While they may be the perfect finishing touch on a costume, non-prescription cosmetic contact lenses can wreak havoc on your vision.

Below are four ways that over-the-counter decorative contact lenses can seriously harm your eyes:
1. Scratches

Conjunctivitis
Over-the-counter lenses are not fitted and sized for the person wearing the contacts, so they can easily scrape the outer layer of the eye. The resulting corneal abrasions can cause redness, light sensitivity, discharge, pain, plus the feeling that something is lodged in the eye.
2. Sores
Costume contact lenses can literally create an eye sore called a corneal ulcer, with symptoms similar to corneal abrasions. The ulcers sometimes appear as a white dot on the iris, the colored part of the eye, and may require treatment with medicated eye drops. When the ulcers heal, they can scar over and permanently and adversely affect vision.
3. Infections
Both corneal abrasions and ulcers create openings in the eye, making them more vulnerable to bacteria, viruses and amoebas. All of these organisms can cause serious eye infections known as keratitis. A 2011 study found that wearing cosmetic contact lenses increased the risk of keratitis by more than 16 times. Some infections, such as herpes simplex, can be recurring and difficult to eradicate, while a number of bacteria have become resistant to common antibiotic eye drops.
4. Blindness
In the most extreme cases, complications from wearing costume contact lenses may end in blindness or require surgery. For instance, extensive scarring from an infection can distort the cornea or make it opaque, requiring a corneal transplant to restore vision.