GFAP and sarcoidosis: We particularly encourage clinicians to look for accompanying symptoms and signs that could guide the diagnosis, such as bilateral optic disc edema for GFAP-antibody associated ON, concomitant retinitis, vitreal inflammation and a lack of MRI findings in CRMP5-IgG ON, the dramatic response and dependency on steroid treatment for CRION, the associated uveitis and anterior chamber inflammation for sarcoidosis-related ON, or the prominent pain and central vision sparing of OPN.