So far, I didn't see any resourcese about the damages to eyes from holographic sights. Holographic technology is still developing and improving. People are still studying on it, so there is no other information about damages from it. I think it should be ok. Projector is very bright. As long as you don't directly look at the projector, it is fine.
Yes, using too much holographic sights is bad to your eyes because your eyes vision will be shrinking to smaller ones and the affection of the coming images' process. In order to prevent it, you could see things far away before and after you use the holographic sights. You need to use the warm compress to make your eyes feel comfortable and become moisture.