The advice I got from my first neuro was simple:
If it lasts for more than 24 hours, make a note.
If it lasts for more than a week - get on the phone right away
Now you are up against the old criteria - less than two years between relapses …
Compared to the new thinking - treat as soon as possible!
The bit of the optic nerve that cannot be seen is that outside of the eyeball.
What really tells one what is going on is the VEP Test (Visually Evoked Potentials). This measures any difference in transmission speed down the optic nerves for each eye.
If there is a difference, then it’s Optic Neuritis, or just plain old MS. In the US, the VEP test is now preferred to a LP as a diagnostic aid, in that it will pick up any differences a lot sooner - and you cannot influence the result at all.