Hi. I'm online and happy to answer your question today.
Everyone thinks brain tumor first :) You, from what you have told me, don't have one.
The number one cause for your problem is physiologic anisocoria. Sure there are a lot of pathological things that can cause differences in pupil size but I feel very confident in saying that after two complete eye examinations by ophthalmologists, imaging of your nerves and an MRI you are just fine.
Do not worry. Ok? Ok. You are fine.
Does this make sense to you?
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I see that you are offline. We can use the Q&A system to 'text message' each other. An email will be sent to each of us every time something is posted to this thread.
I am worried about physiologic anisocoria. Should I get another MRI since my last one was about 10 months ago or should things stil be the same? Could something bad have developed in that amount of time? Why would this have started to happen all of a sudden out of nowhere? Does physiologic anisocoria just come on suddenly like that?