Abstract
Abstract: :
Background:Little is known about the exact nature of the torsional component of AN seen in patients with multiple sclerosis (MS). Purpose:To investigate the horizontal, vertical and torsional components of AN in patients with MS and to relate it to clinical characteristics. Methods:Horizontal vertical and torsional components were measured in 10 patients with AN due to MS using a three–dimensional pupil and iris tracking video oculography technique (Strabs system, Sensomotoric Instruments). Eye movements were recorded binocularly and monocularly while subjects viewed targets in the primary position, secondary and tertiary positions of gaze. Stimuli to elicit horizontal, vertical and torsional optokinetic nystagmus were also presented. Results:TN was present in 4 out of 10 patients tested (in 3 patients bilaterally). TN waveform was pendular in 3 patients and had a jerk waveform with constant velocity in the fourth patient. The TN ranged from 0.7º to 5º and varied in frequency by 1.2 to 4.7 Hz and was conjugate in one patient. TN represented the largest proportion of all three nystagmus components seen in 6 of the 8 eyes in these subjects. There was no correlation between the size of the TN present and the level of visual acuity. There was also no correlation detected when looking at the asymmetry in the type of nystagmus present either eye in all three dimensions and the asymmetry in visual acuity. However patients demonstrating disconjugate nystagmus in all three dimensions showed a larger difference in visual acuity between eyes. There was no change in TN in secondary and tertiary gaze positions in all four patients. Of the 6 patients without TN, 5 demonstrated a change in nystagmus in at least one secondary or tertiary gaze position. All of these patients demonstrated a unilateral or bilateral internuclear ophthalmoplegia (INO). There was no INO in all 4 patients that demonstrated TN. The patients that demonstrated a torsional component were more likely to demonstrate more disconjugate eye movements in all three dimensions between the two eyes compared to those who had nystagmus in the horizontal and vertical planes alone. Horizontal and vertical OKN was present in all patients however torsional OKN could not be demonstrated in all 10 patients. Conclusions:In our study torsional nystagmus was present in 40% of patients with AN due to MS. It can have dissociated or associated pendular or jerk waveforms. Torsional OKN could not be elicited in any of the patients. Interestingly, in our series, patients with a torsional nystagmus component did not have internuclear ophthalmoplegia.
Keywords: eye movements • nystagmus • ocular motor control