I agree with Jade on this one. Feline herpes is a chronic immune disease that doesn't ever go away, but is highly manageable. Because it is an immune disease, it can result in both chronic and from time to time flare ups of symptoms, particularly upper respiratory.with eye and nasal draining. Lysine does provide some immune system support when taken consistently, but it will not cure anything. It just helps boost you cat's own immune system a bit to help her shed other infections. If the black spot is not raised or large enough to affect her vision, I wouldn't be concerned about it. It is probably just some pigmentation which may be either fixed or floating. However, if you notice any swelling in that eye, then I would take her back to the vet for further treatment specific to the eye.
Did your vet stain the eye? Its possible, especially since its only 1 eye, that the cornea could have been scratched & then kitty rubbed it due to the irritation, it ended up with an ulcer.
Hi and welcome. Your vet is probably suspecting the runny eye is due to an underlying herpes condition (which is very common), thus, recommending the Lysine. The Lysine wasn't given to treat the black spot or the eye itself but rather to boost kittys immune system. It's probably not cataracts, especially given your cats age, however, the eye can have a cataract *appearance* (IMO) when affected by a herpes outbreak or the cat is simply ill.
Are you sure this black spot isn't just simply part of the coloring or is it new? Did your vet SEE the back spot? What did he say about it?