Halloween Contacts  can be the icing on the cake to a great costume. From zombie lenses to cat eyes, hypnotic eyes that glow in the dark to spooky flames or a clock face, there are many ways to add some extra horror to your outfit. However, they should be worn with caution.

Non-prescription decorative (colored) lenses can cut, scratch and injure your eye if they don’t fit properly. According to the American Academy of Ophthalmology (AAO), these ill-fitting contact lenses can cause corneal ulcers and a painful, potentially blinding bacterial infection called keratitis. They also tend to let less oxygen through the eye, since the paints and pigments used to add color make them thicker and less breathable than prescription lenses.

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AAO warns that you should only purchase these types of Halloween-colored lenses from reputable retailers and suppliers who adhere to strict safety standards. Never buy them from pop-up Halloween stores or other non-regulated vendors, who may not be FDA-approved. It is also illegal to sell them without a valid prescription in the United States.

You can find these types of lenses at e-commerce contact lens sites, at brick and mortar retail stores that carry cosmetic contacts, or at the offices of some eye care professionals. When buying them, look for a safe, reputable brand and read the instructions carefully. It’s also important to wash your hands with soap and water before touching the lens, and to never sleep or nap while wearing them, because your eyes need a continuous supply of oxygen to function properly.