This study evaluates the length of optic nerve lesion on 3D-DIR sequence as an imaging biomarker predictive of retinal axonal loss and visual disability, 12 months after the occurence of a first clinical episode of optic neuritis.

Neurologists and Neuro-Ophthalmologists are in need for reliable and robust imaging biomarkers enabling to predict retinal axonal loss and visual disability after clinical episode of optic neuritis (ON). Length of optic nerve lesion measured on MRI may be one of them.

The aim of our study is to measure the association between the extent of inflammatory demyelinating process on optic nerve at the acute of ON and the retinal degenerative process following optic nerve injury.

The investigators planned to include 50 patients suffering from a recent clinical episode of ON.

Extent of demyelinating inflammatory process will be assessed by the length of optic nerve double inversion recovery (DIR) hypersignal at the acute phase of ON.

The axonal degenerative process following optic nerve demyelinating injury will be assessed by retinal atrophy measured on optical coherence tomography at 12 months after ON, by visual disability measured on low vision contrast acuity scale and by microstructural quality analysis of optic nerve measured on diffusion tensor imaging sequence of the optic nerve.

Inclusion Criteria:

• patient suffering from an acute clinical episode of optic neuritis (ON) confirmed by neurophthalmological examination
• < 2 months between start of acute episode of ON and inclusion

Exclusion Criteria:

• past history of homolateral episode of ON
• retinal diseases
• diabeta mellitus
• pregnancy

Patients suffering from a recent clinical episode of ON suggestive of demyelinating disease as clinically isolated syndrome, multiple sclerosis or neuromyelitis optica spectrum disorders.