Wiktionary
optic neuritis
n. The inflammation of the optic nerve that may cause a complete or partial loss of vision.
Wikipedia
Optic neuritis
Optic neuritis is a demyelinating inflammation of the optic nerve. It is also known as optic papillitis (when the head of the optic nerve is involved) and retrobulbar neuritis (when the posterior of the nerve is involved). It is most often caused by multiple sclerosis, and it may lead to complete or partial loss of vision in one or both eyes.
Partial, transient vision loss (lasting less than one hour) can be an indication of early onset multiple sclerosis. Other possible diagnoses include: diabetes mellitus, low phosphorus levels, or hyperkalaemia.