If you see the eye caps in the sheds then they aren't being retained. It puzzle's me to hear you say that you are seeing them every shed but a vet is telling you that the snake is retaining them. Can you get a second opinion? P.S. A pic of this would help out tremendously. It's tough for us to help out when we can't see the problem that you are having. I understand that you say your camera stinks but some type of pic would be better than nothing. Until then I think we are just taking shots in the dark with the problem. If the snakes eyeball is dented in I would also have to say humidity. Any time I have had a snake retain an eye cap I can see it without having to get the light just right. But you are doing the right thing by inspecting the sheds. I always look for the eye caps.