Bilateral retrobulbar optic neuritis combined with optic perineuritis associated with atezolizumab treatment for small cell lung carcinoma.

Retrobulbar ON and OPN associated with atezolizumab are rare side effects that are easily overlooked. Immune-related ON has unique features and requires early identification. The primary treatment for optic nerve irAEs is corticosteroids, but this is not standardized and should be used with caution.