A New Contact Lens Electrode

Abstract

A new kind of contact lens electrode is described which has superior electrical characteristics to the traditional type and overcomes many of its disadvantages. In addition it can permit unimpaired vision by the subject for the simultaneous recording of ERG and pattern VER

Of all electrophysiological signals the electroretinogram (ERG) provides the investigator with a site which is at once the best and the worst for recording. No other signal can be recorded from the surface with such a direct electrical pathway to its source; no other surface electrode site is as sensitive as the cornea. Hence, although the ERG can be recorded using skin electrodes, some means of making electrical contact with the cornea is invariably used. Fundamentally, the method of making this contact has not changed since it was described by De war (1877). Isotonic saline solution is held in contact with the cornea by means of a container of some kind and this also supports an electrode (generally metallic) with its end in the saline. The design of the saline container has been greatly improved since Dewar used a ring of clay and Hartline (1925) used goggles. The major step forward was the introduction of the contact glass electrode independently by Riggs (1941) and Karpe (1945). Electrodes of this type, including the many variations subsequently introduced by other workers, are commonly in use today. The contact glass is made of moulded plastic and the most favoured material for the electrode is silver, although stainless steel and, occasionally, gold or platinum are used. The main disadvantages of the contact glass electrode are discomfort, difficulty in avoiding air bubbles, which spoil the electrical contact, and difficulty in fitting. On the other hand they can be fenestrated if clear vision is required (Jacobson et al. 1958) and the photovoltaic artefact may generally be avoided by the use of sufficient black paint (Best, 1953).