Anna Brouwer

16 Chapter 1 dark adaptation (DA) and light adaptation (LA). The guidelines are updated regularly and with each update the writers try to ensure that this is done in such a manner that research can still be compared, even when a previous ISCEV version was adhered to. This implies that flash strengths are added, but not removed. 49 Besides the ‘basic’ ISCEV standards, which state the minimum requirements for an ERG (DA 0.01 (rod response), DA 3.0 and 10.0 cds/m 2 (combined rod/cone response), LA 3.0 cds/m 2 (cone response) and 30 Hz (cone response)), ISCEV has also created multiple extended protocols. These extended protocols are mostly used in a scientific setting. However, in several Dutch hospitals, including the University Medical Center Utrecht (UMCU) and Bartiméus diagnostic Centre for complex visual disorders in Zeist, an extended protocol is recorded as standard practice. Recently new extended protocols were published. Many of the flash strengths of the extended protocol that was used in this thesis overlap with these new extended protocols, but not all. 50,51 Figure 4 shows an example of ERG curves of a healthy control of the extended protocol that was used in this thesis. The ISCEV standards also describe how reference values should be obtained. It is important to have local reference values, because the type of equipment, type of electrodes, and local protocols can all influence the recorded ERG responses. Regarding amplitudes, the ISCEV standard states that amplitudes below the 5 th percentile should be considered abnormal. Implicit times are considered abnormal b-wave ms µV RPE Bipolar cell b-wave Photoreceptor a-wave Müller cell b-wave Ganglion cell PhnR Horizontal cell Amacrine cell OPs Choroid RNFL amplitude b-wave implicit time a-wave amplitude a-wave implicit time b-wave light ash a-wave PhnR OP Figure 3: Explanation of ERG curves in relation to retinal cells. Abbreviations: ERG = electroretinogram, ms = miliseconds, μV = microvolt, OP = ocillary potential, PhnR = photonegative response, RNFL = retinal nerve fibre layer, RPE = retinal pigment epithelium.