In the review I read, 45% of cases were due to tumors, 15% due to elevated intracranial pressure but not a tumor, 12% due to trauma, 11% present from birth, 7% inflammatory, miscellaneous 5% and unknown cause 5%. In this case with a normal MRI, it is important to have a lumbar puncture to rule out increased intracranial pressure and to rule out inflammatory causes. Lots of blood test should help also to rule out inflammatory causes. I have also read cases with a viral cause. I'm sorry but I don't know the prognosis but my feeling is that the main thing to worry about here is a tumor and that has been ruled out. I have seen dozens and dozens of adults have complete improvement of a 6th nerve palsy after a few months (usually due to hypertension or diabetes or both) so I hope this case follows that pattern of improvement.
Thank you so much for your info. Today he has told me that there have been changes in his double vision. Where the double images used to be separated, they are now overlapping. Do you think that this may be an indication that the condition is beginning to improve? As an aside, both opthamologists and his pediatrician are in agreement that there is no evidence of increased intracranial pressure due to lack of other symptoms and they have decided not to order the lumbar puncture.