No I don't know but I can tell you what happened to our dog. He was sluggish and I don't know why we took him to the eye doctor and he had glaucoma and that is very painful.
He was actually blind in that eye. The 2nd eye we kept the pressure under control with medication. This winter after several years he got a cataract in his 2nd eye and he was too old for surgery, but my vet says the surgery does not often work and they might get glaucoma and it again that is painful.
This winter he went blind but we still have to give him eye drops in both eyes so the pressure won't build up.
I hope you don't have this problem but because you said sluggish and red eye (I assume the white in his eye) I would advice you at least to get it checked soon.
We were in shock when it happened because it felt it happened overnight.