the convergence impulse by plus-lenses may be effective. The parameters of voluntary nystagmus can be considered family-specific.
authors.affiliation: Department of Ophthalmology, University Hospital, Lübeck, Germany. bneppert@ophtha.mu-luebeck.de
authors.forename: Birte
authors.initials: B
authors.lastname: Neppert
authors.forename: Holger
authors.initials: H
authors.lastname: Rambold
mesh_terms: D000368:Aged; D002648:Child; D004585:Electrooculography; D005133:Eye Movements / Q000502:physiology*; D020022:Genetic Predisposition to Disease; D006801:Humans; D008297:Male; D020417:Nystagmus, Congenital / Q000175:diagnosis / Q000235:genetics* / Q000503:physiopathology; D009801:Oculomotor Muscles / Q000503:physiopathology*; D010375:Pedigree