Vision-and-Force-Based Compliance Control for a Posterior Segment Ophthalmic Surgical Robot

In ophthalmic surgery, particularly in procedures involving the posterior segment, clinicians face significant challenges in maintaining precise control of hand-held instruments without damaging the fundus tissue. Typical targets of this type of surgery are the internal limiting membrane (ILM) and the epiretinal membrane (ERM) which have an average thickness of only 60 $\mu \rm{m}$ and 2 $\mu \rm{m}$ , respectively, making it challenging, even for experienced clinicians utilising dedicated ophthalmic surgical robots, to peel these delicate membranes successfully without damaging the healthy tissue. Minimal intra-operative motion errors when driving both hand-held and robotic-assisted surgical tools may result in significant stress on the delicate tissue of the fundus, potentially causing irreversible damage to the eye. To address these issues, this work proposes an intra-operative vision-and-force-based compliance control method for a posterior segment ophthalmic surgical robot. This method aims to achieve compliance control of the surgical instrument in contact with the tissue to minimise the risk of tissue damage. In this work we demonstrate that we can achieve a maximum motion error for the end effector (EE) of our ophthalmic robot of just 8 $\mu \rm{m}$ , resulting in a 64 $\%$ increase in motion accuracy compared to our previous work where the system was firstly introduced. The results of the proposed compliance control demonstrate consistent performance in the force range of 40 $\rm{mN}$ during membrane tearing.