A fiberscope for conducting observations in a region ordinarily filled with an opaque liquid, particularly, inside blood vessels or the heart. A recess is provided at a front end of a cover tube for accommodating a front end portion of an image fiber and a bundle of illuminating light transmitting optical...http://www.google.co.uk/patents/US4569335?utm_source=gb-gplus-sharePatent US4569335 - Fiberscope
