Black sclera contacts are safe only if they are treated as medical devices rather than toys. In the United States, it is illegal to sell any contact lenses, including costume or "plano" lenses with no vision correction, without a valid prescription from an eye doctor.

To wear them safely, you must consider the following:

1. Professional Fitting - Because these lenses are so large, an eye doctor must measure your eye to ensure the lens doesn't cut off oxygen or scratch your cornea.
2. FDA Approval - Only purchase lenses from reputable retailers that sell FDA-approved brands. Cheap, "street-market" lenses may contain toxic dyes or lead.
3. Hygiene - Because they cover so much of the eye, keeping them sterile is vital. Always wash your hands and use fresh multipurpose solution for cleaning.

No, you should never sleep in black sclera contact lenses. Because these lenses cover almost the entire surface of the eye and are thicker than standard contacts, they significantly reduce the amount of oxygen that reaches your cornea. Sleeping in them, even for a short nap, can lead to serious complications such as corneal swelling, severe infections, or permanent vision damage. Due to their size and the way they rest on the eye, most doctors recommend wearing them for no more than 6 to 8 hours at a time during the day.