Optic neuritis (ON) is inflammation of the optic nerve.Classically there is a triad of clinical features – reduced vision, eye pain and impaired colour vision.
Acute demyelinating optic neuritis is a common cause of optic neuritis in parts of the world where multiple sclerosis is common. However, there are many other possible causes which must not be overlooked, as they may require different and urgent management.
The term ‘optic neuritis’ means inflammatory optic neuropathy from any cause, but is sometimes used to refer to acute demyelinating optic neuritis.
- Posterior scleritis
- Big blind spot syndrome
Presentation, assessment and diagnosis
The usual presentation is a triad of:
- Visual impairment
- Eye pain
- Dyschromatopsia (impairment of colour vision)
Other symptoms present in acute demyelinating optic neuritis are:
- Light flashes (phosphenes or photopsias).
- Uhthoff’s phenomenon – increased symptoms with raised body temperature (hot environment or exercise).
- Pulfrich’s phenomenon – altered perception of the direction of movement, due to asymmetrical conduction in optic nerves.
- Fatigue – fading of vision.
- Full ophthalmological and neurological examination by one of our Neuro-ophthalmologists.
- In practice, it is important to assess whether the clinical picture is typical of ADON, or whether there are atypical features suggesting another cause.
The diagnosis of acute demyelinating optic neuritis (ADON) is a clinical one. If the clinical picture is typical for ADON, initial assessment involves:
- Full ophthalmological examination.
- Testing of visual acuity, contrast and colour vision, visual field testing.
- MRI of the brain may be used to give information about the likelihood of developing multiple sclerosis (MS) (see below).
- Some studies suggest that testing of contrast vision, using specific charts, may yield similar information to MRI in this scenario.
- If there are atypical features, investigations depend on the clinical picture, and may include:
- Blood tests – eg full blood count, erythrocyte sedimentation rate, autoantibodies and syphilis serology.
- Serological testing for neuromyelitis optica immunoglobulin G (NMO-IgG).
- Chest X-ray – for suspected sarcoidosis, tuberculosis or malignancy.
- CT or MRI of brain and orbits.
- Lumbar puncture – for suspected central nervous system infection or inflammatory optic neuritis (cerebrospinal fluid is examined for immunoglobulins, oligoclonal bands and infection).
Acute demyelinating optic neuritis in adults
- Acute demyelinating optic neuritis demographics closely follow those of multiple sclerosis (MS), which has a higher frequency in Caucasian populations and at higher latitudes. Children who migrate before puberty take on the MS incidence of the area to which they migrate.
- Annual incidence of acute demyelinating optic neuritis is approximately 5/100,000; prevalence is 115 per 100,000.
The pathology of acute demyelinating optic neuritis involves demyelination and axonal loss, probably due to an inflammatory process and a delayed hypersensitivity reaction. Recovery is due to remyelination and compensatory neuronal recruitment.
- You will require a referral to one of our Neuro-Ophthalmologists
- They will consider corticosteroids during the acute phase:
- Treatment with methylprednisolone speeds up visual recovery in the acute phase, but has no effect on final visual acuity. Side-effects of corticosteroids can be serious. Therefore, they are usually reserved for patients who need to hasten visual recovery, such as those with poor vision in the fellow eye or bilateral visual loss, or for occupational reasons.
- Recommended treatment is methylprednisolone 1 g daily for 3 days.
- Oral prednisolone is not recommended because of (uncertain) evidence that it may increase the recurrence rate.
- There is no treatment that can reverse poor visual outcome in the long-term.
- Information for patients is important (see prognosis section below).
- Consider brain MRI, to give information about the risk of developing MS.
- Consider referring to a neurologist for assessment of the patient’s risk of developing MS, and the value of disease-modifying drugs in this context (see ‘Role of disease modifying drugs’, below).
- For the Pulfrich phenomenon (disturbed perception of movement, above), symptoms may be helped by using spectacles with a tinted lens over the unaffected eye, to balance the delay in conduction from the other side.
- For Uhthoff’s phenomenon symptoms (worsening vision with raised body temperature), avoid hot environments and take cool drinks; reassure patients that this symptom is reversible and does not further damage vision.
- The prognosis for vision in acute demyelinating optic neuritis is usually good.
Risk of developing MS:
- acute demyelinating optic neuritis is associated with MS.
- In the Optic Neuritis Treatment Trial, for adults with a single episode of unilateral acute demyelinating optic neuritis, the risk of MS was 38% at 10 years after onset, and 50% at 15 years. Another study found the MS risk was 54% after 30 years. The risk of developing MS is lower for children and for men.
- MRI of the brain gives information about the risk of developing MS. The presence of white matter abnormalities increases the MS risk and their absence reduces it. In the Optic Neuritis Treatment Trial, the risk of developing MS at 15-year follow-up was 25% for patients with no lesions on MRI, and 75% for those with white matter lesion(s).
Role of disease-modifying drugs:
- Interferon beta increases the time interval to relapse in MS. Trials suggest that, in a scenario such as a patient with acute demyelinating optic neuritis and white matter lesions on brain MRI, where the risk of developing MS is relatively high, interferon beta may similarly delay the onset of MS symptoms.
- However, bear in mind that:
- Many patients with a first episode of acute demyelinating optic neuritis and an abnormal MRI scan will not develop MS.
- Treatment is only partly effective, eg 6 years of interferon beta treatment prevents one relapse.
- The visual prognosis is good even if MS develops.
Your doctor will be able to discuss diagnosis, treatment and prognosis in more detail. The information contained here is general only, and aspects of diagnosis and management will vary according to your particular circumstances.
(Text sourced from: http://www.patient.co.uk/doctor/acute-optic-neuritis.htm)