The electroretinogram (ERG) is widely used to diagnose various disorders with panretinal dysfunction. Changes in the photopic, rod-isolated, and bright flash scotopic ERG are compared and analyzed to arrive at more specific diagnoses.¹² (See also chapter 49.) Almost uniformly, poor or less than normal responses are used to determine abnormality, and larger-than-normal responses fall into a conceptual category that “bigger is better” and therefore they must be normal. To examine the question of what is really normal, it is essential to establish good normal controls for a laboratory. Standardized testing is essential, such that the electroretinogram methodology tests isolated cone and rod responses as well as both cone and rod responses together. Flicker and dark-adapted red and blue stimuli give added information. The International Society for Clinical Electrophysiology of Vision (ISCEV) ERG standard establishes protocols for achieving reproducible results that are easily interpreted by experienced ophthalmic electrophysiologists. (See the ISCEV Electrophysiologic standard in chapter 20 or at www.iscev.org.)

The concept of what is “normal” may be more difficult to establish than might be expected, since physiologic measurements have innate variability and setting protocols with multiple variables, such as light flashes that are uniform, pupil dilation that is adequate, standard lengths of dark and light adaptation, and accounting for age, gender, and generalized health and eye status, are all confounding factors in assessing “normality.” To establish normal values, most laboratories run tests on a set of subjects who have had normal eye examinations through a standardized protocol, recording the amplitudes and implicit times of the a- and b-waves for each test parameter. (Rod-isolated ERGs have minimal a-waves.)