OCTOBER UPDATE:
Merlin is still around but he has been falling very often these last days, when I came home on Thursday he was under my bed, I put him back up on the cage and went to hang my jacket up, he fell in the meantime. Put him back up, he fell again... So I just had to check, and I think his other eye is gone too, he didn't react at all to my hand coming close on any side of his head. His second eye is probably still catching the light but he doesn't seem to see forms anymore. His head is still bent though, so that's due to his neck and not to being blind in one eye like the vet said.
I just think he's been falling so many times that he has multiple concussions now, poor boy
And despite all the protections under the cage, he has many times managed to fall beside them...
So these two last days have been spent pondering and trying solutions to prevent him from falling, and also making sure that if he should fall he'll land on the protections instead of on the hard floor. I've been sewing walls around the top of his cage so he won't fall on the backside when he climbs. He also has a ramp to climb up to Nova's cage (which was his too before, so he loves to be there) and his cage is side by side with hers instead of face to face. It doesn't matter so much anymore if he can see her or not, does it?... He gets more sun light and warmth from the new position and there is a small heater behind the cage so he can keep warm when he sleeps at the back. He is not allowed to climb up their tree over Nova's cage anymore though, this is too high and too risky so I've prevented his access there. He has had a towel stretched over the bottom of his cage since he moved for himself in June, and this is just wonderful, like a trampoline, doesn't matter if he falls, there is nothing hard under and it makes his cage very safe.
Despite all that, him being completely blind doesn't make it easy. He has to learn new routes and new places for things around when he was used to the former agencement. I had to rebuild his ramp when he started to climb ON the protections instead of them keeping him safe on the ramp. He is a quick learner though, and felt only once today. Of course, I'm home today, helping him to learn his new environment and I could pick him up when he moved to the wrong place. Hopefully he'll improve tomorrow again and be fine on his own on Monday!