"U.S. Pat. No. 3,698,791 (Walchle et al.) describes a very thin, transparent microscope drape which includes a separately formed, optically transparent, distortion-free lens for viewing. [0007] In another familiar application, multi-lumen balloon catheters are utilized as dilatation devices for dilating a blood vessel, e.g. a coronary artery, or other body canal." . . . .