This research sub-study is being completed as a part of the Multicenter, Randomized, Double-Blind, Parallel-Group, Placebo-Controlled Study to Evaluate the Efficacy and Safety of PEGylated Interferon Beta-1a (BIIB017) in Subjects with Relapsing Multiple Sclerosis (Protocol #: NA_00028117). This substudy is being done to understand the efficacy of BIIB017 by measuring the nerve fiber thickness in the eye.