Neuromyelitis optical spectrum disorders (NMOSD) are rare autoimmune neuroinflammatory diseases spanning a broad age range. They are clinically characterised by recurrent attacks of optic neuritis (ON), myelitis and less frequently by the brainstem and cerebral attacks, and profoundly impact patients’ quality of life. 1–4 The current concepts of NMOSD are rapidly changing. An international panel of experts published the latest NMOSD diagnostic criteria in 2015. 5 Pathogenic serum autoantibodies against aquaporin-4 (AQP4-IgG), an astrocytic water channel protein, can be detected in 60%–80% of patients with NMOSD. 6 7 The diagnostic criteria differentiate patients with positive or negative/unknown AQP4-IgG status. In the latter case, strict rules apply to the clinical presentation and paraclinical findings, in particular those from MRI for diagnosing NMOSD. 5 8 In some AQP4-IgG seronegative patients within the NMO disease spectrum, for example with isolated recurrent ON or myelitis, serum antibodies against myelin oligodendrocyte glycoprotein (MOG) can be detected. 9–12 As a different cellular target is involved, most experts consider MOG-IgG autoimmunity, or MOG-IgG-associated encephalomyelitis, as a separate disease entity, pathogenetically distinct from classic AQP4-IgG-associated NMOSD. 13–15 The term myelin oligodendrocyte glycoprotein antibody disease has recently been proposed for this disorder. ON is one of the most common clinical manifestation of NMOSD. ![]() It frequently results in severe structural optic nerve damage and visual impairment, often occurs bilaterally, with common relapses. 3 17 18 Patients often develop a visual disability as a result of decreased high-contrast visual acuity (HCVA) and low-contrast visual acuity, as well as colour and visual field defects. These functional limitations result in impaired vision-related quality of life and a high incidence of legal blindness. Optical coherence tomography (OCT) acquires high-resolution retinal images and plays an important role in assessing ON-associated damage in NMOSD 22 and other neuroinflammatory disorders associated with ON. ![]() 23 24 After transection of optic nerve axons following acute ON, retrograde neurodegeneration leads to neuroaxonal damage in the retina. ![]() Retinal post-inflammatory neuroaxonal degeneration typically progresses for about 6 months after the onset of acute idiopathic ON. It can be assessed by OCT as peripapillary retinal nerve fibre layer thickness (pRNFL) or ganglion and inner plexiform layer thickness (GCIP). 26 Due to the rarity of NMOSD, adequate disease-specific studies on temporal ON dynamics are scant.
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