Standardized visual evoked potentials for telematic electrodiagnosis from five laboratories in three European countries

The pattern-reversal visual evoked potential (PR VEP) is an electrodiagnost ic test which uses an alternating checkerboard pattern as the visual stimul us. To validate the performance of an automated testing system, the equipme nt was installed in five locations in three countries (the UK, Greece and C yprus). PR VEPs require accurate control of stimulus size, luminance, contr ast, timing, multichannel recordings and various modes of signal processing . Recordings were obtained from 70 subjects, 18-34 years old (seven male an d seven female in each laboratory). The data were transmitted by telephone line to the central station in Bristol. Only in Bristol were the operators experienced. There were no significant differences between laboratories in latency or amplitude of the N70 and P100 components. There were no signific ant differences between eyes. There were significant differences between th e sexes but this was related to head size. Decreased square size used in st imulation produced an increased latency in both components. The amplitude o f the N70 component increased while that of the P100 decreased with reduced square size. The results confirmed the ability of the automated system to produce standardized PR VEP recordings comparable to those obtainable in ad vanced laboratories. The system performed well in different locations using inexperienced operators. The system is suitable for multicentre research s tudies and telemedicine.