I'm not really sure, but anything that you have digged yourself a hole into (including blindness, holes in the heart, etc) am sure can be healed. We just don't have the information.
What I do know is the skin is an organ that offers protection, sweat glands, hair follicles, etc. I've read some people getting rid of stretch marks and scars (even keloids!). This is what I've read from Fonty for one who had his stretch marks and scars fade. But there are other people with the same experience, not just Fonty.