A Novel Force-Sensing Instrument for Vitreoretinal Microsurgery

Abstract

Purpose: : Ophthalmologic surgery is technically demanding because of microscopic tissue dimensions, poor functional recovery after injury, and because many surgical maneuvers are below human tactile sensation. Injury to delicate ocular tissues may result from forces generated during a surgical maneuver that exceeds the tissue’s strength. Today’s surgical instruments, while highly sophisticated, do not provide physiological or interpretive information such as measuring tissue forces during surgery. The purpose of this study was to develop a force-sensing instrument that measures forces below tactile sensation during surgical maneuvers.

Methods: : Three 1 cm long, 160 µm diameter Fiber Bragg Grating strain sensors set 120^o apart were embedded longitudinally in a 0.5 mm diameter (25 gauge) pick that measures the transverse force in two degrees of freedom (DOF). The instrument was calibrated in an analytic balance by measuring the force generated when lifting a known weight. The chick chorioallantoic membrane (CAM) model (N=12), which contains two membranes, designated upper and lower, that mimic an epiretinal membrane and the retina, respectively, was used to model vitreoretinal surgery. All measured forces were recorded during simulated surgical maneuvers.

Results: : The force-sensing instrument measured forces with a resolution of 0.25 mN in 2 DOF. Using the CAM model, delamination of the upper membrane produced an average force of 2.8±0.21mN (range, 4.14-1.35mN). With delamination intended to rupture the lower membrane while pulling on the upper membrane to create tissue injury, the average force was 7.27±0.51mN (range, 5.09-9.20mN).

Conclusions: : Force-sensors integrated into microsurgical instruments are feasible and have the potential to improve vitreoretinal surgical success and minimize potential complications.

Keywords: vitreoretinal surgery