saccadic intrusions
Abnormal fast eye movements that interrupt steady fixation, indicating dysfunction of brainstem or cerebellar eye movement control systems.
Full Definition
Saccadic intrusions are pathological fast eye movements that inappropriately interrupt steady fixation, representing dysfunction of the brainstem and cerebellar systems responsible for gaze stability. These abnormal movements include square wave jerks (small amplitude saccades away from and back to the target), macro square wave jerks (larger amplitude movements), and saccadic pulses (single movements away from fixation). Unlike nystagmus, saccadic intrusions are not rhythmic and do not have a slow phase component. They are commonly associated with cerebellar degeneration, progressive supranuclear palsy, Huntington's disease, and other neurodegenerative conditions. Patients may report difficulty with reading, visual tracking, or maintaining clear vision during fixation. The presence and pattern of saccadic intrusions can provide valuable localizing information about the underlying neurological disorder.
Usage
Usage note: Distinguish from rhythmic nystagmus; specify type when possible (square wave jerks, macro-saccades).
In Context
- "Frequent saccadic intrusions during attempted fixation suggested cerebellar dysfunction." — Eye movement examination
- "The patient's reading difficulties were attributed to prominent saccadic intrusions disrupting stable fixation." — Clinical correlation