A Case of Congenital Nystagmus Showing Reversed Optokinetic Nystagmus

⋅Copyright c 2023 by The Korean Balance Society. ⋅This is an open access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. A 26-year-old man presented with abnormal eye movement detected during childhood. On examinations, left-beating spontaneous nystagmus and horizontal gaze-evoked nystagmus during visual fixation (Supplementary Video 1). Video-oculography revealed normal saccades and impaired smooth pursuit in the left direction. Notably, the optokinetic nystagmus was reversed (Fig. 1). Moreover, there were no significant findings in the caloric test, video head impulse test, vestibular evoked myogenic potentials and posturography assessments. Ophthalmologic examinations and brain magnetic imaging revealed unremarkable findings. Previous studies have shown that in patients with congenital ocular disease, reversed optokinetic nystagmus may appear to be either bilaterally or unilaterally [1]. The reversed optokinetic nystagmus can be explained in terms of shifts in the position of the null point which is orbital eye position at which eye velocity is zero of the nystagmus induced by the pursuit or optokinetic stimuli [2]. Reversed optokinetic nystagmus is primarily observed in individuals with congenital nystagmus but can also occur in cases of acquired neurological abnormalities in the central nervous system, cerebellum, or brainstem. The precise cause of congenital nystagmus has not been definitively identified, but it is understood to result from abnormal decussation during the neural pathway’s formation [3].