The clamp hurts, but it is bearable. You can see, but everything is quite blurry. The suction ring puts pressure on the eye and your vision goes black for a moment. During the actual laser ablation I saw dim flashes of deep violet.
They explain everything to you before hand as well.
My wife had laser surgery and her biggest complaint was the "sand in eye" feeling. She also had a very small amount of light sensitivity afterward. It only lasted for about a week and now her vision is just about perfect. She can see better then me now and I was told I have 20/20 vision at my last appointment. She would do it all again in a second and has no regrets. I don't think you will either.