Anna Brouwer

3 81 ERG abnormalities in non-infectious uveitis often persist Apart from the severity of inflammation, eyes with an improved ERG had more frequently media opacities or a small pupil size during their first ERG. In the light- adapted ERG implicit times increase when the intensity of the flash strength becomes stronger. Media opacities or a small pupil size can reduce the retinal illuminance of the stimulus flash leading to changes in b-wave implicit time of non-pathologic origin. 4,12 Therefore, it is possible that the improved implicit time of the cone b-wave may even be underestimated due to the improvement of media opacities. Effects of changes in pupil size were addressed by excluding eyes with a pupil size difference > 1 mm. Because the implicit time of the cone b-wave in uveitis over time has not previously been studied, it is not possible tomake comparisons with literature. However, there are some reports of follow-up ERG’s in birdshot uveitis that show that the 30 Hz flicker response can improve after systemic treatment with corticosteroids, but not in all cases. 5 Furthermore, other ERG parameters than the 30 Hz flicker response can be permanently affected in birdshot uveitis. 16,17 In the current study, we could only replicate that the 30 Hz flicker response improved in the minority of the birdshot patients after the start of systemic treatment, possibly because 6 out of 7 of the included birdshot patients already used systemic medication at the time of the first ERG. In these patients the implicit time of the 30 Hz flicker response did improve in 4 out of 14 eyes, whereas the implicit time of the cone b-wave did not improve. Some studies state that a change of > 30% in amplitude is necessary to define improvement or deterioration, based on Berson’s study on decline in retinitis pigmentosa (RP). 18 However, the ERG in RP is generally much more severely affected than in uveitis, where the amplitude often does not change significantly. Most studies that report on follow-up results of the ERG in uveitis, do not specify how improvement is defined, 5,7–10 for instance, which aspect of the ERG changed during follow-up. In our study we observed that the different parameters of the ERG may behave quite differently. For uveitis monitoring, we found that the implicit time of the cone b-wave is the most sensitive parameter. In summary, this study demonstrates that a prolonged implicit time of the cone b-wave often persists in uveitis. In a minority of cases, this loss of retinal function can improve if the inflammation becomes less active. This emphasizes the importance to treat the inflammation adequately and early in uveitis. Further research is needed to investigate to which extent the implicit time of the cone b-wave can be used as a prognostic marker in uveitis.