Ah oops. My answer is actually wrong because the concept of mine is the man was actually not cured and only realised it in the dark, while the real answer was that the man was actually cured but thought he wasn't in the dark.
So you could've given a
NO and some hints.
Anyways, you've already revealed the true answer so whatever.

Mine would explain how he would still want to suicide even if he passed any kind of light though, but he wouldn't be so suicidal if it was just night-blindness. :/ Perhaps he was really poor and paying that surgery already got him bankrupt? :V