I am suffering with the same thing. I was diagnosed with and mangionoma on my left side years ago however I constantly feel pressure behind my right eye with terrible headaches always usually on the right side causes my right eye to droop.
I have had some optical nerve damage due to a couple small Strokes that I suffered for other reasons that we do not know the answer to yet. However after several MRIs and CTS there is no explanation as to why I feel a constant pressure behind my right eye with headaches. It's an ongoing battle and I feel your pain it is so frustrating not having any answers. And it seems like one test for one issue leads to another issue you have to deal with so I understand and I feel your pain I wanted you to know that someone is with you and thinking of you.