Hi.
Thanks for your query and an elucidate personal and family history.
You have been suffering from intermittent
double vision, do wear bifocals which do not last for long and have
tiredness too.
Your family history of mother died of medulla
blastoma, grandson is a recovering clear cell sarcoma and maternal grandmother died of carcinoma definitely is a strong family history of cancer.
Hence your case of double vision can be correlated with a chance of a tumor in the brain in mid-line or near the
Optic nerve or skull base causing problem with
cranial nerve affection causing your symptoms.
I would advise you the following:
Clinical evaluation and examination by an Ophthalmologist.
MRI of the brain and the base of skull, eyes and sinuses should give you the diagnosis as well as plan for treatment.