Eye Movements

AbstractA description of eye movements is presented in this chapter. In addition, models of the saccadic system and smooth pursuit system are also presented. Five different types of eye movements exist: saccades, smooth pursuit, vestibular ocular eye movements, optokinetic eye movements, and vergence eye movements. Saccades are a fast eye movement used to acquire a target by placing the image of the target on the fovea. Smooth pursuit is a slow eye movement used to track a target as it moves by keeping the target on the fovea. The vestibular ocular movement is used to keep the eyes on a target during brief head movements. The optokinetic eye movement is a combination of saccadic and slow eye movements that keeps a full‐field image stable on the retina during sustained head rotation. Each of these movements is a conjugate eye movement, that is, movements of both eyes together driven by a common neural source. A vergence movement is a nonconjugate eye movement allowing the eyes to track targets as they come closer or move farther away.The smooth pursuit system allows tracking of a slow‐moving target to maintain its position on the fovea. Models of the smooth pursuit have been developed using systems control theory, all involving a negative feedback control system that includes a time delay, controller, and plant in the forward loop with unity feedback. The oculomotor plant and saccade generator are the basic elements of the saccadic system. The oculomotor plant consists of three muscle pairs and the eyeball. The control of saccades is initiated by the superior colliculus (SC) and terminated by the cerebellar fastigial nucleus (FN), and involves a complex neural circuit in the mid brain. Both of these control models are for horizontal eye movements only.