Ophthalmic viscosurgical devices (OVDs) are a class of clear gel-like material used in eye surgery to maintain the volume and shape of the anterior chamber of the eye, and protect the intraocular tissues during the procedure. They were originally called viscoelastic substances, or just viscoelastics. Their consistency allows the surgical instruments to move through them, but when there is low shear stress they do not flow, and retain their shape, preventing collapse of the anterior chamber. OVDs are available in several formulations which may be combined or used individually as best suits the procedure, and are introduced into the anterior chamber at the start of the procedure, and removed at the end. Their tendency to remain coherent helps with removal,[1] as the cohesive variants tend to be drawn into the aspiration orifice without breaking up.