 The primary objective of the study is to assess full-field visual evoked potential FF-VEP latency in subjects who were enrolled in Study 215ON201 NCT01721161 2 years 4 months after the last study visit. The secondary objective is to assess clinical progression and severity of central nervous system CNS demyelinating disease in subjects who were enrolled in Study 215ON201 2 years 4 months after the last study visit. No study drug dosing is planned for this study. 