The Request:
The sadness is inevitable and he doesn't hide his disappointment. He knew what would be the most merciful choice but, as his father once was, he is not able to kill an innocent child. He would probably delegate to the mother the responsibility to raise this child and pray to the gods he can live at least a good life.
Sadness and concern take his soul completely. After this discovery, he would spend at least the next three nights rolling in the bed, first trying to understand what he did wrong to his innocent son to suffer like that; then, trying to forget how hard his son's life will be from now on. He doesn't even think about the possibility of getting rid of the child. Instead of it, he is entirely supportive and will try his best to make his son's life easiest as possible.
Of course, he is sad, but it's nothing that will consume him. After all, look at his little brother Ivar: two legs left and what he was able to face his entire family, fight his brothers, win battles and lead an army! Blindness is not a limitation: it is an obstacle to be surpassed and he will be by his son's side to whatever he needs in this direction.
He's sad but tries to keep the rationality and focus on what needs to be done to make his son's life easier but also does not make him entirely dependent on the others. He'll do as much as he can to raise his child as normal as possible, avoiding - on all the ways! - to make his disability a reason to spoil him.
It is not sadness. Frustration is the dominating feeling in his soul and even if he knows his son will be able to surpass this disability and that it could be a sign of the favor of the gods, he blames himself thinking that someway his child's disability must be connected to his own and it still makes him angry and frustrated that his child will face such a hard life as it was his own.