75 Original Article Nepal Med Coll J 2012; 14(2): 75-79 Effect of head circumference on parameters of pattern r eversal Visual evoked potential in healthy adults of central India R Kothari, 1 R Singh, 1 S Singh 2 and P Bokariya 3 1 Department of Physiology, 2 Department of Ophthalmology, 3 Department of Anatomy, MGIMS, Sevagram, Maharashtra, India Corresponding author: Ramji Singh, Professor and Head, Department of Physiology, MGIMS, Sevagram, Maharashtra, India; e-mail: sramji57@gmail.com ABSTRACT Visual evoked response testing has been one of the most exciting clinical tools to be developed from neurophysiologic research in recent years and has provided us with an objective method of identifying abnormalities of the afferent visual pathways. Investigation were carried out to see whether the head circumference influence the pattern reversal visual evoked potential (PRVEP) parameters. The study comprised of pattern reversal visual evoked potential (PRVEP) recordings in 400 eyes of 200 normal subjects. Two hundred fourty eight eyes were males and 152 eyes were from 76 female subjects recruited from the Central Indian population in the age range of 40-79 years. Visual evoked potential (VEP) recordings were performed in accordance to the standardized methodology of International Federation of Clinical Neurophysiology (IFCN) Committee Recommendations and International Society for Clinical Electrophysiology of Vision (ISCEV) Guidelines and montages were kept as per 10-20 International System of EEG Electrode placements. The stimulus configuration in this study consisted of the transient pattern reversal method in which a black and white checker board was generated (full field) and displayed on a VEP Monitor by an electronic pattern regenerator inbuilt in an Evoked Potential Recorder (RMS EMG EP MARK II). VEP latencies, duration and amplitude were measured in all subjects and the data were analyzed. The correlation of all the electrophysiological parameters with head circumference was evaluated by Pearson’s correlation co-efficient (r) and its statistical significance was evaluated. The prediction equations for all the VEP parameters with respect to head circumference were derived. We found a positive correlation of P 100 latency and N 155 latency with mean head circumference, while a highly significant negative correlation were noted of P 100 amplitude with head circumference. N 70 latency was significantly correlated with head circumference. P 100 duration showed in negative correlation with head circumference. These findings suggest that VEP latencies, duration and amplitude are influenced by the head circumference of the individual in a sample of healthy subjects and head circumference can be a useful predictor of VEP peak latencies, amplitude and duration. Keywords: Pattern reversal, P100 latency, P100 amplitude, P100 duration, N70 Latency, N155 latency. INTRODUCTION Visual evoked potential (VEP) is a graphic illustration of the cerebral electrical potentials generated by the occipital cortex evoked by a defined visual stimulus. 1 Transient Pattern Reversal Visual Evoked Potential generated in the cortical and sub-cortical visual areas when the retina is stimulated with pattern light is a very important non- invasive low-cost method and highly objective tool in detecting abnormalities of visual system. The normal VEP indicates the intactness of the visual system. 2 A number of factors that influence VEP waveform include the age, gender, height and head circumference of the subject but it is observed that there is not much data available in literature regarding changes in the visual evoked responses with all these parameters especially in this part of the world. Therefore an attempt was made by us to study the influence and correlation of head circumference with VEP in healthy adults of Central India. The aim was to record the VEP waveform and evaluate its parameters in healthy males and females having normal visual acuity in the age group of 40-79 years. MATERIALS AND METHODS A total of 200 control subjects were included in this study. Out of these, 124 (62%) were males and 76 (38%) were females. The mean age for males was 57.17 ± 10.92 years (range from 40-79 years) Similarly, for females the mean age was 54.30 ± 10.62 years (minimum age of 40 years and maximum of 79 years). Approval from the Institutional Ethics committee was obtained for the study. Written Informed consent were also taken from the volunteers before the study after explaining the details of the investigation. Detailed systemic and thorough ophthalmological Original Article Nepal Med Coll J 2012; 14(2): 75-79