There are all kind's of congenital and genetic eye diseases and defect's. Were the parent's of the pup in question cerf'ed (or there are sometimes DNA test's for auto-recessive for some breed's in some places)? Breed and age? Check with your breed parent club for a better idea of what problem's the breed may be prone to as the specific problem (there can be many reason's for swelling of the optic nerve) and whether it is generally a congenital defect or genetic or whether it is something that can occur for other reason's.