[Skin electrodes for electroretinography in unsedated children]

Contact lens electrode ERG is not well tolerated by children. So far, skin electrode ERG has suffered from a weakly defined geometrical relationship to the sources of ERG potentials. Because of the cuplike electric ocular field distribution, skin electrodes were placed: (1) in the middle of the lower eyelid (in order to be positioned in close proximity to the anterior apex of the cornea, which belongs to the electropositive inner surface of the cup); (2) 20 mm laterally to the temporal canthus (in proximity to the cup's electronegative outer surface). (3) Grounding was achieved by attaching a third skin electrode in the forehead midline. Instead of complete dark adaptation, adaptive illumination of 0.1 cd.m-2 was used to avoid frightening the children. After 10 min of adaptation, the examination started. Feeling safe on mother's lap, the little patient looked into a frosted glass screen (about 75 degrees of visual angle, depicting Mickey Mouse) on which a series of strobe flashes was delivered along the lines of the ISCEV ERG Standard: (1) blue flashes: filter no. 625 (Röhm and Haas); repetition rate 0.1 Hz; stimulus strength of white flashes 1.5 cd.m-2 s; (2) red flashes: filter no. S502 (Röhm and Haas); repetition rate 1 Hz; stimulus strength of white flashes 21.75 cd.m-2.s; (3) weak white flashes: stimulus strength 1.5 cd.m-2.s; repetition rate 0.3 Hz; (4) strong white flashes: stimulus strength 11.25 cd.m-2.s; repetition rate 0.3 Hz; (5) white flicker flashes: stimulus strength 1.5 cd.m-2.s; frequency 10, 30, 60 Hz. Recording of single stimulus responses turned out to be feasible; however, to achieve the best results, between 8 and 32 ERG responses were averaged. To illustrate the benefits of skin electrode ERGs in practice, the results of some cases are presented and discussed with respect to clinical findings.