I feel horrible saying this, but it's prob a "fresh corpse", and it's not like someone will offer their loved ones corpse...
I had the exact same thought but I was trying to wrap by head around it by thinking abt the context they’ve given us in the story. so all we know about this procedure is that it’s extremely new and has only been performed successfully one time. maybe that one successful operation was done with a donation from a living person, so that’s why they can’t just use a corpse, because they don’t know if it would be successful with their current technology. Still not sure why they couldn’t find a more “disposable” person, especially when they have the influence to shut people up
As Lucas said, if the eyes are only damaged on the surface and can be fixed by someone else donating it, why are they not trying to find someone who’s actually dead and use it?? They took Paula and was ready to get rid of her since no one would look for her and there is no problem with this logic but finding another dead person or using the eyes of the previous killed maid is a no no? He is a fricking Count and has the money and power to do it so I really don’t understand why he’s suffering so much. I get that the author was trying to put angst and make the story more tragic but logically I can’t wrap my head around the idea that Lucas has to die for him to gain his eyesight back when he can clearly just get a surgery. The house is bad enough to kill people they picked out from streets but not enough to use their eyes? I wish the author came up with something else other than this idea since made a big plot hole in the story and the tragedy feels really forced when read.
Like I can’t even feel sad that he’s going to die cuz I doesn’t make sense