The Muscles of Eye Movement
When someone looks at you from across the room or when you look down toward your book the eye is in motion. This requires the use of several different muscles. Each muscle plays an important role in helping the eye to be able to move up, down, left and right. Your eye muscles may be small, but you should always remember that they are powerful too. They play just as important a role in your vision as do the various parts of the eye.
The Six Extraocular Muscles
There are six extraocular muscles which work together to move the eye. Each muscle is responsible for a primary type of eye movement and may also play secondary roles in other eye movements. Each muscle is involved in some fashion each and every time the eye moves. The six extraocular muscles are known as the medial rectus, the lateral rectus, the superior rectus, the inferior rectus, the superior oblique and the inferior oblique. All of these muscles form a cone like shape that starts at the back of the eye and that come to a point at a tendon called the annulus of zinn. The optic nerve travels through the middle of the muscle cone to transmit what you see to the brain.
Let’s look at each of the six muscles of the eye a little more closely to better understand the role that each plays in moving your eyes.
Medial Rectus- The medial rectus helps the pupil (or center) of the eye to move inward toward the nose. It is attached near the side of the eye on the inward side (closer to the nose).
Lateral Rectus- The lateral recurs is used when the pupil moves in an outward direction, away from the nose. This muscle attaches to the eye near the back of the eye on the outer side of the eye (closer to the side of the head).
Superior Rectus- The superior rectus moves the eye upward. This muscle attaches to the top of the eye and then moves directly back to the point of the cone shaped bundle of muscles known as the annulus of zinn.
Inferior Rectus- The inferior rectus moves the eye downward. It attaches to the eye at the bottom middle of the eye and then continues in a fairly straight path back to the annulus of zinn.
Superior Oblique- The superior oblique moves the top of the eye toward the nose. This muscle attaches to the eye at the top of the eye and proceeds toward the annulus of zinn by way of a small tendon known as the trochlea. The trochlea acts as a pulley and assists this muscle in moving the eye in the proper direction.
Inferior Oblique- The inferior oblique moves the top of the eye away from the nose. It is the only eye muscle that does not terminate in the annulus of zinn. It is located at the bottom of your eye.
How the Eyes Move
The muscles of your eye aren’t just there to provide movement to your eye. They also help to hold your eye in place and stabilize it when it is not in motion. Each of the muscles that move your eye have a resting position and when the eye is not in movement it will rest in its standard position. When it comes time for the eye to move some muscles will increase their activity while the activity of others will decrease. The eye has several primary motions. It can move the pupil toward the nose (adduction), laterally (abduction), up (elevation) or down (depression). When the top of the eye moves toward the nose it is known as intorsion and when the bottom of the eye moves away from the nose it is known as extorsion.
Together or Separately- Ductions, Versions and Vergences
As you know your eyes can move together or separately. If you are talking about one eye moving on its own this is known as a duction. When the eyes are both moving in the same direction it is known as a version. If both eyes are moving at the same time but in different directions it is known as a vergence. For example if you were to move both of your eyes to the right the movement would be considered a version. On the other hand if you look down at a book and focus on the pages your eyes would be moving in a vergence. These principles are in play each and every time that your eyes move.
The movement of your eyes might seem simple when you look up or down but it is actually a very complicated process that involves many small muscles known as the extraocular muscles.
It is always a good idea to consult with your eye doctor to discuss your options.
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