BINOCULAR SACCADIC EYE-MOVEMENTS IN MULTIPLE-SCLEROSIS

We attempted to increase the sensitivity for detection of abnormal bin ocular saccadic eye movements, particularly of the internuclear ophtha lmoplegia (INO) type associated with multiple sclerosis (MS). Saccades of 10 and 20 degrees were binocularly recorded with scleral sensor co ils in 10 normal control subjects and 26 patients with definite or pro bable MS, seven of whom had a clinically manifest INO in one or both d irections. In the cases in which this was accompanied by a dissociated nystagmus of the abducting eye, our recordings showed that such secon dary saccades were also expressed, in a strongly reduced form, by the adducting eye. The patients with manifest INO showed lower average pea k velocities and peak accelerations, especially for adduction of the e ye on the affect-ed side, but the distribution of these parameters ove rlapped with the normal distribution. A much sharper distinction betwe en normals and patients with INOs was found by considering the ratios between peak accelerations and velocities of saccade pairs (abducting eye/adducting eye). These ratios, which eliminate much intra- and inte r-individual variability, had a narrow range in normals, and all value s for INOs were outside this range. On this basis, the 19 patients wit hout clinically manifest INO were easily separated into subgroups of 1 4 patients with completely normal interocular ratios and five patients with elevated peak velocity and acceleration ratios, identified as su b-clinical (uni- or bilateral) INOs. Measurements of vertical saccades and of interocular timing differences provided no useful criteria for disturbances of binocular coordination in MS. We conclude that in par ticular, the acceleration of the adducting eye is strongly reduced in patients with an INO, and that this reduction is best identified by in terocular comparison between binocular pairs of saccades. (C) 1997 Els evier Science B.V.