Here's the issue.
In addition to site swaps, most cat-to-cat introductions involve separated feedings. One cat has a tasty bowl of food on one side of a door, and the other cat has the same setup on the other side. Then the door is replaced with a baby gate covered by a sheet. Then the sheet is gone. In time, the two cats are eating right by each other. By using this method, you demonstrate with sight and smell that the other cat is no threat. Every meal goes smoothly, with no fights, so the cats have proof that the other cat is peaceful.
It's hard to do this with blind cats.
Lucy can't see that Troy isn't menacing her. That means she isn't secure enough to eat. And since she isn't secure, her body position isn't friendly. That means Troy doesn't feel secure enough to eat. When I tried these introductions, I ended up with two cats facing one another and doing really nothing at all.
So here's what I tried.
Lucy will lose her mind for catnip. She'd rather have that above any other thing, even if it means she'll be attacked. When it comes to the herb, she doesn't care.
So I put her scratching post right by the baby gate, and I lured her to play with some catnip. She ran right up to roll and scratch and lick. Troy watched that from a distance, and I saw his body posture relax. She looked playful, not harmful. He could see her and smell her, and she ignored him. That made him a little more comfortable.
After a few sessions of this (like two), Troy started cheeping at Lucy during her play sessions. He's a friendly, kind cat and he wanted to join in her fun. He walked up to the gate, chirping and cheeping. She could hear that, and since those were friendly noises, she accepted them. She started to accept him. In time, they could touch noses through the gate.
After about a week of supervised feedings/playtime and site swaps, Troy was ready to have face-to-face meets. And he's done extraordinarily well. He's even won over Maggie, who typically hates everyone.
They're not exactly snuggling, but they have relaxed body postures. And they're in the same room. That's pretty good for a first meeting.
But Lucy needs more time. She isn't quite sure what this new cat is all about, and she's not sure she won't be harmed. She's not attacking Troy, but she is choosing to hiss at him just a little bit, especially if he gets too close.
I work hard to transfer scents. I pet him and then her. I swap out their bedding. I swap out their food. I say her name while petting him. I say his name while petting her. Every day she gets better.
But clearly, when it comes to blind cat introductions, the emphasis must be on introductions that come with sound and with scent. Those gated feedings just do not work on these sightless guys. By using toys, treats and scent, those introductions can go a little more smoothly.