Hello and thanks for your question.
I'm assuming that there wasn't any specific nerve damage that the double vision was attributed to (at least that you were told about) because the double vision resolved after just a few days.
Many people have a predisposition to not keeping their eyes straight together all of the time; this predisposition tends to happen since birth and usually manifests at times when the brain is busy doing something else (such as when you're sick, very fatigued, inattentive, or inebriated). People with this predisposition have varying degrees of this and for some it is worse than others. I suspect that (again, outside of any specific nerve damage) you are one of these people and that the brain was certainly "busy" healing from brain surgery, which was why you saw double during that post-operative recovery time and why it went back to normal after you were finished healing.
It may be that your ability to keep the eyes straight together is lessening and therefore your eyes are starting to cross. If you are farsighted or do not have significant near-sightedness, then you are probably needing some sort of reading glasses by now. If not, this may be another impetus for the eyes to cross in; that is, if you're reading without reading glasses and you're not nearsighted.
Of course, without being able to give you a complete exam I unable to say with any degree of certainty that there is not some other pathology going on, but this is one of the most likely scenarios that his happening. If your eye specialist has given you a complete exam with respect to this double vision and didn't find anything wrong, then this may very well be the reason why.
As far as the white on the optic nerve, this is very often due to what is called myelinated nerve fibers on the optic nerve, which is a normal variant, does not cause vision problems, and does not require any treatment or monitoring; it is just a different way for the optic nerve to appear.
Does this help address your concerns?
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My opinion is solely informative and does not constitute a formal medical opinion or recommendation. For a formal medical opinion and/or recommendation you must see an eye doctor.