Azeem Siddique, Hannah Taylor

Salford Royal Hospital, Salford, United Kingdom

Introduction

The optic nerve carries information from the retina to the visual pathways in the brain. Optic neuritis is inflammation of the optic nerve, which can be associated with various aetiologies including demyelinating lesions, autoimmune conditions, infections and other inflammatory processes. This article discusses the clinical presentation of optic neuritis as well as pathogenesis, investigation and management.

Epidemiology

Studies have estimated the incidence of optic neuritis to be around 5-6 in 100,000 (1,2). Risk factors for optic neuritis include age between 20 and 40 years, female sex (3:1) and Caucasian race (1).

Pathogenesis

Optic neuritis has been suggested to be a T-cell mediated inflammatory process (3). It can be idiopathic or secondary to an underlying pathology. Most commonly, optic neuritis is associated with demyelination of the optic nerve and can be the initial presentation of multiple sclerosis (MS). Patients with optic neuritis have around a 30% chance of developing MS within 5 years (1). Neuromyelitis optica (NMO) is another demyelinating condition that presents as recurrent, severe optic neuritis alongside transverse myelitis. Differentiating between MS and NMO is important for prognostics and management. Less common causes include infections such as herpes zoster, syphilis, and lyme disease as well as autoimmune conditions such as sarcoidosis and systemic lupus erythematosus (4).

Clinical Presentation

Optic neuritis most commonly presents with acute, unilateral loss of vision, usually progressing over the course of hours before improving to complete resolution over weeks to months (5). The nature of visual loss can vary from complete loss of vision in the affected eye to partial loss or blurred vision. Optic neuritis is typically painful, especially with eye movement, however pain can vary in severity (5). Patients with optic neuritis may notice impaired colour vision with colours appearing washed out in the affected eye. In particular, the colour red can be affected, known as red desaturation (5). As with other demyelinating diseases, Uhthoff’s phenomenon may also be noted in optic neuritis: the worsening of vision with increased body temperature such as with a hot bath or physical activity (6).

Ophthalmological examination can provide objective evidence of optic neuritis through the swinging light test. In this test a source of light is swung back and forth between each eye and the direct and consensual pupillary light reflexes are observed. In unilateral optic neuritis, the relative afferent pupillary defect (RAPD) may be observed whereby the pupillary reflexes when shining the light into the affected eye are weaker than the unaffected eye. This can be observed as the pupil dilating when moving the light source from the unaffected eye to the affected eye. In most cases, fundoscopy reveals a normal appearance of the optic disc however a mild papilloedema may be seen in around 33% of patients (5).

A detailed history and full neurological and ophthalmic examinations are vital when suspecting optic neuritis. These can help to identify any underlying cause and can guide targeted investigation and management.

Investigation

Optic neuritis is largely a clinical diagnosis based on the patient’s presentation however the underlying aetiology can be determined through further investigation. Magnetic resonance imaging (MRI) with contrast of the optic nerve can confirm the presence of inflammation. MRI of the central nervous system can provide evidence of multiple sclerosis through detection of inflammatory white matter lesions.

Lumbar puncture can be used to give further information about the risk of developing multiple sclerosis with the measurement of oligoclonal bands in the cerebrospinal fluid (CSF). CSF testing can also be important if other infective or inflammatory causes of optic neuritis are being considered (4).

Testing for specific antibodies is also useful in cases of optic neuritis that may be due to autoimmune disease. In NMO, the serum levels of anti-aquaporin-4 antibodies may be raised. It is important to consider NMO in cases of recurrent or bilateral optic neuritis, or in an absence of white matter lesions on MRI of the brain (6).

Management

Management of optic neuritis aims to speed up recovery and restoration of vision. The optic neuritis treatment trial (ONTT) showed that intravenous methylprednisolone followed by oral prednisolone hastened recovery of visual loss, however the outcome in visual function was the same at 6 months in both placebo and intervention groups (7,8). The 15-year follow-up study of this trial showed that visual outcome was favourable in most optic neuritis patients despite treatment group (9). The ONTT found short term glucocorticoid therapy to be relatively safe despite minor side effects such as sleep disturbance, gastrointestinal disturbance, mood change and weight gain (10). Whether to treat patients with high dose corticosteroids should be considered on an individual basis and guided by neuro-ophthalmology specialists. In cases of atypical optic neuritis secondary to NMO, plasma exchange and immunotherapy may be required (11).

Conclusion

Optic neuritis is an inflammatory optic neuropathy that can be idiopathic or secondary to underlying disease. It usually presents with acute visual loss and ocular pain. Diagnosis is based on clinical assessment however targeted investigations can provide indication to the underlying pathology and help to guide management.

References

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2. Rodriguez M, Siva A, Cross SA, O’Brien PC, Kurland LT. Optic neuritis: a population-based study in Olmsted County, Minnesota. Neurology. 1995 Feb;45(2):244-50. doi: 10.1212/wnl.45.2.244. PMID: 7854520. 

3. Söderström M, Link H, Sun JB, Fredrikson S, Wang ZY, Huang WX. Autoimmune T cell repertoire in optic neuritis and multiple sclerosis: T cells recognising multiple myelin proteins are accumulated in cerebrospinal fluid. J Neurol Neurosurg Psychiatry. 1994 May;57(5):544-51. doi: 10.1136/jnnp.57.5.544. PMID: 7515411; PMCID: PMC1072912. 

4. Hoorbakht, H., & Bagherkashi, F. (2012). Optic neuritis, its differential diagnosis and management. The open ophthalmology journal, 6, 65–72. https://doi.org/10.2174/1874364101206010065 

5. E.J. Atkins, Optic Neuritis, Editor(s): Michael J. Aminoff, Robert B. Daroff, Encyclopedia of the Neurological Sciences (Second Edition), Academic Press, 2014, Pages 681-686, ISBN 9780123851581, https://doi.org/10.1016/B978-0-12-385157-4.00170-6. 

6. Wilhelm, H., & Schabet, M. (2015). The Diagnosis and Treatment of Optic Neuritis. Deutsches Arzteblatt international, 112(37), 616–626. https://doi.org/10.3238/arztebl.2015.0616 

7. Beck RW, Cleary PA, Anderson MM Jr, Keltner JL, Shults WT, Kaufman DI, Buckley EG, Corbett JJ, Kupersmith MJ, Miller NR, et al. A randomized, controlled trial of corticosteroids in the treatment of acute optic neuritis. The Optic Neuritis Study Group. N Engl J Med. 1992 Feb 27;326(9):581-8. doi: 10.1056/NEJM199202273260901. PMID: 1734247. 

8. Beck RW, Cleary PA, Backlund JC. The course of visual recovery after optic neuritis. Experience of the Optic Neuritis Treatment Trial. Ophthalmology. 1994 Nov;101(11):1771-8. doi: 10.1016/s0161-6420(94)31103-1. PMID: 7800355. 

9. Optic Neuritis Study Group. Visual function 15 years after optic neuritis: a final follow-up report from the Optic Neuritis Treatment Trial. Ophthalmology. 2008 Jun;115(6):1079-1082.e5. doi: 10.1016/j.ophtha.2007.08.004. Epub 2007 Nov 5. PMID: 17976727. 

10. Chrousos GA, Kattah JC, Beck RW, Cleary PA. Side effects of glucocorticoid treatment. Experience of the Optic Neuritis Treatment Trial. JAMA. 1993 Apr 28;269(16):2110-2. PMID: 8468765. 

11. SJ Hickman, CM Dalton, DH Miller, GT Plant,, Management of acute optic neuritis, The Lancet, Volume 360, Issue 9349, 2002, Pages 1953-1962, ISSN 0140-6736, https://doi.org/10.1016/S0140-6736(02)11919-2.