Electroretinography of disease activity and treatment response in birdshot chorioretinopathy

To identify full-field electroretinographic (ffERG) biomarkers that differentiate active versus inactive birdshot chorioretinopathy (BSCR) and long-term efficacy of intravitreal versus systemic immunosuppression.

Patients with BSCR at Casey Eye Institute with ffERG between 1999-2019 were included (n = 29). A group of healthy patients was used as controls (n = 47). Patients with BSCR were categorized as active or inactive based on the uveitis specialist's clinical assessment. Cross-sectional comparison of ffERG markers between active, inactive, and control patients was performed, in addition to rate analysis of ffERG metrics in BSCR eyes treated with either intravitreal fluocinolone acetonide 0.59 mg (IVFAI) or systemic immunomodulation (SI).

Both active and inactive BSCR tended to have lower amplitude and slower timing than controls, but only 30 Hz flicker time (p < 0.001, p < 0.01) and dim scotopic b-wave amplitude (p < 0.001, p < 0.05) were significant. Timing for inactive BSCR was faster than active for bright scotopic a-wave (p < 0.01), photopic b-wave (p < 0.01), and 30 Hz flicker (p < 0.01). Eyes treated with SI showed improvement in dim scotopic b-wave amplitude compared to a decline for IVFAI (p < 0.05), whereas eyes treated with SI showed slower degradation of bright scotopic b-wave amplitude (p < 0.01). Conversely, eyes treated with IVFAI showed greater improvement in bright scotopic (p < 0.05) and photopic a-wave timing (p < 0.01).

Timing of 30 Hz flicker, bright scotopic a-wave, and photopic b-wave may be useful biomarkers for disease activity in BSCR. Moreover, both SI and IVFAI were effective in preserving retinal function to varying degrees.