A new measure of dysconjugacy in INO: the first-pass amplitude.
BACKGROUND
The ratios of abducting to adducting eye movements (versional dysconjugacy index, VDI) for saccadic velocity and acceleration have been useful measures by which to objectively characterize internuclear ophthalmoparesis (INO). Amplitude measures of dysconjugacy have been less useful, given that many patients maintain the ability to ultimately reach a centrifugal fixation target and that traditional amplitude measures of VDI have focused on this 'final amplitude' (FA) position.


METHODS
We utilized infrared oculography to define a new amplitude measure of dysconjugacy in 42 multiple sclerosis (MS) patients with INO. The first-pass amplitude (FPA)-VDI is the ratio of abduction/adduction eye movement amplitudes computed at the time when the abducting eye initially achieves the centrifugal horizontal fixation target.


RESULTS
FPA-VDI values were significantly more sensitive and specific than FA-VDI values in demonstrating dysconjugacy in INO, and there was a 14-fold increase in dysconjugacy as measured by FPA-VDI Z-scores when compared to FA-VDI Z-scores.


CONCLUSIONS
Consideration of velocity (pulse) and amplitude (step) components of dysconjugacy in patients with INO can provide a greater understanding of the dynamic aspects of this syndrome. We propose to characterize the relationship between the pathophysiology of INO and neuroradiologic measures of tissue injury in MS.
Frohman
Elliot M
EM
Department of Neurology, University of Texas Southwestern Medical Center at Dallas, 5323 Harry Hines Blvd., Dallas, TX 75235, USA. elliot.frohman@utsouthwestern.edu
O'Suilleabhain
Padraig
P
Dewey
Richard B
RB
Frohman
Teresa C
TC
Kramer
Phillip D
PD
D003941:Diagnostic Techniques, Ophthalmological; D004585:Electrooculography / Q000379:methods; D005133:Eye Movements; D005403:Fixation, Ocular / Q000502:physiology; D006801:Humans; D009103:Multiple Sclerosis / Q000150:complications / Q000503:physiopathology*; D015835:Ocular Motility Disorders / Q000175:diagnosis / Q000209:etiology / Q000503:physiopathology*; D011930:Reaction Time; D012680:Sensitivity and Specificity; D014894:Weights and Measures