Force-Sensing Microneedle for Assisted Retinal Vein Cannulation*

Retinal vein cannulation (RVC) is a challenging procedure proposed for drug delivery into the very small retinal veins. The available glass cannulas for this procedure are both hard to visualize and fragile thereby limiting the feasibility of both robot-assisted and manual RVC approaches. In this study, we develop and test a new force-sensing RVC instrument that can be easily integrated with the existing manual and robotic devices. The tool enables (1) the measurement of the forces required for puncturing retinal veins in vivo and (2) an assistive method to inform the operator of the needle piercing the vessel wall. The fiber Bragg grating based sensor can be inserted into the eye through a small (∅ 0.9 mm) opening and provides a quantitative assessment at the tool tip with a resolution smaller than 0.25 mN. Assessment of forces during vessel penetration in the chorioallantoic membranes of chicken embryos have revealed a consistent sharp drop in tool tip force upon vessel puncture that has been used as a signature to provide auditory feedback to the user to stop needle advancement and begin drug delivery.