Skin ERGs: their effectiveness in paediatric visual assessment, confounding factors, and comparison with ERGs recorded using various types of corneal electrode.

Comparison of scotopic and photopic ERGs recorded using a variety of ERG electrodes show that contact lens electrodes produce the largest ERGs, and these are about 30-50% larger compared with those recorded with foil or thread electrodes, which contact a smaller part of the cornea. Flash ERGs recorded from infra-orbital skin electrodes are about one eighth the size of those recorded with contact lens electrodes, and around one quarter the size of those recorded with foil or fibre corneal electrodes. Reliable ERGs can be obtained in young children from infra-orbital electrodes sited centrally, within 1 cm of the rim of the eyelid, when signal averaging is used. Stimulation under fully darkened laboratory conditions with red and dim blue flashes permit assessment of cone and rod function, respectively. Factors such the recording electrode position, electrode derivation, upward rotation of the eye, eyelid closure and markedly constricted pupils can degrade the skin ERG. There are strong diagnostic advantages in recording the VEP concurrently with the skin ERG, particularly in young children. Examples of recordings in Leber's amaurosis, delayed visual maturation, albinism, optic nerve hypoplasia, achromatopsia add X-linked congenital stationary nightblindness are shown to demonstrate how ERG/VEP recordings can help in distinguishing between these conditions.