Acute optic neuritis (Retrobulbar neuritis): Visual loss associated usually with a central scotoma and recovery over some weeks. This disorder commonly occurs in young adults. The visual loss develops over several days and is often associated with pain on ocular movement (irritation of the dural membrane around the optic nerve). In milder forms, only colour vision is affected. Typically only one eye is affected, although occasionally v both eyes simultaneously -VT>; Macular area or consecutively are involved. Macular
Acuity is usually fibres more than 6/24.
On examination: Disturbance of visual function ranges from a small central scotoma to complete loss. Fundal examination reveals swelling - papillitis - in up to 50% of patients, depending upon the proximity of the plaque to the optic nerve head.
'Sheathing' from an inflammatory exudate around peripheral retinal venules is common. Reduced visual acuity distinguishes papillitis from papilledema. Investigation-. Visual evoked responses (VERs) show delay. High resolution CT or MRI of the optic nerve excludes tumour. MR confirms the presence of plaque.
Treatment: Steroids shorten the duration of visual loss and ease pain when present. I.v. methylprednisilone not only speeds recovery but may delay the development of MS.
Outcome: 90% of patients recover most vision, although symptoms may transiently return following a hot bath or physical exercise - Uhthoff s phenomenon. Following recovery the optic disc develops an atrophic appearance with a pale 'punched out' temporal margin.
- No evidence of multiple sclerosis occurs in patient's lifetime.
- Symptoms and signs of demyelination elsewhere in the nervous system follow - multiple sclerosis.
Over a 5-year period from presentation, 75% of patients fall into the last group. Onset in winter, the presence of 'silent' cerebral lesions on cranial MRI and the presence of certain histocompatibility antigens, e.g. HLA DR2, increase the risk of subsequent MS.
Acute bilateral optic neuritis: less common than unilateral disease and progression to MS not as likely. Occasionally followed by a transverse myelitis (Neuromyelitis optica, page 509). Examination of mitochondrial DNA distinguishes from Leber's hereditary optic neuropathy (page 531).
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