 Newer materials, such as silicone hydrogels, allow for even longer wear periods of up to 30 consecutive nights; these longer-wear lenses are often referred to as "continuous wear" (CW).EW and CW contact lenses can be worn overnight because of their high oxygen permeability.While awake, the eyes are mostly open, allowing oxygen from the air to dissolve into the tears and pass through the lens to the cornea.