Hi. I'm online and happy to answer your question today.
I would not expect a problem that is limited to your eyes to cause issues with mental clarity....that really sounds like a central nervous system issue.
That also goes for the problems you are having with your neck....
should I see my GP in order to get mri scan?
Now, as far as the issues with blurry vision, especially with things on a white background that can be caused by a number of anterior segment issues, such as dry eyes (which you are already somewhat addressing), allergies and blepharitis.
I wouldn't jump to an MRI until there is a specific issue that needs looking at. Just getting a random MRI without knowing what you are looking for is usually non-productive.
what should I do see GP or
That being said, a visit to your GP to workup your symptoms sounds like a good idea. While you wait I would try some home remedies for the possible anterior segment issues.
I'd see your GP first.