Many people with double vision, or diplopia, want a CT scan or MRI to see if it is caused by a brain tumor or other serious problem. Much of the time, following a comprehensive eye evaluation, neither test is necessary. The most common causes of double vision are refractive error, dry eyes, cataract and non-neurologic eye misalignment; all readily diagnosed by a complete exam. Only a minority of cases of diplopia result from problems within the brain.