Oh no poor little guy. Did he maybe get stung or bit by some bug? Or is it swollen from an injury? Does he have a scratch on or near the eye? If it is from an injury then it's probably just bruised and it will heal on its own, but if its from a bite or sting, you might want to try a Benadryl to see if it helps the swelling go down. If your not sure if his eye is okay, maybe a call to,the vet, or a quick trip in to have it checked wouldn't hurt. I'm not sure about the drops, if they would help for this situation, but you could also,ask your vet this question. You could also try Polysporin eye drops or the cream if it was from an injury. Hope Tubby feels better soon. Keep us posted. Can you post a picture of his eye?