Hi. I'm online and happy to answer your question today.
It is difficult to know if the advice/diagnosis of optic neuritis is correct without actually having a look at you, but that is consistent with what you are saying.
I believe that the apparition you are seeing is from what is called an entoptic phenomenon. This happens normally in certain circumstances and can also occur with damage to the visual system. It is caused by your brain trying to "make sense out of" the abnormal signals that it is receiving from the damaged tissue, in this case, your optic nerve.
I do not see the need for a second opinion at this time as you have already got an opinion from a doctor best trained to diagnose and treat this condition.
Does this make sense to you?
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Do you agree with this diagnosis and prognosis from this doctor, or in your professional opinion, is there something you'd like to add in the form of advice?