Electrical Bio-Impedance Proximity Sensing for Vitreo-Retinal Micro-Surgery

Retinal vein occlusion is a widespread eye vascular disease leading to vision loss because of clots obstructing a retinal vessel. Recent research investigated retinal vein cannulation, a promising treatment in which a microneedle injects a thrombolytic agent inside the clotted vessel. During this surgical procedure, the surgeon only relies on a microscope, looking through the patient eye's lens. Such visual feedback gives poor depth perception, with a risk to inject the agent underneath the retina. Such situation endangers the patient's eyesight and is to be avoided. This letter explores bio-impedance as a means to estimate the proximity between an insulated electrode and a retinal vessel. Experiments on five ex-vivo pig eyes showed that the impedance phase decreases as the electrode tip approaches the retinal vessel. Specific patterns in the impedance magnitude were detected. A dedicated algorithm showed 98 \% sensitivity and 100 \% specificity at a distance of 775 275 μm away from the retinal vessels. Knowledge of the proximity can help the surgeon prevent damaging fragile retinal structures during retinal surgeries such as cannulation and scar tissue peeling. A minimally-invasive measurement principle of this technique is demonstrated on an ex-vivo pig head to show the feasibility of such technique in more realistic conditions.