Electrodiagnostic Tests in Eye Disease.

Basis of the Electroretinogram An electrical potential exists between the cornea and the fundus of the living eye. When the eye is illuminated by a flash of light a small potential is generated in addition to this corneofundal potential, which forms the ERG. This is analogous to the way in which the ECG is recorded above the steady skin potential. The final response is the sum of a number of components arising in the different neural layers of the retina and consists primarily of an initial negative a-wave, followed by a positive b-wave. A contact lens electrode and an indifferent electrode placed on the skin near the eye record the ERG. Diseases which affect the receptor cells or the second order neurones, the bipolar cells, will alter the size and shape of the ERG, (Jacobson, 1961).