The effect of head size on visual evoked potential in healthy adults of north india.

Abstract

Aim: Visual Evoked Potentials (VEPs) result from change of brain activity following application of intermittent visual stimulus to the visual system. They provide a quantitative measure of the functional integrity of the visual pathways. The function measured includes that of the optic nerve, through the optic chiasma and tract, to the lateral geniculate bodies and the geniculocalcarine projection to the visual cortex. A number of factors influence VEP waveform and include age, gender, and height and head circumference of the subject. Head size is an important factor which influences VEP values. The present study was undertaken to study the influence and correlation of head circumference with VEP in adult healthy males and females of our region. Method: The study comprised of 103 healthy subjects between the age group of 20-50 years consisting of both males and females. Visual Evoked Potential was recorded using pattern reversal stimulation using standardized methodology in accordance with International Federation of Clinical Neurophysiology (IFCN). Results: Correlation of Head size with various parameters of VEP was done using Pearson’s correlation co-efficient (r). With increase in head size the P-100 Latency showed progressive increase. The correlation between P-100 Latency and Head Size was found to be positive and was very significant (p<0.001). The N-145 and N-75 latencies also showed positive correlation with increasing head size. The P-100 Amplitude showed a non-significant decrease with increasing Head Size. Conclusion: Our study demonstrates that head size has definite and significant Influence on various Visual Evoked Potential Parameters. Using the same reference data in patients with different head size may result in erroneous reporting; thus head size should be considered for VEP normative studies and reference data derived accordingly for clinical purpose so as to differentiate between normal and abnormal cases.