Multiple Sclerosis (MS): This is the most common cause of optic neuritis, especially in young adults. MS is an autoimmune disease that affects the central nervous system, and optic neuritis is often one of its initial presentations.

Idiopathic Optic Neuritis: This refers to optic neuritis without a identifiable cause, which can occur in isolation or as part of a broader syndrome.
Neuromyelitis Optica (NMO): Also known as Devic's disease, NMO is an autoimmune inflammatory condition that predominantly affects the optic nerves and spinal cord.
Systemic Lupus Erythematosus (SLE): SLE is an autoimmune disease that can affect multiple systems, including the nervous system, and optic neuritis can be one of its manifestations.

Giant Cell Arteritis: Although less common, giant cell arteritis is a critical diagnosis to consider because it can lead to irreversible vision loss if not promptly treated. It typically affects older adults.
Sarcoidosis: This is an inflammatory disease that can affect multiple parts of the body, including the eyes. Optic neuritis can be a manifestation of sarcoidosis, and missing this diagnosis could lead to significant morbidity.
Infections (e.g., Syphilis, Lyme Disease): Certain infections can cause optic neuritis, and failing to diagnose them could result in severe consequences, including blindness and neurological damage.

Leber's Hereditary Optic Neuropathy (LHON): A rare inherited form of optic neuritis that primarily affects young adult males, leading to severe vision loss.
Toxic or Nutritional Optic Neuropathy: Caused by exposure to certain toxins (e.g., methanol, ethambutol) or nutritional deficiencies (e.g., vitamin B12 deficiency), these conditions can mimic optic neuritis.
Optic Neuritis due to Malignancy: Rarely, optic neuritis can be associated with cancer, either directly (e.g., optic nerve glioma) or indirectly (e.g., paraneoplastic syndromes).