Optic neuritis may be asymptomatic or may present with the following symptoms [6]:

• Visual loss. Sudden, progressive and profound visual loss. 
• Pain above or behind the eye that increases on ocular movements, especially when looking up and down. The pain may last for several weeks.
• Visual difficulty is exacerbated in bright light.
• Impairment of color vision leading to patients complain of reduced vividness of colors or things looking “washed out”.
• Movement phosphenes and sound induced phosphenes. Patient complains of flashes or flickering of light.
• Uhthoff’s phenomenon: Episodic transient aggravation of visual loss on exertion and on exposure to heat, which recovers on resting or moving away from the heat. 
• Pulfrich’s phenomenon: Depth perception may be impaired, especially for moving objects.
• Difficulty in vison in low light conditions.
• Some patients may have normal central vision with complaints of loss of peripheral vision to one side in the superior or inferior fields.

The diagnosis of acute demyelinating optic neuritis is based on the history, symptoms and clinical signs from the following eye tests:

• Visual acuity: Visual acuity worsens over several hours,days or even minutes and may range from 20/20 to no light perception on examination. 
• Visual fields: A central scotoma is common. Less frequently, an arcuate scotoma, a superior or inferior altitudinal scotoma, peripheral constriction, a cecocentral scotoma, and bitemporal or a left or right hemianopic defect may be seen. 
• Contrast sensitivity and color vision: Both reduced, sometimes more severely than the loss of visual acuity. Color vision testing is preferably done with the Farnsworth–Munsell 100-hue test. 
• Pupillary examination: The relative afferent pupillary defect is almost always present in anterior (swollen disc) or retrobulbar neuritis, unless there is a coexisting optic neuropathy in the fellow eye or other causes of visual loss unrelated to an optic neuropathy. 
• Fundus examination: Lesions that are adjacent to the optic nerve head cause papillitis (anterior optic neuritis) with minimal blood vessel enlargement and rarely peripapillary hemorrhages. Vitritis is present in anterior optic neuritis caused by infections or inflammations and intermediate uveitis with multiple sclerosis. Retrobulbar neuritis does not produce papillitis. The presence of peripheral retinal venous sheathing has been shown to be correlated with the development of multiple sclerosis [7]. 
• Other diagnostic tests are magnetic resonance imaging (MRI), cerebrospinal fluid analysis, and serological studies, done in order to determine the cause in atypical cases and the prognosis or risk for subsequent development of multiple sclerosis in cases presenting with only optic neuritis. Contrast MRI of the brain is done to detect lesions in the white matter [8] [9]. 

In a patient having the first attack of acute demyelinating optic neuritis, in the presence of two or more white matter lesions on MRI (3mm diameter or larger, at least one lesion periventricular or ovoid), the recommended treatments is one of these [10]:

• Intravenous methylprednisolone (1g per day, single or divided doses, for 3 days) followed by oral prednisone (1mg/kg per day for 11 days, then 4-day taper).
• Interferonβ-1a (Avonex 30μg intramuscularly once a week). 
• Interferonβ-1a (Rebif 22μg subcutaneously once a week). 
• Betaseron (250μg subcutaneously every other day). 

In a patient with optic neuritis having fewer than two MRI white matter lesions, and in patients with established diagnosis of multiple sclerosis, and in patients with unilateral and severe visual loss or bilateral visual loss, treatment is intravenous methylprednisolone treatment followed by oral prednisone (as described above). This will hasten visual recovery but not influence the final visual outcome.

Intravenous methylprednisolone 1000 mg/day for 5 consecutive days followed by oral prednisone taper for optic neuritis with neuromyelitis optica.
Based on findings from the Optic Neuritis Treatment Trial, oral prednisone alone (without prior treatment with intravenous methylprednisolone) may increase the risk of recurrent optic neuritis and should be avoided.

Nonsteroidal anti-inflammatory agents may be prescribed for disabling ocular pain.
Treatment of the specific cancer in paraneoplastic optic neuropathy patients with chemotherapy and/or radiation therapy.

Even with no treatment, most patients of optic neuritis start to recover their lost vision within 2-3 weeks of the onset of symptoms, achieving the maximal improvement within 1-2 months or at the most within a year. Final visual outcome has been correlated with the initial severity of visual loss. In spite of visual recovery, patients continue to experience subtle visual problems which can be objectively documented as persistent defects in visual acuity, contrast sensitivity, color vision, visual field, visual-evoked potential and stereopsis.

In about 20% of patients, multiple sclerosis is associated with optic neruritis at the onset itself. Around 40% of affected individuals will develop multiple sclerosis at later stages. Recurrent episodes of optic neuritis in the initially affected or fellow eye may occur and the risk of recurrence is twofold greater in patients who are diagnosed with multiple sclerosis in the next ten years than in patients who do not develop multiple sclerosis [5].

These are the etiological factors associated with optic neuritis.

• Acute demyelinating disorders: The most common form of optic neuritis is acute demyelinating optic neuritis, which is often associated with multiple sclerosis. Other demyelinating conditions include neuromyelitis optica and diffuse periaxial encephalitis of Schilder. 
• Leber’s hereditary optic neuropathy
• Parainfectious: It can occasionally result from a local infectious process involving the orbits or paranasal sinuses. It may occur in association with systemic infections like measles, Epstein–Barr virus (EBV), herpes zoster, cat scratch fever, primary or secondary syphilis, Lyme disease, tuberculosis, HIV and cryptococcal meningitis in patients with AIDS [2]. 
• Autoimmune disorders: Behcet’s disease and systemic lupus erythematosus. 
• Malignancies: Leukemia, intraocular lymphoma, malignant melanoma and metastatic lesions spreading to the optic nerve.
• Inflammatory disorders: Sarcoidosis.
• Post vaccination: It may also occur following immunization with rabies vaccine, Bacillus Calmette–Guerin (BCG) and tetanus toxoid. 
• Idiopathic 
• Paraneoplastic syndrome: Acute demyelinating optic neuritis, without malignant invasion of the nerve itself, has been seen in bronchial carcinoma, oat cell carcinoma and lymphomas [3].

The annual incidence of optic neuritis is approximately 3–5 per 100,000 per year, while the prevalence is 115 per 100,000. The majority of patients who develop optic neuritis are between the ages of 20 and 50 years. Women are affected more commonly than men (2:1). In most cases, the pathogenesis of optic neuritis is inflammatory demyelination, whether or not multiple sclerosis is diagnosed clinically. Many cases where optic neuritis is the only presenting feature later are diagnosed with multiple sclerosis [4].

Although the exact underlying cause is unknown, the pathophysiology of acute optic neuritis and multiple sclerosis is that of primary inflammatory demyelination, substantiated by presence of abnormal intrathecal immunoglobulin G (IgG) synthesis in 60-70% of patients with isolated optic neuritis.

Regular follow up for future recurrences of optic neuritis as well as for future development of multiple sclerosis is important for timely management. A combination of azathioprine and prednisone has been used for the prevention of relapses in neuromyelitis optica.

Optic neuritis is an inflammation of one or both optic nerves, often associated with multiple sclerosis and demyelinating diseases. Adults and women are more affected. It clinically presents with the triad of reduced vision, ocular or orbital pain and impaired colour vision. Nearly full visual recovery over time is common but residual visual defects may persist. Intravenous steroids are given in severe or bilateral cases to speed up recovery. Patients with an isolated incident of optic neuritis have better final visual outcome, whereas the prognosis is worse for patients with recurrent attacks or multiple sclerosis [1].

Definition: Optic neuritis is an inflammation of the optic nerve, which is the nerve responsible for transmitting visual information from the eye to the brain. 

Cause: Optic neuritis is often associated with multiple sclerosis. It is believed that optic neuritis may have an autoimmune cause, where the body mistakenly destroys the nerve sheath (known as myelin) leading to nerve damage. Optic neuritis can also be associated with infections, neuromyelitis optica and autoimmune diseases. 

Symptoms:

• Pain above or behind the eyes, it may increase on looking up or down. 
• Sudden decrease in vision that rapidly increases over hours or days. You may notice a loss of vividness of colors. 
• Sensation of flashes or flickering lights. 
• The vision loss may be aggravated when you are very tired or when you take a hot shower or in presence of very bright light. 

Diagnosis: The eye doctor will take a detailed history of your symptoms and medical conditions that you and your close relatives have. A detailed examination of your eyes will be done, including an examination of the inside and back of the eyes with an instrument called ophthalmoscope. Magnetic resonance scans of the brain and eyes are often required. Blood tests may be required to rule out other diseases and infections. 

Treatment and follow-up: Optic neuritis often improves spontaneously and a large number of people regain their vision almost completely in a year. The doctor may give you steroid medication through veins. Steroids reduce the inflammation in the optic nerve and speed up the visual recovery, but do not improve the extent of lost vision that you will recover. Steroids will also be given if multiple sclerosis is suspected. You may have repeat attacks of optic neuritis in future. Presence of multiple sclerosis or neuromyelitis optica leads to poor prognosis for long term visual recovery and preservation.

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10. The clinical profile of optic neuritis. Experience of the Optic Neuritis Treatment Trial. Optic Neuritis Study Group. Arch Ophthalmol 1991; 109:1673.