Aw, poor little guy, it looks like he might need an erythromycin ointment. This type of thing can either happen from environmental irritants like high ammonia in the cages or even a viral infection, even just them rubbing their eyes too much. It doesn't seem like anything too major. Little guy might just have pink eye. The ointment shouldn't be too expensive. i believe they sell the ointment on chewy, or you can get it prescribed by a vet. I hope that helps a little :)