ION: isolated monophasic optic neuritis, RON: recurrent optic neuritis; severe ON visual acuity of 20/200 or worse in at least 1 eye at the nadir; pediatric cases; #serum from multiple ethnicity of White, Asian, Black, Hispanic, Mestizo, Middle Eastern, and Native Argentinean; ##serum from Austria, Denmark, France, Germany, Italy, and Turkey.