why do cats have a lined eyed?

I'm going to guess that you mean why do they have slitted irises? Only the small and primarily nocturnal cats have slitted irises, it is to help them see better in the dark for their hunting. Now, if you have ever seen a horse's eyes, they have kind of horizanally slitted irises, it is to help them see behind them. On the other hand, are you talking about the lines around the outside of their eyes that they say the Egyptians immitated with kohl? That's a tabby cat trait.