Coordination of Movement Between Both Eyes
Intermediate directions are controlled by simultaneous actions of multiple muscles. When one shifts the gaze horizontally, one eye will move laterally (toward the side) and the other will move medially (toward the midline). This may be neurally coordinated by the central nervous system, to make the eyes move together and almost involuntarily. This is a key factor in the study of squint, namely, the inability of the eyes to be directed to one point.
There are two main kinds of movement: conjugate movement (the eyes move in the same direction) and disjunctive (opposite directions). The former is typical when shifting gaze right or left, the latter is convergence of the two eyes on a near object. Disjunction can be performed voluntarily, but is usually triggered by the nearness of the target object. A "see-saw" movement, namely, one eye looking up and the other down, is possible, but not voluntarily; this effect is brought on by putting a prism in front of one eye, so the relevant image is apparently displaced. To avoid double vision from non-corresponding points, the eye with the prism must move up or down, following the image passing through the prism. Likewise conjugate torsion (rolling) on the anteroposterior axis (from the front to the back) can occur naturally, such as when one tips one's head to one shoulder; the torsion, in the opposite direction, keeps the image vertical.
The muscles show little inertia - a shutdown of one muscle is not due to checking of the antagonist, so the motion is not ballistic.
Read more about this topic: Muscles Of Orbit
Famous quotes containing the words movement and/or eyes:
“When delicate and feeling souls are separated, there is not a feature in the sky, not a movement of the elements, not an aspiration of the breeze, but hints some cause for a lover’s apprehension.”
—Richard Brinsley Sheridan (1751–1816)
“One is not idle because one is absorbed. There is both visible and invisible labor. To contemplate is to toil, to think is to do. The crossed arms work, the clasped hands act. The eyes upturned to Heaven are an act of creation.”
—Victor Hugo (1802–1885)