The visual pathway as a model to understand brain damage in multiple sclerosis.

Patients with multiple sclerosis (MS) almost always experience effects in the visual pathway; and thus, visual dysfunction is not only common but also highly relevant. The visual pathway represents a model of acute focal central nervous system (CNS) damage, through acute optic neuritis and retinal periphlebitis, as well as a model of chronic, diffuse CNS damage through chronic retinopathy and optic neuropathy. The optic pathway can be accurately evaluated in detail, due to the availability of highly sensitive imaging techniques (e.g. magnetic resonance imaging or optical coherent tomography) or electrophysiological tests (multifocal visual evoked potentials or electroretinography). These techniques allow the interactions between the different processes at play to be evaluated, such as inflammation, demyelination, axonal damage and neurodegeneration. Moreover, these features mean that the visual pathway can be used as a model to test new neuroprotective or regenerative therapies.

Is the incidence of optic neuritis rising? Evidence from an epidemiological study in Barcelona (Spain), 2008-2012.

It is currently believed that the incidence rate of optic neuritis (ON) ranges between 0.56 and 5.1 cases per 100,000 person-years. However, since these figures were generated, they have not been updated and there are suggestions that the incidence of ON is on the rise. When designing new therapies and clinical trials for ON, and to improve the management this disease, it is important to have accurate epidemiological data. Thus, we set out to obtain the prevalence and incidence rates of ON in Barcelona (Spain) from 2008 to 2012, by a retrospective evaluation of electronic hospital records at the Hospital Clinic of Barcelona (population of 300,000 in the catchment area) matching the following ICD-9-CM codes as search terms: 377.3-optic neuritis; 377.30-optic neuritis, unspecific; 377.31-optic papillitis; 377.32-retrobulbar neuritis, acute; 377.39-other optic neuritis and "optic neuropathy". Demographic and clinical data were collected from records with a confirmed diagnosis of ON, including cases of idiopathic ON, multiple sclerosis, neuromyelitis optica and CRION. The prevalence of acute ON on 31 December 2012 was 2.75 cases per 100,000 people. The mean annual prevalence of acute ON during the 2008-2012 period was 7.87 cases per 100,000 person-year and the mean annual incidence rate was 5.36 cases per 100,000 person-years. The incidence of ON in Barcelona during 2008-2012 was higher than previously reported. This increase may reflect the evolution of diagnostic criteria, the use of a referral-center approach instead of a population-based approach, increased awareness of demyelinating diseases, latitude-related factors and possibly a true increase in its incidence.