I have 2 inside purebred cats that receive good care and nutrition. They both get black debris in the inner corners of their eyes. Could this be a parasite? I can wash it out with a cloth. It almost looks like an insect. The cats are completely inside cats and they do not have any indications of fleas or other problems.
In some cases this is the norm and there is not much you can do about it. If your vet checked out the eyes and found nothing wrong then I would just keep the area clean with warm water. vetcare