An optical sensing system has been developed using a pair of orthogonally placed position sensitive detectors (PSD) to track 3D displacement of a microsurgical instrument tip in real-time. An infrared (IR) diode is used to illuminate the workspace. A ball is attached to the tip of an intraocular shaft to reflect IR rays onto the PSDs. Instrument tip position is then calculated from the centroid positions of reflected IR light on the respective PSDs. The system can be used to assess the accuracy of hand-held microsurgical instruments and operator performance in micromanipulation tasks, such as microsurgeries. In order to eliminate inherent nonlinearity of the PSDs and lenses, calibration is performed using a feedforward neural network. After calibration, percentage RMS error is reduced from about 5.46 % to about 0.16%. The system RMS noise is about 0.7 µm. The sampling rate of the system is 250 Hz.

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This study examines micromanipulation accuracy in pointing and in tracing a circle, using a novel contact-free measurement system. Three groups of subjects enable us to investigate the influence of age and micromanipulation expertise. The results show that, for all groups of subjects, a 10x magnification increases accuracy, but larger magnification does not improve it further. Expertise leads to reduced error, and grip force does not affect accuracy in the magnified condition.

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