My uncle (65) she had a fall and hit his head 2 months ago. 2 ct scans came out fine. later that week he developed double vision, he went to the ophthalmologist and he said the problem is not in his eyes. ordered mri. what could it be causing this?

Probably a 4th cranial nerve palsy. The 4th cranial nerve is subject to injury from blunt head trauma, such a falling, whiplash injury, or just bumping your head on a cabinet. Usually the double vision is vertical and is worse when looking away from the affected eye. There might also be a tilted component. The nerve regrows spontaneously over a period of months. MRI rules out more serious causes.