This looks to me to be outside the
eye itself, rather than
on the nictitating membrane, (
on the eye-corner) where "Cherry Eye" occurs.
I might be wrong, but it's possible this is an abscess.Although some abscesses CAN be treated at home, I think by far the best thing to do is to take him to the vet as soon as possible. He may need antibiotics. If it is an abscess it will have to be drained fully before any healing takes place, and you do NOT want any infection to spread.