I had a personal experience with this in my 20s. I was in a situation where I was working on a project that left me working long shifts in a dim area, and started having peripheral flashes of light. That's a sign of retina detachment, so I was rushed off to the ophthalmologist. They went through a bunch of stuff and it turned out I was ingesting extreme amounts of aspartame. (>12 cups of coffee and 8-10 Diet Cokes a day) From a medical POV, more than 4 cans of diet soda is considered "high" use. I stopped sweetening coffee and moved to seltzer the next day and the symptoms were gone in 48 hours.

Diet Soda is bad stuff for many reasons. You're better off with drinking sugared soda or beer.