If he is growing, he is eating and active. If he is eating and active, pain is low. It may look bad, but he is fine.
Pink eye in humans looks bad too, but we know it passes and is not a big deal. I am not saying this is conjunctivitis, I am just pointing out that as a species that relies primarily on vision, we are easily squicked out by eyes. Rabbits rely more heavily on smell and hearing than we do, so they often seem less distressed by eye issues. I would let him make weight as long as he seems to act about like the rest of the kits. If he is constantly huddled in a corner looking cold, with a hunched posture and shivering, then cull immediately. That is pain.