Hi and welcome
I would strongly suggest you get a sec0nd opinion with a neurologist who specialises in MS, if only for your own peace of mind if you are having doubts. A second opinion would likely provide you with a more definitive answer in regards to where you are in regards to already having MS or not....
Optic neuritis is one of the most common presenting clinical signs of MS, and whilst the odds of developing MS over the preceding 5 to 10 years increase, it can definitely be a stand alone dx too.....its pretty standard to need 6mthly/12mthly/24mthly brain and spinal cord MRI's and even visual nerve conductor tests to track of any newly developing MS related diagnostics.
Over the years the MS diagnostic criteria has been tweaked multiple times to make MS easier to dx much earlier but neurologist MS experience can still impact the outcome.
"“Evidence of damage “disseminated in space,” or found on two or more parts of the CNS” – and so far I only had the optic neuritis as a symptom?"
Optic neuritis (ON) is an objective clinical sign and definitely hard diagnostic evidence but symptoms are generally not seen as 'clinical' signs of an attack which is what 'evidence of damage' etc means. Below is a link to the basic diagnostic criteria, and you'll see somethings in your brain MRI report that is the same or similar.....
Have you ever had a spinal MRI?
Hope that is of some help....JJ