From the Guidelines

Optic neuritis is often associated with multiple sclerosis, as it can be the initial manifestation of the condition.

Optic neuritis is defined as an acute inflammatory condition of the optic nerve, which can be unilateral or bilateral, and is often seen as the initial manifestation of multiple sclerosis 1.
The primary differential consideration for optic neuritis includes multiple sclerosis, neuromyelitis optica, neuromyelitis optica spectrum, or other infectious or granulomatous conditions 1.
Optic nerve imaging can be helpful in confirming optic nerve involvement in multiple sclerosis and can exclude alternative diagnoses for atypical optic neuropathies 1.
Typical acute optic nerve lesions are characterized by T2 hyperintensity, associated optic nerve swelling, and contrast-enhancement, but these findings are not multiple sclerosis-specific 1.
Red flags for the optic nerve include posterior optic nerve involvement, simultaneous bilateral optic nerve involvement, and a long optic nerve lesion, which can be suggestive of neuromyelitis optica spectrum disorders or anti-MOG-IgG disease 1.
A T2-hyperintense lesion in the nerve can differentiate multiple sclerosis from ischemic and toxic optic neuropathies or Leber’s hereditary optic neuropathy 1.
Optic neuritis can also be secondary to demyelinating disorders, other inflammatory, infectious, or granulomatous disorders, or unknown underlying cause (idiopathic) in children 1.

From the Research

Optic neuritis may occur during the course of several neurologic and systemic disorders, including multiple sclerosis 2
In many patients, signs and symptoms of multiple sclerosis occur after an episode of optic neuritis 2
Optic neuritis is an inflammatory optic neuropathy that is commonly indicative of autoimmune neurological disorders, including multiple sclerosis 3
The relationship between optic neuritis and multiple sclerosis is still controversial, with several risk factors for development of multiple sclerosis identified, but the exact relationship remains unclear 2

Optic neuritis is characterized by reversible central visual loss, and may be accompanied by pain with eye movements, dyschromatopsia, and a relative afferent pupillary defect 4
Magnetic resonance imaging (MRI) is an important investigation for assessing an associated risk of multiple sclerosis 4, 5
Optical coherence tomography (OCT) can provide additional details on the course and functional outcome of optic neuritis, and may contribute to the relationship between optic neuritis and possible associated multiple sclerosis 4, 5

Regaining high-contrast visual acuity is common in people with idiopathic optic neuritis and multiple sclerosis-associated optic neuritis, but residual deficits in contrast sensitivity, binocular vision, and motion perception may impair vision-specific quality-of-life metrics 3
Early clinical recognition of optic neuritis is important in determining the potential aetiology, which has bearing on prognosis and treatment 3
Guided by early and accurate diagnosis of optic neuritis subtypes, the timely use of high-dose corticosteroids and, in some instances, plasmapheresis could prevent loss of high-contrast vision, improve contrast sensitivity, and preserve colour vision and visual fields 3