Circle lenses are just like regular coloured contact lenses in that they do not allow as much oxygen to reach the iris as would without anything on the surface of the eye. This is where the Water Content of the lens becomes important. The water in the lenses is the carrier of oxygen, therefore the higher the water content, the more comfortable and safer to wear the lens is. Circle lenses should never be worn for more than 6-8 hours, nor can they replace your regular prescription contact lenses.
Any contact lens can damage your eyes if the proper steps aren't taken to prevent this. Contacts should never be worn if they are damaged, or if you've found they irritate your eyes. It is also important to properly store and clean contacts regularly. For more information on proper lens care you can visit this site, or see your optometrist.
If used with care, Geo Circle Lenses can provide the doe eyed look and still be just as safe and easy to use as regular colour contact lenses.