Why can optic neuritis be an early sign of multiple sclerosis?

Optic neuritis is frequently an early sign of multiple sclerosis (MS) because the optic nerve and retina are embryonically extensions of the brain, making the eye a common site for the disease to manifest.12

In multiple sclerosis, the sheaths of the nerves become altered, which interferes with the transmission of nervous impulses. Because the optic nerve is a frequent target for this process, sudden loss of central vision or eye pain often serves as the initial symptom noticed by the patient.21

This presentation is significant because MS is characterized by long periods of remission; other neurologic signs of the disease may not become apparent for years—sometimes a decade or more—after the initial episode of optic neuritis. Consequently, a detailed ophthalmic examination is essential when a patient is suspected of having a central nervous system disease, as visual defects can provide the earliest evidence of the underlying condition.321