The function of the extraocular muscles, the theory of the coplanarity of the fixation planes

A theory of visuomotor kinematics is derived from evidence obtained by a video method that allows the eyes to gaze freely in any direction with the head stabilized in any position in space, allows the head to move freely while the eyes are stabilized in different gaze directions, and allows the eyes to move in sync with the head. Frame by frame analysis reveals no wheel-rotation (torsion) around the visual line in any gaze direction. There is dynamic rolling around the visual line during head tilt but no static counter-rolling when the head is held steady in any position. Lateral rotations are wheel-rotations around a vertical polar axes fixed in the eyes. Vertical rotations occur around collinear axes fixed in the orbits. Oblique rotations consist of successive arcs of longitude and latitude, which project as slopes (the tangent to a point on a curve). All eye movements are commutative. Head movements enable the eyes to fixate any point at any angle in 3-D space.ConclusionThe extraocular muscles are programmed by the brain to maintain the fixation planes of the two eyes coplanar in all stable head positions and in all gaze directions. The retinas are in dynamic equilibrium with the brain and with each other in all head positions. The extraocular muscles function to maintain conjugacy, retinal correspondence, and retinotopy. The retinas are oriented to the brain and not to the horizon.