NORMATIVE DATA OF PEAK LATENCIES OF N70, N155 WAVES AND INTER-PEAK LATENCY OF PATTERN REVERSAL VISUAL EVOKED POTENTIALS IN CENTRAL INDIAN POPULATION

Kothari, Bokariya, Singh, Narang, Singh
2013 International Journal of Basic and Applied Medical Sciences   unpublished
The aim was to report the normal values of the N70 latency, N155 latency and interpeak latency of Visual evoked potential [VEP] of central Indian population. This study was conducted in the Neurophysiology unit of the Department of Physiology of our institute. The study comprised of pattern reversal visual evoked potential (PRVEP) recordings by an electronic pattern regenerator inbuilt in an Evoked Potential Recorder (RMS EMG EP MARK II) from 200 eyes of 100 carefully screened visually normal,
more » ... d visually normal, healthy middle aged and elderly individuals having age in the range of 40 to 79 years.This was an observational cross-sectional study. The mean age of the subjects was 56.08 ± 10.87 years (minimum age of 40 years and maximum of 79 years). 57.17 ± 10.92 years was the mean age for males and for females it was 54.30 ± 10.62 years. The overall mean interpeak latency in all the 200 subjects was 68.79±9.49 msec, N70 latency was 66.64±5.59 msec and N155 latency was 135.44±8.31 msec. The normative values of N70 latency, N155 latency & interpeak latency of PRVEPs in the normal adults of central India have been reported in the present study. These can be used for evaluation and interpretation of various VEP abnormalities especially the ones encountering extended temporal dispersion. INTRODUCTION Visual evoked potentials provide a sensitive indication of abnormal conduction in the visual pathway. VEP is a useful clinical tool in the diagnosis and documentation of visual impairment in many neurological and ophthalmological disorders. Like any other neurophysiological test, exquisite attention to the technical details, acquisition of reproducible and reliable waveforms, proper interpretation based on laboratory control values and correlation with the clinical picture are essential for optimal utilization of this technique. Every clinical neurophysiology lab need to set up its own normative data for its population required in clinical practice to identify the abnormal subjects. The preferred stimulus for clinical investigation of the visual pathways is a reversal of a high contrast black and white checkerboard pattern, as it tends to evoke larger and clearer responses than other patterns. The standard clinical test involves the recording of the pattern reversal VEPs (PRVEPs). Pattern-reversal VEPs are less variable in waveform and timing than the VEPs elicited by other stimuli (Odom et al., 2010). Normal VEP Waveform The starting point of VEP waveform is stimulus onset. The waveform of a VEP depends upon the temporal frequency of the stimulus. At low temporal frequencies, the waveform consists of a number of discrete deflections and is termed a transient VEP. The transient responses have the advantage of component analysis (Birch and Subramanian, 2012). The usual PRVEP waveform is the initial negative peak (N1 or N70), followed by a large positive peak (P1 or P100) and followed by another negative peak (N2 or N155). Positive wave P100 is shown with downward polarity and the negative waves are shown with upward polarity in the recording.
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