When cataracts are removed using the most up-to-date methods (extracapsular extraction or phacoemulcification), a thin membrane is left intact behind the lens implant, or behind the pupil if no lens implant is used. This membrane is usually the back portion of the capsule of the natural lens. During cataract surgery the front portion of the capsule, as well as the cloudy substance within the capsule is removed. With time, cells may grow over this membrane and make it hazy. This condition is referred to as posterior capsulotomy. An option to treat this condition is to use a YAG laser to create an opening in the cloudy membrane.