EXTENDED REPORT Electrophysiological characterisation and monitoring in the management of birdshot chorioretinopathy

Aims: To characterise patients with birdshot chorioretinopathy (BCR) clinically and electrophysiologically in order to monitor changes in retinal function before and after treatment with corticosteroids and/or immunosuppression. Methods: 18 patients with BCR were characterised clinically and electrophysiologically. Serial studies were performed on 14 patients in order to monitor changes in retinal function before and after treatment with corticosteroids and/or immunosuppression. Results: Most patients presented with characteristic subretinal pale spots, were HLA-A29 positive, and had diverse signs of ocular inflammation. Various electrophysiological abnormalities were present. Moderately severe bilateral pattern electroretinogram (PERG) abnormalities at presentation were common, reflecting macular dysfunction. Cone mediated 30 Hz flicker electroretinograms (ERGs) were consistently delayed before treatment, and were the most sensitive parameter of retinal dysfunction. Scotopic maximal ERG responses were abnormal in 13 patients; 10 had an electronegative maximal ERG or a reduced b:a ratio in one or both eyes. Single flash photopic ERGs were less often and less severely affected. Photopic ON and OFF ERG responses often revealed predominant ON response b-wave abnormalities with relative OFF response preservation. ERGs improved in treated cases, sometimes preceding clinical signs of recovery. Pattern ERG improvements occurred, possibly reflecting the resolution of macular oedema. Conclusions: The ERG data confirm that BCR frequently affects inner retinal function of cone and rod systems. Clinical features were not reliable indicators of functional deterioration or recovery. Objective electrophysiological assessment of retinal function demonstrated improvement following treatment and provides a reliable method of monitoring treatment efficacy, enabling management decisions to be taken with greater confidence and allowing early initiation or modification of treatment.