Im looking for a book about parallel worlds

Question

So there is this book I read a while ago on Kindle unlimited and forgot about, and now cant find the name because KU doesn't store books that you have already read :(

It is about this guy who gets teleported to another world and loses an eye in the process, ends up in a prison in this other world, and this guy with an emerald for an eye uses some healing power to heal the dudes eye but turns it into a diamond/crystal? they escape the prison and join up with a resistance or something. Basically certain people have gemstones for eyes that relate to specific powers, like healing is emerald, violet is emotion, idk.

Answer 1

I think that's Gemworld.

I remember it matching all the plot points you call out (transported to alternate world, prison, escape, join the resistance, gemstone eyes). I also seem to recall it had strong Christian Fantasy leanings.

Also, check this out for KU history.