Optical coherence tomography (OCT) is a non-invasive imaging technique that allows the different layers of the retina to be visualised in vivo. One of them is the so-called retinal nervous fibre layer (RNFL), which is made up of amyelinic axons from the ganglionic cells, and therefore part of the central nervous system. Recent studies have begun to examine possible applications of OCT in the field of neurology and, more specifically, the usefulness of measuring the thickness of the RNFL in multiple sclerosis (MS). In both cross-sectional and longitudinal studies it has been shown that a decrease in the RNFL is produced in eyes that are affected and unaffected by optic neuritis in MS patients, compared with controls. Several studies have found evidence of an inverse relation between the thickness of the nerve fibre layer and the neurological disability or cerebral atrophy parameters in magnetic resonance imaging of the brain in these same patients. The correlations are, however, weak and sometimes contradictory. Although there are still many doubts that need settling, the role OCT may play in gaining a better understanding of the disease and its follow-up and monitoring seems promising. A review of the different studies published on the thickness of the RNFL in patients with MS will also be conducted.