title: Visual Evoked Potentials: Normative Values and Gender Differences.
abstract: BACKGROUND
  Visual evoked potentials (VEP) are used to assess the visual pathways through the optic nerves and brain. A normal VEP response to a pattern-reversal stimulus is a positive mid occipital peak that occurs at a mean latency of 100 ms. VEP may be affected by variety of physiological factors including age, sex, visual acuity and pupillary size.
  
  
  OBJECTIVE
  The present study was performed on healthy medical students to determine the normative values and to investigate the effect of sex and anthropometric parameters on visual evoked potentials.
  
  
  METHODS
  The study was conducted on 100 healthy medical students of Government Medical College, Patiala in the age group of 17-20 years, in which there were 50 males and 50 females. The anthropometric parameters including age, height, weight, BMI, BSA and Head circumference were recorded in all the subjects. VEP was recorded with a PC based, 2 channel, RMS EMG EP mark II machine and standard silver-silver chloride disc electrodes. A VEP monitor displaying checker board was used to give the pattern reversal stimulus. The VEP parameters recorded were latencies to N70, P100 and N155 waves, and peak to peak amplitude of P100 wave.
  
  
  RESULTS
  Our results showed that the latencies of N70, P100 and N155 waves were significantly longer in males as compared to females. The amplitude of P100 wave was higher in females in both left and right eye as compared to males. No significant correlation was found between VEP parameters and head circumference in both male and female subjects in our study.
  
  
  CONCLUSIONS
  Gender is an important variable affecting the VEP. The exact reason of gender difference is not clear, but it may be related to anatomical or endocrinal differences in the two sexes.
authors.affiliation: Assistant Professor, Department of Physiology, Gian Sagar Medical College And Hospital , Banur, Patiala, India .
authors.forename: Ruby
authors.initials: R
authors.lastname: Sharma
authors.affiliation: Assistant Professor, Department of Medicine, Gian Sagar Medical College And Hospital , Banur, Patiala, India .
authors.forename: Sandeep
authors.initials: S
authors.lastname: Joshi
authors.affiliation: Professor and Head, Department of Physiology, Government Medical College , Patiala, India .
authors.forename: K D
authors.initials: KD
authors.lastname: Singh
authors.affiliation: Professor, Department of Physiology, Government Medical College , Patiala, India .
authors.forename: Avnish
authors.initials: A
authors.lastname: Kumar
keywords: Amplitude; P100 Latency; Pattern Reversal; Visual Pathway