Yes, I have them cover my eyes with a rag that I can't touch, of course, BEFORE I slide into the MRI machine. Then even if I open my eyes at all, I still can't see a thing. Works like a charm!
But no, don't feel bad. I backed out of a clinical trial, also, because I decided to try something else, and I felt bad at first, too. There will be other opportunities to help the "MS cause" presented to you in many ways.
The MS Walk and other charitable things are just one example.