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Quantitative VEP analysis in children with cortical visual impairment
R Bencivenga1, P K Wong, S Woo
1Department of Diagnostic Neurophysiology, B.C.'s Children's Hospital, Vancouver, Canada.
Insights
New electrophysiologic measures derived from visual evoked potentials (VEP) can help diagnose cortical visual impairment (CVI) in children. Specific VEP-based "R values" show promise as objective diagnostic tools, particularly for children over five.
Area of Science:
- Neuroscience
- Ophthalmology
- Biomedical Engineering
Background:
- Cortical visual impairment (CVI) in children often presents typically, but objective electrophysiologic confirmation can be valuable.
- Existing diagnostic methods for CVI may benefit from supplementary objective measures.
Purpose of the Study:
- To investigate the utility of mathematically derived parameters from visual evoked potentials (VEP) for diagnosing CVI in children.
- To identify specific VEP-based metrics that can differentiate CVI patients from healthy controls.
Main Methods:
- Utilized 20-channel visual evoked potential (VEP) recordings from 30 children with CVI and 52 controls.
- Applied Hjorth's source derivation to VEP data to minimize reference contamination and enhance signal localization.
- Calculated 'R values,' representing ratios of electrophysiologic activity between different electrode areas, as potential diagnostic markers.
Main Results:
- Several 'R values' demonstrated significant separation between CVI patients and control groups, especially in children older than 5 years.
- A low occipital-to-parietal activity ratio was a key indicator in CVI patients.
- The derived 'R values' showed age independence in the normal population and were easily computed.
Conclusions:
- Mathematically derived 'R values' from VEP offer a promising, objective method for confirming CVI diagnoses in children.
- The occipital-to-parietal activity ratio is a particularly sensitive VEP-based parameter for CVI detection.
- These findings suggest 'R values' can serve as valuable confirmatory diagnostic measures for pediatric CVI.
Abstract:
Children with cortical visual impairment (CVI) usually have a typical clinical presentation. However, in some cases, it may be useful to have confirmatory evidence based on objective electrophysiologic information. To achieve this, we examined some mathematically derived parameters constructed from 20 channel visual evoked potential (VEP). A group of 30 children diagnosed with CVI by clinical and CT findings was compared to a normal control group of 52 children. Each recorded VEP was mathematically transformed using Hjorth's source derivation, to reduce reference contamination and enhance local features. The area under the response curve, computed for each channel within a fixed time window, was used as a measure of the response activity at that channel. These areas were then used to construct several parameters ("R values") describing ratios of activities between different recording electrode areas. Some of these ratios provided good separation between patient and control groups, especially for children older than 5 years of age; in particular CVI patients were found to have a low occipital-to-parietal activity ratio. This finding, together with the observed age independence of the R values in the normal population, their ease of computation and possible physiological interpretability, suggest that R values could be used as confirmatory diagnostic measures.