Maybe you might want to try a few adjustments on your powerheads. (was going to say "play with your powerheads" but that sounds perverted
) By changing the amount of suface aggitation, you will change the shimmer effect, (slower/faster, smaller/bigger flash ect) I'd play with this. You may get a differant shimmer you can watch without a headache. Just beware, less surface aggitation means less gas exchange. Don't know, just an idea. But definately get a medical opinion on this. Hate to see you have an epilectic seisure or another condition you didn't know you had.