The normal lens of the eye is like a grape, having an outer skin and an inner gel-like material. When a cataract forms, the material inside the lens (nucleus) turns cloudy and interferes with good vision. Cataract surgery removes the cloudy lens and replaces it with a clear artifical lens (intraocular lens - IOL) implant.
During cataract surgery, the fine skin (posterior capsule) of the lens is left in place to support the intraocular lens implant. In some cases, through a normal process of cell regeneration, this capsule may turn cloudy forming a "secondary" cataract. The cloudy capsule interferes with good vision in a similar way a cloudy cataract lens blocks good vision. When this clouding develops, the YAG laser can be used to create an opening in the capsule and a clear path for light to enter the eye. This outpatient procedure is called Posterior Capsulotomy or Laser Posterior Capsulotomy. With this procedure, vision can be restored quickly and painlessly.