Patch of vision in left eye kept disappearing, more if i bent over or beared down. opthamologist said back of eye looked normal, might be vascular but wasn't concerned. worried could be aneurysm?

Get a second opinion: This is not to be ignored. See another ophthalmologist and soon.

Valsalva?: You may be experiencing a valsalva reaction as you bear down and strain. This may affect blood pressure to your brain which may make you feel dim in vision, dizzy, or a faint feeling. It looks like your md is evaluating your heart ; bp, ; eyes ok. Maybe a neurologist could help to rule-out a structural problem, particularly if this is frequently occurring.