January 1995
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86 Reads
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55 Citations
As early as 1865, Holmgren found that a light stimulus could cause a change in the electrical potential of the amphibian eye. Shortly afterwards, similar findings were reported by Dewar from Scotland. He showed that light illumination through the pupil, which had previously been covered, caused a slight movement of a galvanometer, suggestive of a positive electrical change in the cornea relative to the back of the eye (1). This light-induced electrical activity of the eye was called the electroretinogram. Now, the electroretinogram response is commonly abbreviated to the ERG. Gotch (2) was the first to report that the response of the eye to a light flash consisted of two waves; first the cornea became negative and then a positive wave of larger amplitude appeared. Later, Einthoven and Jolly (3) separated the ERG response into three waves. The first wave to appear immediately after turning on a light stimulus was negative on the cornea. It was followed by a positive wave and a final slower wave that was also positive. Einthoven and Jolly (3) suggested that the light stimulus triggered a chain of reactions leading to the formation of products A, B, and C, and that every electrical wave indicated a change in a "relevant" product. These authors' work was the foundation for the form of analysis of the ERG used to the present day. The waves are called a-, b- and c-waves. An additional corneal-positive wave, that is more rarely recorded at the termination of the light flash, is called the d-wave.