Are black sclera contacts bad for your eyes?

So i hear that those circle lenses are bad for your eyes, and my mind has the idea that circle lenses are pretty similar to sclera contacts. So i'm wondering: Are black sclera lenses bad for your eyes?

Circle lenses are nothing like sclera lenses.

Sclera lenses can't be worn for more than a few minutes usually. They are uncomfortable and block almost all oxygen from getting to your eyes. They are meant for doing a movie scene, then removed. You can bet the actors don't keep them on very long. Ever notice, you never see anyone wearing them in real life?