Anna Brouwer

Chapter 3 72 We included 72 patients (114 uveitis eyes) for this follow-up study. Of the initial 80 patients who had an ERG in the first year of onset of uveitis, four no longer wanted to participate, three were referred back to another hospital and one moved to another country. All patients were ≥ 18 years of age, mentally competent, and gave informed consent to participate. Patients were seen at the University Medical Centre Utrecht, a tertiary referral centre for uveitis. Patients with juvenile idiopathic arthritis, diabetic retinopathy, retinal dystrophy, family history of retinal dystrophy, myopic degeneration, or severemedia opacities were excluded. Ethical approval was requested and obtained from the Medical Ethical Research Committee of the University Medical Centre Utrecht. This study was conducted in compliance with the ethical principles of the Declaration of Helsinki. ERG analysis Electroretinograms were performed on the same day as an outpatient clinic visit when uveitis activity was assessed. Electroretinograms were measured according to an extended protocol, with more flash strengths than the standard International Society for Clinical Electrophysiology of Vision (ISCEV) protocol. 11 The flash strengths increase with approximately 0.5 log units steps and range from 0.0001 to 30.0 cds/m 2 (12 flash strengths) for the dark-adapted ERG (DA) and from 0.3 to10.0 cds/m 2 (4 flash strengths) for the light-adapted ERG (LA) and include a 30 Hz flicker response as well. We used Dawson-Trick-Litzkow (DTL) electrodes as active electrodes, and an Espion E3 system with ColorDome stimulator (Diagnosys LLC, Cambridge, UK) for flash stimulation. Full details of the ERG measurement procedure, as well as our reference values, were previously described. 4 In this study we focus on changes in the implicit time of the cone b-wave, but other aspects of the ERG were investigated as well. The implicit time of the cone b-wave is correlated to the peak implicit time of the 30 Hz flicker response (Spearman’s rho coefficient 0.620 - 0.814 p < .001). 4 Because the prolonged cone b-wave was the most frequent and characteristic ERG abnormality in uveitis that we observed in our previous study, we focused on differences in the cone b-wave To our knowledge there are no internationally accepted criteria to define whether an ERG has improved or worsened, but only criteria to describe whether an ERG is normal or abnormal (in- or outside reference values). In this study we used the difference inmilliseconds (ms) of the implicit time of the cone b-wave of first ERGminus the follow-up ERG to define whether the ERG was stable, improved or worsened. Because pupil size affects the implicit time of the cone b wave, we excluded eyes with a pupil size difference > 1 mm between the first and follow-up ERG.