In MS, early work has suggested certain retinal measures, particularly the width of the layer that consists largely of retinal ganglion cell nerve axons, as candidate biomarkers, under the hypothesis that neuroretinal tissue reflects global central nervous system (CNS) pathology. Conceptually, this would seem reasonable, given the frequency for anterior visual pathway involvement as the primary presentation of MS; and in addition, the unmyelinated ganglion cell axons that form the retinal nerve fibre layer (RNFL) are a direct extension of the brain, and global neurodegeneration would be expected to involve these neurones - particularly in MS, where the disease lesions have a predilection for the periventricular regions, which are in close proximity to the optic radiations.