I’m assuming your talking about the piggy’s eye? Looks like pea eye to me
Sry it was very careless for me not to recommend seeing the vet, I wasn’t thinking before I wrote it.It could be the start of pea eye (the falling away from the lower eye lid), but it is not quite clear from the picture to me. Since I have no direct access to the guinea pig to have a closer look, I prefer to recommend to see a vet.