The vitrectomy process begins with a careful evaluation of the patient's eye condition and identifying the cause of the vision problem. The surgery is usually performed under local anesthesia with sedation or under general anesthesia in some cases. The surgeon makes several small incisions (typically three incisions, each less than half a millimeter wide) in the white part of the eye (sclera). Very fine surgical instruments are inserted through these incisions, including a cutting and suction tool (vitrector) to remove the vitreous, a light source to see inside the eye, and another instrument to inject fluid to maintain eye pressure and shape during surgery. After removing the vitreous, the surgeon addresses the underlying retinal issue, such as removing hemorrhage or scar tissue, repairing a retinal detachment using laser or cryotherapy, or closing holes in the retina. At the end of the surgery, the cavity may be filled with sterile saline solution, a gas or air bubble, or silicone oil to help keep the retina in place during the healing period. The small incisions are closed with stitches if necessary, but they are often self-sealing. A patch or shield is placed over the eye after surgery.