I. Introduction
Retinal microsurgery refers to a family of microsurgical procedures that treat retinal diseases such as retina detach-ment’ macular degeneration, diabetic retinopathy, epiretinal membrane, and retinal vein occlusion. Retinal microsurgery is one of the most technically challenging and high-consequence surgical disciplines. In the operating room, a surgical microscope is positioned above the patient's eye to provide magnified visualization of the posterior of the eye, as shown in Fig. 1. Small instruments, e.g., 23 Ga with 0.65 mm diameter, are inserted through trocars on the sclera to operate at the back of the eye. The surgeon needs to control the instrument motion in a very fine and precise manner to handle the delicate eye tissue. Due to the trocar constraint at the sclerotomy, the instrument motion is coupled with the eye movement. If the surgeon intends to keep the patient's eye still, only three rotational degrees of freedom (DOF) about the sclerotomy and one translational DOF along the instrument axis are allowed. This concept is termed as remote center-of-motion (RCM) in robotics, devised by Taylor et al. [1]. The lateral translation of the tool will move the patient's eye, causing change of the view in the microscope and possibly relative motion between the instrument and the retina, which is potentially risky when the instrument tip is close to the retina. This constraint limits not only the instrument workspace inside the patient's eye, but also the orientation of the instrument at a given position.
Retinal microsurgery: (a) Position of the patient and the lead surgeon in the operating room. (b) The layout of the surgical instruments in the eye during ERM peeling. A straight forceps tool is used to perform ERM peeling.