Adaptive canceling of physiological tremor for improved precision in microsurgery.

Physiological hand tremor impedes microsurgery. We present both a novel adaptive algorithm for tremor estimation and a new technique for active real-time canceling of physiological tremor. Tremor is modeled online using the weighted-frequency Fourier linear combiner (WFLC). This adaptive algorithm models tremor as a modulating sinusoid, and tracks its frequency, amplitude, and phase. Piezoelectric actuators move the surgical instrument tip in opposition to the motion of tremor, effectively subtracting the tremor from the total motion. We demonstrate the technique in one dimension using a cantilever apparatus as a benchtop simulation of the surgical instrument. Actual hand motion, prerecorded during simulated surgery, is used as input. In 25 tests, WFLC tremor compensation reduces the rms tip motion in the 6-16 Hz tremor band by 67%, and reduces the rms error with respect to an a posteriori estimate of voluntary motion by 30%. The technique can be implemented in a hand-held microsurgical instrument.

A flexible infusion micro-cannula for subretinal surgery.

Injection of fluids or drugs into the subretinal space is often necessary during subretinal surgery. The authors have developed a flexible micro-cannula for subretinal surgery that can be used for submacular injection of drugs or for atraumatic hydrodissection of the retina. The novel features of the soft tip include reduced diameter (200 microns), increased length, and material selection for resistance to tip buckling. The authors have used this cannula following pars plana vitrectomy for 14 patients with subfoveal choroidal neovascularization secondary to age-related macular degeneration (13 patients) and angioid streaks (1 patient). The cannula creates a relatively atraumatic retinotomy and allows an efficient, controlled injection of subretinal fluid. This micro-cannula seems to be a valuable tool for the subretinal infusion of fluids or drugs.

Quantitative measurement of the effects of caffeine and propranolol on surgeon hand tremor.

OBJECTIVE: To quantitatively measure the effects of caffeine and propranolol, a nonselective beta-blocking agent, on surgeon hand tremor during simulated vitreoretinal microsurgery. METHODS: Seventeen ophthalmic surgeons were tested on 3 separate days. On each day, subjects ingested 200 mg of caffeine, 10 mg of propranolol hydrochloride, or gelatin placebo. The drugs were administered as part of a double-masked, placebo-controlled trial. Hand tremor was measured using the Microsurgery Advanced Design Laboratory Stability, Activation, and Maneuverability tester (MADSAM), a high-resolution, noncontact position tracking system. RESULTS: The average percent magnitude changes from baseline tremor measurements were +15%, +31%, and -22% for placebo, caffeine, and propranolol groups, respectively. Analysis of variance techniques accounting for effects of individuals, drugs, and day order demonstrated that only drug effects on percent magnitude change of tremor were statistically significant (P = .01, F test). Detailed comparisons of the 2 drug groups with the placebo group revealed that, after adjusting for individual and order effects, only the mean decrease in tremor due to ingestion of propranolol was a statistically significant trend (P = .03, F test). Although caffeine caused a larger mean increase in percent magnitude change in tremor than placebo, this trend was not statistically significant (P = .34, F test). The evaluation of systemic physiologic measurements showed that there were statistically significant drug effects on percent change in systolic (P < .001, F test) and diastolic (P = .002, F test) blood pressure and pulse rate (P = .002, F test). Individual and day order effects were not significant. No adverse side effects were observed or reported in our test subjects. CONCLUSION: Physiologic surgeon hand tremor can be decreased by the oral intake of a low dose of propranolol.

A fiberoptic pick-manipulator for vitreoretinal surgery.

We have developed a new multifunction instrument for use during bimanual vitreoretinal surgery. The pick-manipulator provides the functions of a vitreoretinal pick, fiberoptic illumination, bipolar diathermy, and irrigation-aspiration of fluids and tissues in a single 19- or 20-gauge instrument.