Design features and surgical use of a cannulated extrusion needle

A cannulated extrusion needle was designed as a modification of the standard 20-gauge extrusion by including an inner 24-gauge flexible cannula that can be extended up to 18 mm beyond the metal tip. Indications for use of the instrument are reviewed along with selected case histories demonstrating its use. The instrument is used primarily for internal subretinal fluid drainage in eyes with complex retinal detachments caused by proliferative vitreoretinopathy. The flexible cannula is guided into the subretinal space through an open peripheral retinal break and the subretinal fluid is evacuated during a simultaneous fluid/air exchange. The positive pressure of the automated air pump creates a pressure gradient sufficient to achieve passive egress of subretinal fluid through the cannula. Active suction is avoided because of the risk of posterior retinal incarceration into the cannula tip. In addition, the cannula can be used to remove hemorrhage, gas, or silicone oil in the subretinal space.