He lost his right eye from smallpox, not in battle and was nicknamed Dokugan-ryu ( One-Eyed Dragon ).
His right eye was lost due to small pox and he was known as the one eyed dragon. 
mnli hypothesis: His right eye was lost due to small pox and he was known as the one eyed dragon.  premise: He lost his right eye from smallpox, not in battle and was nicknamed Dokugan-ryu ( One-Eyed Dragon ).