Nonprescription contact lenses may pose a danger to eyesight. Cosmetic contact lenses that change eye color or the eye's appearance are becoming increasingly popular among teens and young adults. These lenses, which can often be purchased on the Internet and in mall specialty shops, flea markets and gas stations without a doctor's prescription, may harm the eyes, says H. Dwight Cavanagh, M.D., editor of the journal Eye and Contact Lens. Ill-fitting over-the-counter contact lenses can rub a person's cornea, causing infection and damage that could lead to blindness. The lenses could also cause irreversible scarring, inflammation and even loss of the eye.