Anna Brouwer

15 General introduction, aims and scope 1 central retina, including the macula. 39 This thesis focusses on the full-field ERG, which is the most commonly used technique. For the rest of this thesis, when ERG is written, the full-field ERG is implied. ERG waves and types of adaptations There are several waves on an ERG curve that can be identified (Figure 2). The first is the negative a-wave. The a-wave represents the depolarization of the photoreceptors after a flash of light has been emitted. The second wave is the (positive) b-wave. This wave is generated by the bipolar and Müller cells. On the rim of the ascending limb of the b-wave a ‘saw-tooth’ pattern can be observed. These are known as the oscillary potentials (OPs). The origin of these OPs remains unclear, some reports state that they reflect the amacrine cells, whereas others state that they are the result of bipolar cell activity. 41 Besides the a-wave and b-wave, the c-wave and d-wave can be recorded as well. These represent the retinal pigment, and theOFF-center bipolar cells respectively. However, to record these waves, a much longer recording time is required. 42,43 Therefore, they are not routinely recorded and are not a subject of this thesis. Lastly, a more recent aspect of the ERG was identified: the photonegative response (PhnR). 44 The PhnR can be observed after the b-wave. It is the negative reflection of the ERG curve which occurs after the positive b-wave. The PhnR reflects ganglion cell function and may be useful for detecting progression of glaucoma. 45 The PhnR is not a subject of this thesis, because its identification is not a part of our local ERG protocol. When the eyes are adapted to light, the ERG response is primariliy cone driven (photopic response). When the eyes are adapted to the dark, the response to dim (weak) flashes is rod driven (scotopic response). As the flashs strengths become stronger (i.e the light flashes become brighter), a combined rod/cone response is recorded (mesopic response). ISCEV standard and extended ISCEV protocols To ensure that the results of electrophysiological research of vision would be better comparable, the International Society for Clinical Electrophysiology of Vision (ISCEV), has created multiple guidelines to record ERGs, as well as other electrophysiological tests. 38–40,46–48 Nowadays, virtually all scientific papers that report ERGs adhere to these standards. Regarding the ERG, the ISCEV standard states the requirements for the equipment, flash strengths, background illumination, and the adaptation times for both