i dont know if the author has made it official, but maybe stargardt disease, since he was born seeing and gradually lost his sight? but also visually he also looks to have cataracts. but the parts where he can see the outline of chinatsu dont make much sense with him being completely blind, but i assumed thats just yaoi logic/romanticizing lol. id love to hear your guess from your research!
Wow, I've never thought to look through the stargardt disease before (This is actually my first time finding out about it). Thank you so much for that lol. So, I'm actually helping my friends with one of their (summer) school projects (a story about a certain topic). They were told to make a story about a character with a vision impairments/problems (could be any genre). They chose romance (so, because of that, I remembered this manga, so I asked if what type of vision impairment Kasumi has, so here we are lol.) I reread it just to know for sure...My first thought? or suspicions is that Kasumi has a certain type of light perception blindness?? I'm not really sure about it, but because due to the light (in that part where Kasumi saw Chinatsu's shadow/outline?) it kinda has a match to it. I think, that was it and that was it lead me to cataracts lol. My first thought was the L.P.B Though, I think stargardt disease makes sense too, like literally. Thank you so muchhhhieee

What type of vision impairment (blindness condition or so) does Kasumi have? I've been trying to study about it, just wanted to be sure if I somehow got it right...idk