THanks for the question. If the blurring is only in one eye then it could be a primary eye problem. The fact that the imagining and VEP are normal is good. Patients that develop optic neuritis as a cause of visual blurring usually have a problem in just one eye and it can be detected on physical exam. The sudden onset is interesting but nothing sounds progressive.
Some patients develop something called pseudotumor cerebri or elevated intracranial pressure.
The elevated spinal pressure cause headaches and can cause some visual blurring. A spinal tap can measure the pressure to make sure it is okay. The eye doctor can usually see the swelling, however, on the optic nerve. Certain medications like tetracyclin can also be linked. You should talk to your doctor about a spinal tap.