My 68 yr old mother in law has sudden onset flashing, zig zagging lights in left eye. no prior history of migraine or stroke, no high bp or any other conditions, not on medication, no other symptoms. under a lot of stress. er or can it wait ?

Eye exam or ER: If a new vision symptom pops up, one should see her primary care doctor and/or an ophthalmologist (MD eye doctor). Vision is vitally important, so it is good to have a doctor get the whole story and examine the eyes. That said, sudden onset flashing and zigzag lights in an elderly person means an Ophthalmologist exam right away (may need to go through the ER) to make sure the retina is still ok.