Background: Classified as saccadic intrusions, Square-Wave Jerks (SWJs) have been observed during Visual Fixation (VF) in Alzheimer’s Disease (AD). However, the pathological significance of this phenomenon remains unclear. Objective: The present study analyzed the characteristics of SWJs in patients with AD with their eyes open in the dark without VF. Methods: Fifteen patients with AD and 15 healthy age- and sex-matched controls were investigated and compared. Saccadic intrusions with and without VF were detected as SWJs and measured using an electronystagmogram. Results: No significant difference in the frequency of SWJs was observed between control and AD groups with VF, but significantly more SWJs were observed in the AD group than in the control group in the absence of VF (p<0.01). In the control group, the frequency of SWJs was significantly higher with VF as compared to without VF. Conversely, the frequency in the AD group was significantly higher without VF. Furthermore, a directly proportional relationship was observed between the frequency of SWJs and higher-order function (R>0.55) in the AD group. Conclusion: SWJs without VF may have pathological significance in AD. In healthy individuals, SWJs are generated by VF and suppressed without VF. Conversely, in AD, SWJs are generated rather than suppressed in the absence of VF. These pathognomonic SWJs without VF also appear to be correlated with higher-order dysfunction, reflecting AD-related cortical damage. These findings suggest that pathological SWJs without VF observed in AD derive from cortical damage and may constitute an important marker of a higher-order function.

Trigeminal nerve disorder is an important neurological sign that is often seen with multiple sclerosis (MS). We investigated eye movements in three MS patients with trigeminal disorder due to pontine lesions near the trigeminal root entry zone (REZ). Upbeat nystagmus was observed in all MS patients with trigeminal REZ lesions. We conjecture that trigeminal nerve disorder and upbeat nystagmus appeared due to simultaneous damage to both the trigeminal nerve and the vestibulo-ocular reflex pathway. If upbeat nystagmus appears in MS patients exhibiting a trigeminal nerve disorder, such as trigeminal neuralgia, and paralysis, pontine lesions near the trigeminal REZ should be considered. Upbeat nystagmus can be understood as a useful sign for the clinical regional diagnosis of trigeminal nerve disorder.

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Glutamate receptor δ2 (GluRδ2) is expressed in the neuronal postsynaptic densities at the junctions between the Purkinje cells and the parallel fibers. Recent reports have described patients with opsoclonus who possess anti-GluRδ2 antibodies. We report the case of a 53-year-old man with opsoclonus whose cerebrospinal fluid was positive for anti-GluRδ2 antibodies. Electronystagmography revealed abnormal sinusoidal eye movements, which were definitively identified as opsoclonus. The frequency and amplitude of saccadic oscillations diminished after plasmapheresis (PE). The patient’s opsoclonus was altered after PE, suggesting that anti-GluRδ2 antibodies may act on the saccade generator in the brainstem via the cerebellum and that they may be involved in the onset of opsoclonus.

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