A new method for eye location tracking

A standard scleral search coil (SSC) system is supplied with a single three-axial transmitter (or with a triad of transmitters) and the direct magnetic coupling between the transmitting coils and the SSC is used for computing the eye location. The SSC's orientation components measured by the SSC system are involved in the location-tracking algorithm as well. The suggested method differs from traditional ones where the eye location is computed indirectly, relative to the measured location and orientation of a transitional three-axial magnetic sensor attached to the subject's head. The new method eliminates systematic errors caused by inaccurate situating the transitional sensor relative to the eye. It also eliminates systematic errors caused by imperfect orthogonality of the transitional sensor. It is found that an accurate location tracking with a single transmitter is possible only if orientation freedom of the eye is limited. To track the eye location with no orientation limitations, a triad of transmitters is employed. The resulting accuracy can be as good as +/- 1 mm (in a 200-Hz bandwidth) over a relatively large (0.5 x 0.5 x 0.5 m) operating region in the center of a 1 x 1 x 1 m SSC system. The analytical results obtained are confirmed with the help of computer simulations.