title: Quantitative oculographic characterisation of internuclear ophthalmoparesis in multiple sclerosis: the versional dysconjugacy index Z score.
abstract: BACKGROUND
  There is a poor correlation between multiple sclerosis disease activity, as measured by magnetic resonance imaging, and clinical disability.
  
  
  OBJECTIVE
  To establish oculographic criteria for the diagnosis and severity of internuclear ophthalmoparesis (INO), so that future studies can link the severity of ocular dysconjugacy with neuroradiological abnormalities within the dorsomedial brain stem tegmentum.
  
  
  METHODS
  The study involved 58 patients with multiple sclerosis and chronic INO and 40 normal subjects. Two dimensional infrared oculography was used to derive the versional dysconjugacy index (VDI)-the ratio of abducting to adducting eye movements for peak velocity and acceleration. Diagnostic criteria for the diagnosis and severity of INO were derived using a Z score and histogram analysis, which allowed comparisons of the VDI from multiple sclerosis patients and from a control population.
  
  
  RESULTS
  For a given saccade, the VDI was typically higher for acceleration v velocity, whereas the Z scores for velocity measures were always higher than values derived from comparable acceleration VDI measures; this was related to the greater variability of acceleration measures. Thus velocity was a more reliable measure from which to determine Z scores and thereby the criteria for INO and its level of severity. The mean (SD) value of the VDI velocity derived from 40 control subjects was 0.922 (0.072). The highest VDI for velocity from a normal control subject was 1.09, which was 2.33 SD above the normal control mean VDI. We therefore chose 2 SD beyond this value (that is, a Z score of 4.33) as the minimum criterion for the oculographic confirmation of INO. Of patients thought to have unilateral INO on clinical grounds, 70% (16/23) were found to have bilateral INO on oculographic assessment.
  
  
  CONCLUSIONS
  INO can be confirmed and characterised by level of severity using Z score analysis of quantitative oculography. Such assessments may be useful for linking the level of severity of a specific clinical disability with neuroradiological measures of brain tissue pathology in multiple sclerosis.
authors.affiliation: Department of Neurology, University of Texas Southwestern Medical Center, Dallas, Texas 75235, USA. efrohm@mednet.swmed.edu
authors.forename: E M
authors.initials: EM
authors.lastname: Frohman
authors.forename: T C
authors.initials: TC
authors.lastname: Frohman
authors.forename: P
authors.initials: P
authors.lastname: O'Suilleabhain
authors.forename: H
authors.initials: H
authors.lastname: Zhang
authors.forename: K
authors.initials: K
authors.lastname: Hawker
authors.forename: M K
authors.initials: MK
authors.lastname: Racke
authors.forename: W
authors.initials: W
authors.lastname: Frawley
authors.forename: J T
authors.initials: JT
authors.lastname: Phillips
authors.forename: P D
authors.initials: PD
authors.lastname: Kramer
mesh_terms: D016022:Case-Control Studies; D003941:Diagnostic Techniques, Ophthalmological; D006801:Humans; D009103:Multiple Sclerosis / Q000150:complications*; D015835:Ocular Motility Disorders / Q000209:etiology* / Q000503:physiopathology*; D012438:Saccades; D012720:Severity of Illness Index