Eye matter can be a problem in big-eyed, short-nosed cats - breeds like the Persian that have that "mushed-in" look to their faces. The large eye openings and the small distance from the tear ducts to the nose in these cats create an area for more tearing to occur than usual. Rather than pooling into tear ducts, the tears spill over the lower eyelids. Once the tears come in contact with air, they are "oxidized" and turn brown, staining the area below the eyes and creating a glue-like substance that needs to be cleaned out to keep the area healthy and the cat comfortable.
To clean the eyes use a soft washcloth or a cotton square dipped in tepid water. Hold your cat's head and wipe the damp cloth gently across her lower eyelid. Be careful not to rub the eyeball directly. Let the moisture soften the eye matter and then go back and wipe again. Make sure you use a fresh section of the cloth each time.