Journal of Neurological Sciences 148 (1997) 53–65 Binocular saccadic eye movements in multiple sclerosis a b a a b J.P. Flipse , C.S.M. Straathof , J. Van der Steen , A.F. Van Leeuwen , P.A. Van Doorn , b a, * ´ F.G.A. Van der Meche , H. Collewijn a Department of Physiology, Faculty of Medicine, Erasmus University Rotterdam, P .O. Box 1738, NL-3000 DR Rotterdam, The Netherlands b Department of Neurology, Faculty of Medicine, Erasmus University Rotterdam, P .O. Box 1738, NL-3000 DR Rotterdam, The Netherlands Received 7 August 1996; accepted 29 October 1996 Abstract We attempted to increase the sensitivity for detection of abnormal binocular saccadic eye movements, particularly of the internuclear ophthalmoplegia (INO) type associated with multiple sclerosis (MS). Saccades of 10 and 208 were binocularly recorded with scleral sensor coils in 10 normal control subjects and 26 patients with definite or probable MS, seven of whom had a clinically manifest INO in one or both directions. In the cases in which this was accompanied by a dissociated nystagmus of the abducting eye, our recordings showed that such secondary saccades were also expressed, in a strongly reduced form, by the adducting eye. The patients with manifest INO showed lower average peak velocities and peak accelerations, especially for adduction of the eye on the affected side, but the distribution of these parameters overlapped with the normal distribution. A much sharper distinction between 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 inter-individual variability, had a narrow range in normals, and all values for INOs were outside this range. On this basis, the 19 patients without clinically manifest INO were easily separated into subgroups of 14 patients with completely normal interocular ratios and five patients with elevated peak velocity and acceleration ratios, identified as sub-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 particular, the acceleration of the adducting eye is strongly reduced in patients with an INO, and that this reduction is best identified by interocular comparison between binocular pairs of saccades.  1997 Elsevier Science B.V. Keywords: Multiple sclerosis; Eye movements; Saccades; Binocular; Internuclear ophthalmoplegia; Subclinical 1. Introduction same time, detection of a second (possibly subclinical) lesion is of paramount importance in order to obtain a The diagnosis of multiple sclerosis (MS) is based on definite diagnosis. Because a rather large part of the central clinical criteria. In addition to neurological examination nervous system is involved in visual-oculomotor activity, a and magnetic resonance imaging (MRI), a wide range of randomly located MS lesion will frequently cause (tran- paraclinical tests support the diagnosis, which rests pre- sient) visual or oculomotor disturbances. Therefore, a dominantly on objective evidence concerning two separate study of eye movements may assist in demonstrating lesions in the central nervous system (Poser et al., 1983). neurological dysfunction attributable to lesions that are In case two clinically distinct lesions do not occur at the clinically silent as such. The literature shows that many MS patients develop some form of oculomotor dysfunction at some stage of the disease (Baloh et al., 1978; Mastaglia et al., 1979; Tackmann et al., 1980; Reulen et al., 1983; ¨ * Muri and Meienberg, 1985; Meienberg et al., 1986; for Corresponding author. Tel: 131 10 4087560; fax: 131 10 4367594; e-mail: collewijn@fys1.fgg.eur.NL. review see Leigh and Zee, 1991). 0022-510X / 97 / $17.00  1997 Elsevier Science B.V. All rights reserved PII S0022-510X(96)05330-0