Higher macular volume in patients with MS receiving fingolimod: positive outcome or side effect?

In the evaluation of patients with multiple sclerosis (MS), optical coherence tomography (OCT) is gaining traction as a tool to assess thinning of the retinal nerve fiber layer (RNFL) and, more recently, for looking at total macular volume (TMV) thickness, with both measures used as potential biomarkers for progression of disease. In medicine, it is not uncommon for structural changes to be presumed to reflect a certain physiologic process, when in fact, an alternative mechanism is at play. Fingolimod (FTY-720) is a sphingosine-1-phosphate receptor modulator that is an approved oral treatment for MS and leads to reduced cortical volume loss in patients with MS.(1) Similar to other disease-modifying agents, it is likely to be judged in part by its ability to slow loss of the RNFL and TMV. But would such a judgment be valid?