I was diagnosed with optic neuritis about 2 years ago. I don't know if it came on suddenly, or I suddenly noticed it. Because I wear glasses, i'd just had the persistent feeling that my lenses were grubby -- until I realised it was my eye. It was as though I was looking through steam, plus my colour vision had gone. I understand now these are "classic" symptoms -- the doctor barely even had to look at me to make the diagnosis. But I did take a test, involving seeing dots of lights, to see how badly I was affected.
Apparently about 50% of cases are linked to ms, and the other 50% are unknown cause. I wonder if perhaps a lot of the cases that are not associated with ms just don't get registered, as people wait for it to go away and, with no other symptoms, don't bother seeing a doctor.
In any case, my risk factors were contradictory: I was over 40, so past the usual age of onset, but my father had ms, so I am at high risk. Having had no other symptoms, the doctor opted not to do any mris, etc.
It took a few months for my vision to go back to normal. The "steam" effect probably lasted about three weeks, gradually dissipating, but I didn't see red and yellow again for six months.
So far, no further episodes.
I would say also that, having had the scare, I have done a lot of research to see if I can avoid any other ms-related symptoms. First, the most important thing is to massively increase your vitamin d intake. That means getting out in the sun for at least half an hour a day, and take supplements. I take about 800 iu a day, roughly 4 times the minimum requirement. The reason for that is the clearest epidemiological link with ms is in latitude: people who live close to the equator are much less likely to get ms, and the further from the equator, the more likely you are to get it. Further, the main exception to this relationship is in areas where people eat a lot of oily fish, which is very high in vit. D. It is possible that people who are at risk for ms do not process vit. D properly, and so need to ingest more. Vitamin d regulates the immune system, so a lack of it may allow the immune system to go haywire.
I also am eating a lot of linseed (flaxseed), which is one of the best sources of essential fatty acids, and take lecithin supplements, which help with nerve health.