VEP Measurement and Reporting

Normal values. Although standardization should ensure similar VEP waveforms across laboratories, each laboratory must establish its own normative values using its own stimulus and recording parameters. The construction of a normal sample for laboratory norms should include the factors of age, sex, and interocular asymmetry. Adult normative data cannot be generalized to pediatric or elderly populations. Interocular comparison of amplitude and of peak time increases the sensitivity of the VEP to monocular conditions. Laboratory normal ranges should use descriptive statistics that do not assume a normal distribution, but are based on the calculation of the median and percentiles from the observed sample distribution. We recommend the 95% reference interval as the minimum limit of normal (i.e. the range from 2.5% to 97.5%).

VEP reporting.
A minimum of two recordings of each VEP condition should be acquired, measured and displayed to confirm reproducibility of the data. Reports using the standard VEP protocols should specify the following stimulus parameters; the field size of the stimulus, the strength (time integrated luminance) of the flash or mean luminance of the pattern, the pattern element sizes and the contrast of pattern stimuli, the frequency of stimulation, and the eye tested. In addition the following recording parameters should be reported; the filter settings and the locations of the positive (i.e., active) and negative (i.e., reference) and indifferent (i.e., ground) electrodes.

Traces should have a clear indication of polarity, time in milliseconds, and amplitude in microvolts. We recommend that VEP traces be presented as positive upwards. All VEP reports, including those for non-standard responses (whether for local records or for publication), must report the peak time and amplitude measurements along with the normal values and the limits of normal. Report should indicate whether the recordings meet this ISCEV standard.

VEP interpretation.
VEP abnormalities are not specific and can occur in a wide variety of ophthalmological and neurological conditions. The interpretation should include statements about the normality and abnormality of the result in relation to normative data as well as comparison between the eyes or with previous records. The type of abnormality in the VEP should be described and this should be related to the clinical picture and to other visual electrodiagnostic results.