Thanks guys for the responses. I was also thinking a vet check should be in order. The problem is that they live in a fairly remote place and Mandy is very aggressive. We've never understood why she is like this but she has always been like this. They were looking for a kitten and I had heard through the grapevine that a litter had been born in a nearby native reservation. They went to see the kittens and brought home Mandy at about 7 weeks of age. As she grew, she began to display really aggressive behaviour and it never went away. She is good with John, the husband and will allow him to handle her and love her but even then, she will slash at him and hiss if he holds her for too long or whatever. Cathy, his wife can get away with petting her and even picking her up for a few seconds but then watch out! Mandy freaks out and let's her have it. Totally bizarre. And as it turned out, I later spoke with the woman who owned the cat that gave birth to Mandy and the other kittens. I told her that Mandy was very different and also quite aggressive. She said "ya, that whole litter was like that, it was a bad batch". I was kind of stunned. It was as if we were talking about a batch of cookies!
Anyway, they used to ask us to petsit for them when they went away as we used to be neighbours and it was always a bit scary. My husband and I would take care of the goats, chickens and then feed the cats. By the time we were ready to head out, Mandy would get her back up and literally start stalking us and my husband would say "quick, you leave, I'll cover you!" LOL and then as soon as I was out, she'd make a beeline for him and he'd just get out in time. It was crazy.
She also terrorizes the other cat, a senior manx female who was with them for years before Mandy came along. And then the manx would come over to our house and take it out on our cat Sneakers (our only 'outdoor' girl). It was awful but then we moved and that at least solved our problem.
They have since relocated and for whatever reason, Mandy isn't attacking Hibou, the manx as much anymore but she does on occasion.
It would be very interesting to find out if there was some kind of connection between her unexplained aggressiveness and her eye?!?
I know that they will probably not opt to take her to a vet because the last time they did, Mandy scratched the vet in the face and made her bleed.
I'll maybe google it some more and see if I can find out anything else. It might be worth it to bring her in, get her sedated and have a full and complete workup done on her. However, they aren't really the type of folk who take pets to the vet unless it's an emergency. But, if I can convince them that it might be, maybe they will.