Eye Tracking and Saccade Testing in Progressive Supranuclear Palsy

Overview

Eye movement abnormalities are among the most characteristic and diagnostically valuable features of Progressive Supranuclear Palsy (PSP), a 4R-tauopathy that causes progressive postural instability, vertical supranuclear gaze palsy, and cognitive impairment. Oculomotor dysfunction in PSP results from degeneration of the brainstem nuclei and cortical pathways controlling eye movements, particularly affecting vertical saccades. This page provides a comprehensive guide to eye tracking and saccade testing for PSP diagnosis, covering key abnormalities, testing protocols, diagnostic criteria, and differential diagnosis. [@litvan1994]

Pathophysiology of Oculomotor Dysfunction in PSP

The oculomotor abnormalities in PSP arise from selective vulnerability of specific neuronal populations: [@golbe2008]

Brainstem Structures Affected

| Structure | Function | PSP Pathology | [@research]
|-----------|----------|---------------| [@tobii]
| [Midbrain](/brain-regions/midbrain) | Vertical gaze control | Tau-positive neuropil threads, neuronal loss |
| Superior colliculus | Saccade generation | Degeneration of intermediate layers |
| Rostral interstitial MLF | Vertical saccade control | Neurofibrillary tangles |
| Pontine omnipause neurons | Saccade gating | Cell loss |
| [Substantia nigra](/brain-regions/substantia-nigra) | Eye movement modulation | Dopaminergic neuron loss |

Cortical Pathways

Overview

Eye movement abnormalities are among the most characteristic and diagnostically valuable features of Progressive Supranuclear Palsy (PSP), a 4R-tauopathy that causes progressive postural instability, vertical supranuclear gaze palsy, and cognitive impairment. Oculomotor dysfunction in PSP results from degeneration of the brainstem nuclei and cortical pathways controlling eye movements, particularly affecting vertical saccades. This page provides a comprehensive guide to eye tracking and saccade testing for PSP diagnosis, covering key abnormalities, testing protocols, diagnostic criteria, and differential diagnosis. [@litvan1994]

Pathophysiology of Oculomotor Dysfunction in PSP

The oculomotor abnormalities in PSP arise from selective vulnerability of specific neuronal populations: [@golbe2008]

Brainstem Structures Affected

| Structure | Function | PSP Pathology | [@research]
|-----------|----------|---------------| [@tobii]
| [Midbrain](/brain-regions/midbrain) | Vertical gaze control | Tau-positive neuropil threads, neuronal loss |
| Superior colliculus | Saccade generation | Degeneration of intermediate layers |
| Rostral interstitial MLF | Vertical saccade control | Neurofibrillary tangles |
| Pontine omnipause neurons | Saccade gating | Cell loss |
| [Substantia nigra](/brain-regions/substantia-nigra) | Eye movement modulation | Dopaminergic neuron loss |

Cortical Pathways

The cortical gaze control system includes the [frontal eye fields](/brain-regions/prefrontal-cortex), supplementary eye fields, and parietal cortex. In PSP, these frontal lobe regions show early tau pathology, contributing to saccadic dysfunction.

Key Oculomotor Abnormalities

Vertical Supranuclear Gaze Palsy (VSGP)

VSGP is the cardinal eye movement abnormality in PSP and a core diagnostic feature in the MDS-PSP criteria [1].

Clinical Characteristics

• Initial presentation: Difficulty with downward gaze, particularly when looking down to read or navigate stairs
• Progression: Upward gaze affected next, followed by horizontal saccades
• Preservation: Vestibular ocular reflex (VOR) remains intact early—patients can voluntarily move eyes using vestibular input

Quantitative Measures

| Parameter | Normal | PSP | Clinical Significance |
|-----------|--------|-----|----------------------|
| Vertical saccade velocity | >400°/s | <200°/s | Key discriminator |
| Vertical saccade latency | <250ms | >350ms | Early finding |
| Saccadic accuracy | >95% | <80% | Hypermetria/hypometria |
| Smooth pursuit gain | >0.9 | <0.6 | Vertical > horizontal |

Eyelid Opening Apraxia (Blepharospasm)

Eyelid opening apraxia is a distinctive feature of PSP that helps differentiate it from other parkinsonian disorders [2].

Clinical Features

• Inability to voluntarily open eyelids despite intact levator palpebrae function
• Delayed initiation of eyelid opening after attempted voluntary opening
• Levodopa responsiveness: Often improves with dopaminergic therapy initially
• Concurrent blepharospasm: Involuntary eyelid closure may coexist

Testing Protocol

Square Wave Jerks

Square wave jerks (SWJs) are involuntary saccadic intrusions that interrupt fixation and are highly characteristic of PSP [3].

Characteristics

• Pattern: Pairs of saccades away from fixation, followed by return
• Amplitude: Typically 1-5 degrees
• Frequency: More frequent in PSP than in PD or CBS
• Distribution: Present in primary position during fixation

Clinical Significance

• High specificity for PSP among atypical parkinsonisms
• Frequency correlates with disease severity and midbrain atrophy
• Differentiates PSP from PD where SWJs are uncommon

Testing Protocol

Standard Oculomotor Examination

Equipment Required

• [ ] Visual acuity chart (near and distance)
• [ ] Standard examining scope or target
• [ ] Infrared or video oculography (research settings)
• [ ] Electromyography of levator palpebrae (research settings)

Examination Sequence

Bedside Testing Protocol

Vertical Saccade Assessment:

Quantitative Oculography

For research and detailed clinical assessment, quantitative measures provide superior sensitivity:

| Measure | Technique | PSP Finding |
|--------|-----------|-------------|
| Saccade velocity | Infrared eye tracking | Marked reduction in vertical saccades |
| Saccade latency | Video-oculography | Prolonged latency, especially vertical |
| Antisaccade task | Interactive paradigm | High error rate (>50%) |
| Memory-guided saccades | Delayed target paradigm | Impaired accuracy |

MDS-PSP Diagnostic Criteria

The Movement Disorder Society-PSP criteria (MDS-PSP 2017) incorporate oculomotor findings as core diagnostic features [1]:

Core Clinical Features

| Feature | Points | Description |
|---------|--------|-------------|
| VSGP | 4 | Vertical supranuclear gaze palsy, downward > upward |
| VSGP or slow vertical saccades | 2 | Either VSGP or reduced vertical saccade velocity |

Suggestive Features

| Feature | Points | Description |
|---------|--------|-------------|
| Eyelid opening apraxia | 1 | Inability to open eyes voluntarily |
| Excessive square wave jerks | 1 | Frequent SWJs during fixation |

Diagnostic Levels

• Probable PSP: VSGP + postural instability within 1 year
• Possible PSP: VSGP or other core feature without certainty
• Laboratory-supported PSP: Specific biomarker patterns

Historical Criteria (NINDS-SPSP)

The original NINDS-SPSP (National Institute of Neurological Disorders and Stroke-PSP Scientific) criteria from 1994 established the first standardized diagnostic framework for PSP [4]. While largely superseded by MDS-PSP criteria, the NINDS-SPSP remains important for historical comparison and certain research contexts:

| Criterion | Description |
|-----------|-------------|
| Possible PSP | Vertical supranuclear gaze palsy OR vertical saccade slowing + postural instability |
| Probable PSP | Vertical supranuclear gaze palsy + postural instability within 1 year |

The MDS-PSP criteria improved on NINDS-SPSP by adding suggestive features, biomarker support, and variant-specific criteria.

Differential Diagnosis

PSP vs. Parkinson's Disease

| Oculomotor Feature | PSP | Parkinson's Disease |
|--------------------|-----|----------------------|
| Vertical saccade slowing | Present early (core feature) | Present late or absent |
| Square wave jerks | Common, frequent | Uncommon |
| Eyelid opening apraxia | Common | Rare |
| Blink rate | Reduced | Increased (early) |
| VOR | Preserved | Preserved |

PSP vs. Corticobasal Syndrome

| Oculomotor Feature | PSP | CBS |
|--------------------|-----|-----|
| Vertical saccade slowing | Universal, early | Less common |
| Horizontal saccades | Affected later | Asymmetric impairment |
| Eyelid apraxia | Common | Variable |
| Alien limb | Rare | Common |
| Apraxia | Less prominent | Prominent |

PSP vs. Multiple System Atrophy

| Oculomotor Feature | PSP | MSA |
|--------------------|-----|-----|
| VSGP | Core feature | Late or absent |
| Saccadic pursuit | Variable | Prominent |
| Oculomotor palsy | Vertical > horizontal | Variable |

Clinical Utility

Diagnostic Accuracy

• VSGP has high specificity (>90%) for PSP among parkinsonian disorders
• Vertical saccade velocity <200°/s differentiates PSP from PD with high sensitivity
• Square wave jerks are more frequent in PSP than in any other parkinsonism

Prognostic Value

• Early VSGP predicts more rapid progression
• Severe oculomotor impairment correlates with shorter survival
• Eyelid opening apraxia indicates advanced brainstem involvement

Correlation with Disease Severity

Oculomotor measures correlate with clinical staging and disease progression in PSP:

| Measure | Correlation | Clinical Implication |
|---------|-------------|---------------------|
| Vertical saccade velocity | PSPRS score (r = -0.65) | Lower velocity = worse score |
| Square wave jerk frequency | Midbrain atrophy (r = 0.58) | Higher frequency = more atrophy |
| Eyelid opening latency | Disease duration (r = 0.52) | Longer latency = longer disease |
| Antisaccade error rate | Frontal dysfunction (r = 0.70) | Higher errors = more cognitive impairment |

The Progressive Supranuclear Palsy Rating Scale (PSPRS) incorporates oculomotor items, and vertical saccade velocity decline parallels progression on this scale [7]. The PSPRS includes specific items for:

• Ocular motor examination (gaze palsy, saccade velocity)
• Eyelid function (opening apraxia, blepharospasm)
• Bulbar function (dysphagia, dysarthria)

Monitoring Disease Progression

Serial oculomotor examination provides objective measures for:

• Clinical trial outcomes
• Disease progression tracking
• Therapeutic response assessment

Commercial Eye Tracking Systems

EyeLink (SR Research Ltd.)

The EyeLink series is a widely used video-based eye tracking system in neurological research and clinical trials [6].

| Model | Sampling Rate | Features | Clinical Use |
|-------|--------------|----------|--------------|
| EyeLink 1000 Plus | 2000 Hz | High precision, monocular/binocular | Research-grade saccade measurement |
| EyeLink Portable | 500 Hz | Portable, laptop-based | Clinical screening |
| EyeLink Core | 250 Hz | Cost-effective | Bedside assessment |

Advantages for PSP

• High temporal resolution for measuring saccade velocity
• Validated normative data available
• Widely used in clinical trials

Other Commercial Systems

| System | Manufacturer | Key Features |
|--------|--------------|--------------|
| Discovery | Arrington Research | Modular setup, high accuracy |
| iView X | SensoMotoric Instruments (SMI) | Integrated with VR systems |
| Tobii Pro | Tobii Technology | Remote eye tracking, large sample pools |
| Gazepoint | Gazepoint | Consumer-grade, research capable |

Associated Findings

Brain Imaging Correlates

• Midbrain atrophy on MRI correlates with vertical saccade impairment
• Superior cerebellar peduncle degeneration on DTI correlates with saccadic dysfunction
• Hummingbird sign on midsagittal MRI suggests advanced disease

Other Neurological Findings

• Frontal lobe signs often co-occur with oculomotor impairment
• Postural instability within first year strongly supports PSP when combined with VSGP
• Dysarthria and dysphagia progression parallels oculomotor decline

Cost and Accessibility

Commercial Systems

| System | Manufacturer | Features | Approximate Cost |
|--------|--------------|----------|-----------------|
| EyeLink 1000 Plus | SR Research Ltd. | High-speed infrared eye tracking, 1000Hz sampling | $15,000-25,000 |
| EyeLink Portable Duo | SR Research Ltd. | Portable option, 250Hz | $8,000-12,000 |
| EyeTribe | The EyeTribe | Consumer-grade, 60Hz | $1,000-2,000 |
| Tobii Pro Fusion | Tobii | 500Hz, research-grade | $20,000-35,000 |
| Tobii Pro Spectrum | Tobii | 600Hz, binocular | $30,000-45,000 |
| iScreen | Applied Science Laboratories | Clinical oculography | $10,000-18,000 |

Research vs. Clinical Use

• Research settings: Typically use high-speed systems (250-1000Hz) for precise measurement of saccadic velocity
• Clinical screening: Can use lower-cost video-oculography (60-120Hz) or even bedside testing
• Remote/telemedicine: Some systems allow home-based monitoring with webcams

Typical Costs for Clinical Assessment

| Component | Approximate Cost (USD) |
|-----------|----------------------|
| Quantitative oculography | $500-1,500 |
| Neurology consultation | $200-500 |
| Research protocol (academic center) | Often free for study participation |
| Serial monitoring (3 visits/year) | $1,500-4,500 |

Where to Get Tested

Academic movement disorder centers:

• UCSF Memory and Aging Center (Adam Boxer)
• Columbia University Movement Disorders
• Mayo Clinic Rochester
• University of Pennsylvania (David Irwin)
• UCL Queen Square (Huw Morris)

• CurePSP centers of care
• Michael J. Fox Foundation LRRK2 Consortium
• PSP Study Group clinical trials

Insurance Coverage

Most insurance plans cover oculomotor testing when clinically indicated for differential diagnosis. Pre-authorization may be required. Research protocols may offer free testing as part of clinical trials.

See Also

• [Progressive Supranuclear Palsy - Disease](/diseases/progressive-supranuclear-palsy)
• [Progressive Supranuclear Palsy - Diagnostic Methods](/diagnostics/progressive-supranuclear-palsy-methods)
• [Corticobasal Syndrome - Diagnostics](/diagnostics/cortico-basal-syndrome-methods)
• [Parkinson's Disease - Oculomotor Function](/diagnostics/parkinsons-disease-methods)
• [Tauopathies - Mechanisms](/mechanisms/tauopathies)
• [Brainstem - Brain Regions](/brain-regions/brainstem)
• [Ocular Motor Dysfunction - Mechanisms](/mechanisms/psp-ocular-motor-dysfunction)
• [PSP Vestibular-Ocular Reflex Deficits](/mechanisms/psp-vestibular-ocular-reflex-deficits)
• [Personalized Treatment Plan - Atypical Parkinsonism](/therapeutics/personalized-treatment-plan-atypical-parkinsonism)

Related Pages

• [Progressive Supranuclear Palsy](/diseases/progressive-supranuclear-palsy)
• Personalized Treatment Plan - Atypical Parkinsonism
• [Proteins: Tau](/proteins/tau)
• [Mechanisms: Tauopathies](/proteins/tau)
• Diagnostics: Digital Biomarkers
• [Therapeutics: Exercise for PSP](/diseases/progressive-supranuclear-palsy)

References

Pathway Diagram

The following diagram shows the key molecular relationships involving Eye Tracking and Saccade Testing in Progressive Supranuclear Palsy discovered through SciDEX knowledge graph analysis: