Surgical forces and tactile perception during retinal microsurgery

Abstract

purpose: Vitreoretinal surgery involves the manipulation of delicate retinal membranes with a required surgical accuracy often on the order of tens of macrons, a scale at or near the limit of human positional ability. In addition. forces imposed by the tissue on the surgical tool arc exceedingly small. Here we investigate the magnitude of forces generated during retinal surgery in cadaveric porcine eyes and compare the results with the magnitude of forces discernable by retinal surgeons. This data will be used as a design guideline for robotic surgical augmentation systems currently under development. Methods: The study was performed in two phases. First, retinal surgeons manipulated the retina of porcine cadaver eyes with a calibrated 1-axis force sensing retinal pick while data was simultaneously recorded In the second phase, blindfolded subjects held the pick and were instructed to press a button whenever an "event" was felt. Events were generated by slowly tapping the end of the pick with varying force while both the magnitudes of forces applied and the responses of the subjects were recorded. The magnitudes of forces generated during retinal surgery were then compared with those that could be discerned by the subjects. Results: Roughly 75% of all forces measured during retinal microsurgery were found to be less than 7.5 mN in magnitude, however, only 19.3 ± 8.1% (N=492) of events generated at this level could be fell by the subjects. Conclusions: The results of this study indicate that a majority of retinal surgery is probably performed without the surgeon being able to "feel" interactions between retinal tissue and live surgical tool. Prior studies have indicated that relying on visual feedback alone increases the length of manual manipulation tasks and red aces task accuracy. The lack of tactile sensation during retinal surgery similarly could adversely affect surgical outcome.