Anna Brouwer

19 General introduction, aims and scope 1 Other factors can influence the recorded response, but are more difficult to address, include: DTL position, media opacities, age and even the time of day. 59–64 Uveitis can cause several types of media opacities, including corneal keratopathy, cataracts, flare, cells in the anterior chamber, vitreous cells, and vitreous haze. 1,29 These can all reduce the amount of light which reaches the retina. Posterior synechea, which can prevent the pupil form reaching full mydriasis can have a similar effect. 43 However, these media opacities will often only slighty reduce the amount of light that reaches the retina, but they will all have a larger effect on light scattering. Therefore, they will have a much larger influence on the mfERG than the ffERG. However, they can all have an effect on the ERG. Therefore, media opacities are always taken into consideration in the different chapters of this thesis. Literature about electroretinography of uveitis The role of the ERG is unclear for most forms of uveitis but the ERG may be used for monitoring birdshot uveitis, because some studies indicate that the 30 Hz flicker response of the ERG is a very sensitive marker to determine if systemic medication may be tapered. 65,66 Also, there are some reports that state that the ERG is useful to determine the activity of the inflammation in birdshot. 66 The ERG abnormalities in birdshot uveitis may improve after the inflammation has become inactive, but there are also reports that the ERG changes may be permanent. 65,67–72 There are indications that the ERG is helpful in predicting visual outcome in birdshot, but not all studies found a significant association. 71,72 However, all studies that investigate the ERG in uveitis were conducted with relative small sample sizes and often a comparison with other diagnostic tests was not made. This makes it difficult to assess the true value of the ERG in uveitis. Therefore, the ERG is not a part in the standard diagnostic work-up in the University Medical Center Utrecht. Also, the ERG is not always correlated to other tests that monitor disease activity, and its measurement takes up a long period of time. Lastly, the true value of the ERG for monitoring is not elucidated. 69,73 However, ERG changes in uveitis are not restricted to birdshot uveitis. There are many reports of ERG changes in different forms of uveitis. 74 Table 1 gives an overview of the different types of ERG and mfERG abnormalities that are described in uveitis. Many of these studies are case series, or studies conducted with small sample sizes. Depite the many reports of ERG abnormalities in uveitis, and the few reports that the ERG may be usefull for monitoring or prognosis, to our knowledge the ERG is not routinely used to monitor these uveitis entities.