July 31, 2015
This is a simple question, but one that can take some time to explore. There are two types of vitrectomies: anterior and pars planar. An anterior vitrectomy is typically performed during or after a cataract surgery in which the posterior capsule has torn and lens fragments have fallen into the anterior vitreous. If the posterior capsule is torn, then the anterior vitreous could prolapse through into the posterior chamber and maybe the anterior chamber.
Removal of this vitreous and the lens fragments is necessary to lower the risk of complications from the surgery, especially endophthalmitis.