Eyes admit light from a limited range of directions, so it is important that an animal be able to redirect its gaze to examine its surroundings. This is achieved by movements of the body, the head, and usually the eyes as well. Animals also use vision to guide movements of the body, and one would like to understand the way in which visual sensory information is transformed into motor commands. The relative simplicity of ocular movements, as compared, for instance, to movements of the arm, makes them useful for the study of such sensorimotor transformations.

The angle over which an animal can sweep its direction of gaze by moving its eyes alone is called its oculomotor range. This varies from species to species. The oculomotor range of a cat is about 50°, and that of macaque monkeys and humans about 90°. Owls rotate their tubular eyes only about 3° in the orbits, but a very mobile head compensates for this. Chameleons can rotate their turret-like eyes independently. Invertebrates employ a variety of mechanisms to explore their visual environments. Compound eyes that are fixed to the exoskeleton are moved by head or body movements. Jumping spiders are able to move their retinas behind the fixed lenses of their ocelli, and certain copepods also have mobile ommatidia and secondary lenses that scan the image created by stationary optics at the body surface. Decapod crustaceans, such as lobsters and crabs, can move their stalked eyes in drifts, tremors, and saccades independently of head and body movements.