Hello, I have gone through your query and understand your concern. Yes. As you suspected this may due to the Secondary metastasis in brain from some other primary tumor may cause double vision and Equilibrium imbalance. But it is essential to find the primary tumor by through physical examination and further investigations like Ultrasound abdomen, X-ray Chest. You must get full evaluation of ear and eye by various investigations to rule out any local disease which may affect the balance. This need through examination by Ophthalmologist and ENT Physician. If every this is normal pertaining to this system, You need the investigations which i mentioned above. Then based on the primary tumor or other cause, treatment varies. Hope this helps. Please write back for further queries. Wishing you good health.