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| The Surgical Technologist | AUGUST 2017 352 A N A T O M Y Three pairs of extraocular muscles per eye are responsible for generating its movements. 2 They are: 1. L ateral rectus (LR) – outward movement Medial rectus (MR) – inward movement 2. Superior rectus (SR) – upward movement Inferior rectus (IR) – downward movement 3. Superior oblique (SO) – downward and outward movement Inferior oblique (IO) – upward and outward movement Movement of the eyes requires that each muscle work together with its pair. 2 When one contracts, the opposite muscle relaxes. To focus on an object or target, all of the muscles of the eye must be balanced and working together. With nor- mal vision, both eyes are able to focus on one target. The brain then combines the two pictures into a single, three- dimensional image, which creates depth perception. How- ever, when one eye is out of alignment, the brain receives signals with two different pictures. In young children, the brain adapts to the image being misaligned and the child M U S C L E S O F T H E H U M A N E Y E Superior oblique (downward and outward movement) Inferior oblique (upward and outward movement) Inferior rectus (downward movement) Medial rectus (inward movement) Lateral rectus (outward movement) Superior rectus (upward movement) To focus on an objec t or target, all of the muscles of theeyemust bebalanced and working together. sees only the image from the straight, or better eye, causing the child to lose depth perception. 6 Three cranial nerves (III, IV and VI), controlled by the brain, manage movement of the eye muscles. 2 Strabismus surgery addresses the muscular problems of the eye (align- ment), not issues with the brain’s signals to the muscles or interpretation of the image. 7