A Membrane-Potentiometer-Based Palpation Position Sensor Suitable for Ophthalmic Anesthesia Training

To administer ophthalmic anesthesia, before injecting the anesthetic, it is essential to palpate, sense and ensure that the point of injection is correct. Hence, a training system for ophthalmic anaesthesia must include the features of assessing whether a trainee had performed palpation correctly and had inserted the needle at the appropriate position. In this paper, a system that uses a flexible membrane potentiometer for location sensing and a load-cell for sensing the palpation force is proposed to assess palpation. A modified successive approximation register (SAR) based digital converter functions as a simple analog to digital converter for converting the voltage output of the load cell. The converter additionally serves as a direct resistance to digital converter to measure the position indicated by a flexible membrane potentiometer. A method of computation that provides a palpation safety score, presented here, helps a trainee to review the training session in the training mode and assists the instructor to evaluate a trainee in the assessment mode. A prototype unit built and tested validates the presented technique. The location sensor of the prototype possesses a worst-case error of 0.8%, and the force sensor is found to have a worst-case error of 0.7 %.