Head-mounting Surgical Robots for Passive Motion Compensation

Many up-and-coming therapeutic protocols in ophthal- mology are technically difficult, near/beyond the limits of human ability, and are being attempted by only a few surgeons. For example, subretinal injection of stem cells or gene therapies requires placement of a fine cannula in the subretinal space, holding that position steady for ∼90 s to inject a bleb of fluid. Surgeon hand tremor places a limit on achievable precision. A wide variety of robot-assisted surgical systems have been proposed to improve the precision of eye surgery [1]. However, there has not been much consideration of patient head motion, which is common among patients undergoing eye surgery under monitored anesthesia, a.k.a. conscious sedation, which makes a patient calm and somewhat sleepy during a surgery, but the patient may still be awake. Head motion in this state is due to breathing, talking, snoring, and other (in)voluntary motions of the patient. Of the 16% of patients who snore under monitored anesthesia, half have sudden head movement during surgery [2]. Movement must be compensated by the surgeon, to the best of their ability, to avoid complications. Benchtop experiments with artificial or enucleated (i.e., ex vivo) eyes, which are typical in the development of robotic systems, do not capture the effect of patient motion. Limited in vivo studies in humans have placed the patient under general anesthesia [3], [4], which is not typical of eye surgery and results in reduced patient movement (the patient is still breathing, of course). Any clinical robotic system must deal with patient motion. Active compensation (i.e., closed-loop control) can involve sensing the force between the sur- gical instrument and the eye, or using visual-servoing techniques, or some combination of both [1]. Two groups (including ours) have developed compact telerobotic systems motivated by the prospect of mount- ing the robot directly to the patient’s head to passively compensate for patient motion [5], [6]. However, to date, neither has actually mounted their robot on a living human, let alone quantify the benefits of head mounting. Mounting a robot to a patient’s head is not a trivial task.