A surgical instrument in particular for eye surgery has a housing having a good surface for placement on the eye. A knife is held retracted within the housing under the bias of a torsion spring. An ultra-sonic transducer measures the thickness of the part of the eye local to the surface. A control system...http://www.google.ca/patents/US4637393?utm_source=gb-gplus-sharePatent US4637393 - Surgical instrument
