
I am assuming you are referring to prcd-PRA or another DNA testable recessive trait.
Really both parents should be DNA tested and their status known, but as long as one is DNA tested clear then pups will be fine. If the other parent is clear they will all be clear, if the other parent is a carrier, then half are likely to be carriers. If the other parent was an untested affected (I can't see anyone knowingly using an affected, unless it was to save a precious bloodline) then all the pups would still be fine but all carriers.
On the other hand if the parents are only eye tested, which is a clinical eye test, this can only show a dog as not being clinically affected, it does not mean they are genetically clear (they could still be a carrier, or even affected in breeds, like my own, where clinical signs appear late).