Sign · 3
Saccades, pursuit & supranuclear gaze palsy
Beyond nystagmus and misalignment lies a third layer of central signs — broken smooth pursuit, intrusive saccades, and gaze palsies that preserve the reflex while abolishing the voluntary movement.
Smooth pursuit and saccadic intrusions
Following a slowly moving target should be smooth — the eyes glide along with it. When the cerebellum or its brainstem partners are damaged, the glide breaks into a staircase of small catch-up jerks (“saccadic pursuit”).
Sometimes extra saccades intrude when the patient is just trying to look steadily at one point. The most common kind are square-wave jerks: small horizontal hops that take the eye briefly off-target and back again.
Smooth pursuit draws on cortical eye fields, cerebellar flocculus and dorsal vermis, and brainstem nuclei that translate target velocity into matched eye velocity.1 Cerebellar disease replaces smooth pursuit with catch-up saccades; spinocerebellar ataxias, paraneoplastic syndromes, cerebellar stroke, and MS all do this.
Saccadic intrusions include square-wave jerks, macrosaccadic oscillations (hypermetric overshoots that swing about fixation, classically cerebellar), and opsoclonus (chaotic multidirectional saccades — paraneoplastic or post-viral).
Pursuit deficits alone are non-specific; their value is as the corroborating finding alongside GEN, dysmetric saccades, or skew, where they shift the differential decisively toward cerebellar disease. Quantitative video-oculography measures pursuit gain, latency, and saccadic intrusion rate, and is increasingly the way subtle cerebellar dysfunction is documented.
Healthy smooth pursuit: the eye traces the target with a near-overlapping sinusoid, lagging only a few milliseconds.
Square-wave jerks
Small paired horizontal saccades that take the eye briefly off-target, then bring it back.
- Seen in
- Cerebellar disease, PSP, normal at low frequency
Macrosaccadic oscillations
Large hypermetric saccades that swing about fixation, overshooting in each direction.
- Seen in
- Cerebellar fastigial nucleus lesions, paraneoplastic
Opsoclonus
Chaotic high-amplitude saccades in all directions with no intersaccadic interval.
- Seen in
- Paraneoplastic (neuroblastoma, lung), post-infectious
Supranuclear gaze palsy
A supranuclear gaze palsy is loss of voluntary eye movement with the reflexes intact. Ask the patient to look down — the eyes can't. Tip the head back instead, and the eyes promptly roll down. The lesion sits “above” the nerve nuclei that drive the eye muscles.
The supranuclear generators are the rostral interstitial nucleus of the MLF (riMLF — vertical/torsional saccades), the paramedian pontine reticular formation (PPRF — horizontal saccades), the cortical eye fields, superior colliculus, and basal ganglia. Their lesions abolish voluntary gaze but spare the VOR and oculocephalic reflex.4
Vertical supranuclear gaze palsy with falls and axial rigidity is the signature of progressive supranuclear palsy;2paramedian thalamic-mesencephalic stroke produces combined vertical gaze palsy, skew, and OTR.3 Pontine PPRF lesions produce horizontal gaze palsy; combined with the MLF, the result is the one-and-a-half syndrome.
Test voluntary saccades and pursuit in each plane, then check the oculocephalic reflex and Bell's phenomenon to confirm the supranuclear level. In PSP, slowed vertical saccades (square-wave jerks, hypometric downgaze) precede frank palsy by months; in vascular gaze palsies the onset is abrupt. Imaging targets the midbrain–thalamic junction; volumetric MRI may show midbrain atrophy in suspected PSP.