I think we're talking about two different things and at vastly different magnitudes. Being inside doesn't make your eyes worse because of like... the air in there. Or a roof. It's because wile you're in there your eyes aren't ever focusing on something far away. And it doesn't happen overnight. It's over the course of tens of thousands of "missed outdoor hours". If you stared into an abyss with nothing distant to focus on over tens of thousands of hours, it'd be the same problem. It's not because it's dark. It's because it's an abyss. When he was warning about "too long" into the abyss, it's tens of thousands of hours **(which displace outdoor time)**. You can look into the abyss a little bit. Sometimes. As a treat. Just not for too long.