The system comprises two major parts: magnetic field driver circuitry and signal demodulation circuitry, as shown in Fig. 1A–D. It records data from up to twelve scleral search coils. The system’s field coils refer to the coil frame itself, where each field coil pair, +X/−X (front/back), +Y/−Y (left/right), and +Z/−Z (up/down), are wired in pairs to make up the three orthogonal magnetic fields, X, Y and Z (following the right-hand rule). Each magnetic field oscillates at a unique frequency. Each field induces a voltage on each scleral coil. The three signals demodulated from each coil are proportional to the cosine of the angle between the scleral coil’s axis and the axes of each of the three field coils. With a set of two coils orthogonally attached to the sclera, the 3D VOR can be recorded and analyzed with 3D rotational kinematics equations described by Haslwanter and Migliaccio [23 (link)], [24 ].