Thank you for providing additional information.
There are many things that may have caused this optic nerve swelling. Optic neuritis and papilledema are the most common, but other things can cause this as well. A viral optic neuropathy is consistent with all of the negative tests you have found.
Given the lack of positive test findings for this problem, I think it would be prudent for you to seek a second and maybe even a third opinion. I would start with a neuro-ophthalmologist. Usually you have to go to a major medical center to find one, but that is your best bet. At the very least, however, I would recommend seeing a different ophthalmologist for a second opinion, one who will do their own workup and not rely on that which has been done previously.
The examination is such a crucial part of this problem so for me to list the dozen or so things that can cause this would do you no good. Your anxiety is justified and I think the second opinion is the most appropriate course of action right now.
As far as the brain finding new pathways: the brain is unlikely to form significant new pathways that will lead to near-normal vision again in that eye. I suspect the retinal specialist just meant that over time, the brain can learn how to use the vision that is left in that eye to the fullest.
Does this better address your concerns?
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Disclaimer: My opinion is solely informative and does not constitute an informed medical opinion or recommendation. For an informed medical opinion and/or recommendation you must see an eye doctor.