What are eye movements?
The fovea is the central part of the primate retina that contains an area of densely packed photoreceptor cells. As a consequence, visual acuity is highest in the fovea and progressively decreases towards more peripheral parts of the retina. In order to explore a visual scene, the eyes have to move in such a way as to bring the image of an object of interest onto the fovea and to maintain it stable.
What is defined as eye movement is actually a rotation of the eyeball within the orbit. This rotation is made possible by the action of six extraocular muscles.
Medial and lateral recti control eye rotation in the horizontal plane, superior and inferior recti control rotation in the vertical plane and superior and inferior obliques are responsible for torsional movements.