CRP and Leber hereditary optic neuropathy: LHON: Leber hereditary optic neuropathy; DOA: dominant optic atrophy; MS: multiple sclerosis; MRI: magnetic resonance imaging; NMOSD: neuromyelitis optica spectrum disorder; NAION: non-arteritic anterior ischaemic optic neuropathy; AAION: arteritic anterior ischaemic optic neuropathy; GCA: giant cell arteritis; ESR: erythrocyte sedimentation rate; CRP: C-reactive protein; TNON: toxic and nutritional optic neuropathy