Visual Evoked Potentials (VEPs)
Visual Evoked Potentials (VEPs)
Visual Evoked Potentials are neurophysiological recordings that assess the functional integrity of the visual pathways from the retina to the occipital cortex.
Key Points
- Non-invasive diagnostic test measuring electrical activity in the visual cortex
- Evaluates optic nerve function and visual pathway integrity
- Particularly useful in pre-verbal children and infants
- Can detect subclinical visual pathway dysfunction
- Helps monitor disease progression and treatment response
Primary Clinical Applications
- Optic Neuritis Assessment
- Diagnostic confirmation
- Disease progression monitoring
- Treatment response evaluation
- Demyelinating Disorders
- Multiple sclerosis diagnosis and monitoring
- Acute disseminated encephalomyelitis (ADEM)
- Subclinical involvement detection
- Developmental Assessment
- Visual pathway maturation evaluation
- Cortical visual impairment diagnosis
- Assessment of unexplained visual loss
Specific Pediatric Indications
- Suspected cortical visual impairment
- Delayed visual maturation
- Unexplained visual behavior
- Neurometabolic disorders
- Genetic conditions affecting vision
- Post-traumatic visual assessment
Recording Parameters
- Stimulus Types
- Pattern reversal (checkerboard) - most common
- Pattern onset/offset
- Flash VEP - for infants and uncooperative patients
- Equipment Setup
- Active electrode at Oz (occipital)
- Reference electrode at Fz (frontal)
- Ground electrode at Cz (vertex)
- Recording Conditions
- Darkened room with constant ambient lighting
- Fixed viewing distance (usually 70-100 cm)
- Proper refractive correction if needed
Key Components Measured
- N75 (N1) - first negative peak
- P100 (P1) - major positive peak
- Latency: normally 100 ± 10 ms in adults
- Amplitude: typically 5-10 µV
- N145 (N2) - second negative peak
Normal Findings
- Age-appropriate latencies and amplitudes
- Symmetric responses between eyes
- Well-defined waveform morphology
- Reproducible responses
Abnormal Patterns
- Delayed P100 Latency
- Indicates demyelination
- Common in optic neuritis
- Seen in multiple sclerosis
- Reduced Amplitude
- Suggests axonal loss
- Indicates optic atrophy
- Seen in compressive lesions
- Absent Responses
- Complete optic nerve dysfunction
- Severe visual pathway damage
- Technical factors need exclusion
Age-Specific Considerations
- Neonates and Infants
- Flash VEP preferred
- Longer latencies normal due to incomplete myelination
- Maturational changes continue through first year
- Toddlers and Young Children
- Pattern VEP possible with attention-getting techniques
- Modified protocols may be necessary
- Age-specific normative data essential
Practical Tips
- Session Preparation
- Child-friendly environment
- Engagement techniques ready
- Multiple short recording segments
- Quality Assurance
- Regular impedance checks
- Movement artifact monitoring
- Multiple recordings for reproducibility
