Fig. 6. Injection of gas into the vitreous base, which is a complication of pneumatic retinopexy. A. Donut sign when gas encircles the lens posteriorly. B. Sausage sign when gas partially encircles the lens posteriorly. In both cases the gas bubble is immobile and cannot be freely positioned in the vitreous cavity as desired. (From Wendel R: Pneumatic Retinopexy, p 94. Des Plaines, IL, Greenwood Publishing Co, 1989.)