Piper when he first came
I remember the health condition of Piper when he first came to our home. The kind woman who gave him and Parker his one-eyed brother to us told us that he was still on a regime and we should crush a quarter of an anti-biotic tablet and mix the tablet into his food. Piper sneezed quite a lot. His feces were somewhat watery. And while he and Parker were siblings of the same litter, it didn't look it because Piper were (and still is) much smaller in size. It was after a couple of months of good care that the sneezes stopped, the feces became solid, and the very discernible spine became padded by some flesh.
Piper goes on to become the brave, happy and plump little furry thing he is today, but he must have been much badly attacked by viruses to start with, thus his complete loss of sight and his poor initial condition. That's why, as I said yesterday, you don't see any (or at least many) blind cats hanging around in the street. It would be extremely tough for them to make it.