Anna Brouwer

17 General introduction, aims and scope 1 if they are above the 95 th percentile. These one-sides values are probably chosen because most diseases that affect the ERG result in either reduced amplitudes or increased implicit times, or both. Increased amplitudes or reduced implicit times are rarely seen in case of pathology. Interestingly, the ISCEV standard does not describe howmuch ERGparameters need to be changed to be defined as significantly changed, which is necessary for monitoring purposes. 38 Different types of electrodes To record an ERG several electrodes are necessary: a common, or ground electrode, a reference electrode, and an active electrode which may contact the cornea, bulbar Figure 4: Example of ERG curves of a healthy control of the dark adapted and light adapted ERG of the different flash strengths. Recording time of the first seven flash strengths of the dark adapted ERG are 250ms. Those of the other flash strengths are 200ms. The standard ISCEV flash strengths (Dark adaptation: 0.01 (rod response), 3.0 and 10.0 cds/m 2 (combined rod/cone response) Light adaptation: 3.0 cds/m 2 (cone response) and 30 Hz (cone response)) are indicated in bold. Abbreviations: ERG = electroretinogram, cds/m 2 = candela · seconds/squared meters, ms = milliseconds, μV = microvolts, ISCEV = International Society for Clinical Electrophysiology of Vision. 30 Hz 10.0 30.0 3.0 1.0 0.3 0.1 0.03 0.01 0.003 0.0003 0.001 0.0001 0 50 100 150 200 ms 50 µV 0 50 100 150 200 ms 200 µV Darkadapted Light adapted Flashstrength incds/m 2 10.0 3.0 1.0 0.3 Flashstrength incds/m 2 250 b b b b a a a a trough peak a a a a a a a a a b b b b b b b b b b b b