The Effect of Long-term Systemic versus Local Immunosuppression on Electroretinography in Birdshot Chorioretinopathy

Abstract

Purpose : Birdshot chorioretinopathy (BCR) is an autoimmune disease that typically requires treatment with long-term systemic immunomodulation (SI) or local immunosuppression. The most common long-term local treatment for BCR is the 0.59 g intravitreal fluocinolone acetonide implant (IVFAI). It is unknown how different treatments impact retinal function longitudinally as measured by full-field electroretinogram (ffERG). We hypothesize that eyes with BCR receiving SI may have more stable retinal function compared to eyes receiving IVFAI.

Methods : A longitudinal retrospective study was performed on BCR patients from Casey Eye Institute who had 1) clinical visits and ffERG testing between the years 1999 – 2019, 2) received either SI or IVFAI, and 3) had at least two sequential ffERG and clinical encounters with the same treatment modality spanning at least one year of time. The following metrics were evaluated for each eye: amplitude and timing of the components of the ffERG waveforms in response to dim scotopic, bright scotopic, and photopic single flash and 30 Hz flicker. A rate analysis was performed on each parameter with a linear nested mixed-effects model, controlling for inter-eye correlation and multiple comparisons.

Results : Thirteen patients met inclusion criteria. Overall, eyes treated with SI had positive rates of improvement or slower rates of decline in amplitude compared to eyes treated with IVFAI for dim scotopic b-wave (SI +1.03 μV/yr vs. IVFAI -11.61 μV/yr; p=0.034) and bright scotopic b-wave (SI -5.2 μV/yr vs. IVFAI -17.74 μV/yr; p=0.027). Eyes treated with IVFAI had faster rates of improvement in the implicit time than eyes treated with SI for bright scotopic a-wave (IVFAI -0.22 ms/yr vs. SI +0.02 ms/yr; p=0.023) and photopic a-wave (IVFAI -0.26 ms/yr vs. SI -0.02 ms/yr; p=0.0004).

Conclusions : The data supports our hypothesis that long-term treatment with SI was better than IVFAI for stabilizing rod-dependent function in BCR. However, IVFAI was better than SI for improving cone-dependent function. These results suggest that there may be different systemic versus local immune-mediated pathways that underlie retinal dysfunction in BCR. This study also suggests that combined systemic and local treatments for BCR may provide more comprehensive long-term preservation of retinal function.

This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.