What Causes Visual Disturbances Along With Migraine?

I am experiencing sudden onset visual disturbance, primarily in my left eye field of vision, like a wave, water, or a shimmering. I have been experiencing migraines over the last few months but none recently. I had CMP and TSH last week which were normal, and began an exercise program to lose weight. I have gained 20 pounds in the last 6 months which is unusual for me. The visual disturbances came while I was driving and were very disturbing. They persist and it has been approx. 30 minutes now, worse in bright light. {42 yr old female)