The investigators will develop a new device for the precise and convenient measurement of eye movements. The device is based on the existing and widely-used wired scleral search coil technique, in which an annular contact lens with a small coil of wire is placed on the eye, and its orientation determined from the magnitude of the current induced in the coil by external magnetic fields. The new device uses a similar scleral contact lens on the eye, but the new lens contains three resonant coils, and has no wires leading from these coils to the associated electronics. A small set of transmitter/receiver coils placed near the eye generates magnetic fields that induce current in the eye-mounted coils, and in turn detect re-radiated energy from the resonant eye coils. The orientation of the lens and coils is determined from the magnitudes of the received signals. Development of the new device involves the fabrication of three coils on a single lens, resonant at three different frequencies, and implementation of associated signal processing algorithms for measuring the signals radiated by the coils and computing coil (eye) orientation.
This new method retains the conventional wired coil's benefits of high resolution and accuracy, large range of movement, and complete three-dimensional measurement of orientation. The largest drawback of the conventional system is the wires that lead from the eye coils to the signal processing electronics. By eliminating these wires, several very significant advantages result. Subject comfort is greatly increased, as the external wiring leading from the eye often irritates the eyelid and causes annoying stimulation of the eyelashes. A greater range of experiments can be performed, since the placement of the head within the external magnetic fields becomes less restrictive; head-free experiments, such as those involving locomotion and self-generated movements become much more practical. Perhaps most importantly, breakage of the external wiring (the most common source of failure in current systems) is avoided. The "wireless" measurement system will be of tremendous benefit to both the research and the clinical communities. In particular, vestibular and oculomotor patients should tolerate the new coils much better than existing ones, allowing easier and more convenient recording of precise eye movements in a larger segment of this population, for whom the conventional coils are often intimidating and uncomfortable.
