ORIGINAL RESEARCH ARTICLE Comparison of cathode ray tube and liquid crystal display stimulators for use in multifocal VEP Mary¨ke Fox • Colin Barber • David Keating • Alan Perkins Received: 18 September 2013 / Accepted: 18 June 2014 / Published online: 2 July 2014 Ó Springer-Verlag Berlin Heidelberg 2014 Abstract Purpose To compare the modified signal-to-noise ratio (SNR*) of multifocal visual evoked potential (mfVEP) responses elicited by a cathode ray tube (CRT) and liquid crystal display (LCD) monitor in normal subjects. Methods An LCD monitor and CRT monitor were luminance and contrast matched. Luminance stability and the effect of viewing angle on luminance and contrast was measured for both screens. The SNR* of mfVEP responses from 15 normal subjects was compared between the stimulators using repeated measures analysis of variance. Results The CRT monitor took 10 min from switch on to reach the desired luminance compared to 60 min for the LCD monitor. LCD luminance was sensitive to variations in ambient temperature, fluctuating by 10 cd/m -2 over approximately 20–27 °C, whereas CRT luminance was stable. Luminance variation from the centre to the edge of the CRT screen was 8 % when viewed perpendicularly and 28 % when viewed at an angle of 25°, compared to 24 and 46 %, respectively, for the LCD screen. Contrast was[94 % and varied by \3 % across both monitors for both viewing condi- tions. There was no significant difference in SNR* between responses elicited by the two stimulators (p = 0.76). Conclusions CRT and LCD stimulators elicited mfVEP responses with similar SNR* in normal subjects. This study highlighted practical issues with the use of LCD monitors as visual stimulators, particularly with regard to warm-up time, luminance stability and luminance uniformity. Keywords CRT  LCD  Electrophysiology  Multifocal  Visual evoked potential Introduction Visual evoked potential (VEP) stimuli have tradition- ally been presented on cathode ray tube (CRT) monitors, but these have now been superseded by liquid crystal display (LCD) monitors and are no longer produced. The crucial difference between LCD and CRT monitors is in the way the pixels emit light: a CRT monitor generates a bright pulse of light of around 2 ms duration at the start of each frame, whereas an LCD monitor generates a lower constant M. Fox (&)  C. Barber  A. Perkins Nottingham University Hospitals NHS Trust, Derby Road, Nottingham NG7 2UH, UK e-mail: marykef@yahoo.com D. Keating Tennent Institute of Ophthalmology, Gartnavel General Hospital, 1053 Great Western Road, Glasgow G12 0YN, UK A. Perkins Radiological and Imaging Sciences, School of Medicine, University of Nottingham, Derby Road, Nottingham NG7 2UH, UK 123 Doc Ophthalmol (2014) 129:115–122 DOI 10.1007/s10633-014-9451-0