3-DOF Force-Sensing Micro-Forceps for Robot-Assisted Membrane Peeling: Intrinsic Actuation Force Modeling

Membrane peeling is a challenging procedure in retinal microsurgery, requiring careful manipulation of delicate tissues by using a micro-forceps and exerting very fine forces that are mostly imperceptible to the surgeon. Previously, we developed a micro-forceps with three integrated fiber Bragg grating (FBG) sensors to sense the lateral forces at the instrument's tip. However, importantly this architecture was insufficient to sense the tissue pulling forces along the forceps axis, which may be significant during membrane peeling. Our previous 3-DOF force sensing solutions developed for pick tools are not appropriate for forceps tools due to the motion and intrinsic forces that develop while opening/closing the forceps jaws. This paper presents a new design that adds another FBG attached to the forceps jaws to measure the axial loads. This involves not only the external tool-to-tissue interactions that we need to measure, but also the adverse effect of intrinsic actuation forces that arise due to the elastic deformation of jaws and friction. In this study, through experiments and finite element analyses, we model the intrinsic actuation force. We investigate the effect of the coefficient of friction and material type (stainless steel, titanium, nitinol) on this model. Then, the obtained model is used to separate the axial tool-to-tissue forces from the raw sensor measurements. Preliminary experiments and simulation results indicate that the developed linear model based on the actuation displacement is feasible to accurately predict the axial forces at the tool tip.

Vitrectomy for idiopathic epiretinal membrane in elderly patients: surgical outcomes and visual prognosis

PURPOSE

To evaluate the clinical course and visual prognosis of elderly patients over 75 years of age who underwent PPV and peeling of idiopathic ERM.

DESIGN

Retrospective case series.

METHODS

A retrospective chart review of patients that underwent vitrectomy for idiopathic ERM in two public hospitals. Twenty nine eyes of 29 patients 75 years and older who underwent PPV and ERM peeling were included in the study series. Patients with additional ocular vision-limiting conditions other than cataract were excluded. Main outcome measures included VA improvement, OCT changes and complications.

RESULTS

Mean patient age was 79.6 years, the highest in published literature. Mean change in VA was 0.23 logMAR units, and 65.5% patients gained 2 or more lines of vision. Eight of the 10 patients aged 80 years or older gained 2 lines or more. Fourteen patients (48.3%) achieved final VA of 20/40 or better, and only 2 (6.9%) had final VA of 20/200 or worse. Concurrent cataract extraction was performed in 73% of the phakic eyes, and at the end of the follow up 93% were pseudophakic. Complication rates were similar to those reported in the literature.

CONCLUSIONS

Pars plana vitrectomy with ERM peeling is safe and effective in restoring VA in elderly patients, and the results are comparable to those previously reported for younger patients with idiopathic ERM. Old age should not hinder surgery in patients with idiopathic ERM who seek to improve their vision and quality of life.