There have been many advances in contact lenses over the years. One of these advances involves the contact lens' ability to transmit oxygen. The more oxygen a contact lens can transmit, the healthier it is for the eye. These lenses are generally a silicone based lens. Basically, it is always safer to take a contact lens out than to sleep in it. Many infections that occur due to contact lens wear involve sleeping in the lenses. Even though I don't condone sleeping in the lenses, if you're going to do this, it is better to do this with a contact lens that transmits a significantly higher amount of oxygen.