Musculus rectus dorsalis
The dorsal rectus (superior rectus) is one of the four rectus muscles controlling eye movement. It originates from the orbital periosteum around the optic foramen (common tendinous ring) and inserts on the dorsal sclera of the eyeball. Its action is to rotate the eyeball dorsally (upward gaze). It is innervated by the oculomotor nerve (CN III). Together with the other extraocular muscles it allows the horse to direct its gaze. Isolated injury is rare; it is more often affected as part of orbital trauma, oculomotor-nerve disease, or generalized neurologic conditions.
Origin: Orbital periosteum around the optic foramen (common tendinous ring/annulus of Zinn)
Insertion: Dorsal sclera of the eyeball anterior to the equator
Action: Rotates the eyeball dorsally (looks up)
Innervation: Oculomotor nerve (CN III)
Strabismus or inability to move the eye upward can indicate oculomotor-nerve or muscle involvement. Evaluated as part of a cranial-nerve examination.
## Overview Strabismus is abnormal eye position. Damage to the oculomotor nerve (cranial nerve III) causes the eye to deviate downward and outward because the muscles that elevate and adduct the eye
Sudden abnormal eye position, inability to track objects upward, or other neurologic signs need prompt veterinary attention.
## Overview Strabismus is abnormal eye position. Damage to the oculomotor nerve (cranial nerve III) causes the eye to deviate downward and outward because the muscles that elevate and adduct the eye are paralyzed. Associated signs include a dilated pupil and drooping upper eyelid. Causes include equine protozoal myeloencephalitis, head trauma, or brain abscess. ## Causes Oculomotor nerve dysfunction from neurologic disease or trauma. ## Diagnosis Neurologic examination of eye position and pupil. ## Treatment Directed at the underlying neurologic disease. ## Recovery and Prognosis Depends on the cause. Some traumatic cases improve. Protozoal disease requires specific treatment. ## Prevention Depends on etiology. Signs include: eye deviated downward and outward; dilated pupil; drooping upper eyelid; may indicate equine protozoal myeloencephalitis, trauma, or abscess
Strabismus or inability to move the eye upward can indicate oculomotor-nerve or muscle involvement. Evaluated as part of a cranial-nerve examination.
Sudden abnormal eye position, inability to track objects upward, or other neurologic signs need prompt veterinary attention.
See the Dorsal Rectus (Superior Rectus) on our interactive 3D horse model. Open 3D Model