Eye movement disorders in multiple sclerosis and optic neuritis.

Horizontal saccadic and smooth pursuit eye movements were studied in 84 patients with multiple sclerosis (MS) and 21 patients with optic neuritis (ON). The MS patients were clinically classified as 'definite', 'probable', or 'possible'; subclinical eye movement disorder was found in 80 per cent of the definite, 74 per cent of the probable and 60 per cent of the possible category. Five of the ON patients (25 per cent) showed a subclinical eye movement deficit; these 5 were young patients with a recent history of ON. In a group of 27 MS patients with symptoms of spinal cord involvement only, 14 showed subclinical oculomotor disorder indicating the involvement of cerebral structures in the demyelination process. A study of the correlation between specific eye movement parameters and results of visual evoked response (VER) tests revealed that saccadic latency or smooth pursuit abnormalities are not correlated with prolonged VER latencies (P-100 peak latency). This indicates that lesions beyond the primary visual pathway contribute substantially to both parameters of oculomotor dysfunction. A significant correlation was found between prolonged saccadic latency and smooth pursuit deficit. An explanation for this finding based on functional aspects of the saccadic and smooth pursuit systems and their mutual interaction is presented. The occurrence of internuclear ophthalmoplegia (INO) is significantly related to an increase of saccadic latency. This finding indicates that demyelination in the patients manifesting INO may not be restricted exclusively to one or both medial longitudinal fasciculi, but may extend to other brainstem structures which are functionally involved in the programming of saccades. The findings confirm the value of standardized objective examination of eye movements in the detection and clarification of subclinical lesions in the central nervous system of patients with an early diagnosis of MS or ON.