Musculus rectus medialis
The medial rectus originates from the common tendinous ring around the optic foramen and inserts on the medial sclera of the eyeball. Its action is to adduct the eyeball (rotate it nasally). It is innervated by the oculomotor nerve (CN III).
Origin: Common tendinous ring around the optic foramen
Insertion: Medial sclera of the eyeball
Action: Adducts the eyeball (rotates nasally)
Innervation: Oculomotor nerve (CN III)
Isolated dysfunction is uncommon. Damage to the oculomotor nerve can affect adduction. More often evaluated as part of a full neurologic or ophthalmic examination.
## Overview Medial strabismus is an inward deviation of the eye. In some Appaloosas it can be a normal breed variation. Acute onset suggests paralysis of the lateral rectus muscle from cranial nerve
Abnormal eye position or movement after trauma should be checked by a veterinarian.
## Overview Medial strabismus is an inward deviation of the eye. In some Appaloosas it can be a normal breed variation. Acute onset suggests paralysis of the lateral rectus muscle from cranial nerve VI damage, which can result from brain disease, equine protozoal myeloencephalitis, or trauma. ## Causes Congenital variation or acquired abducens nerve paralysis. ## Diagnosis Observation of eye position, neurologic examination, and further testing if acute or accompanied by other neurologic signs. ## Treatment None for congenital variation. Treat the underlying neurologic disease if acquired. ## Recovery and Prognosis Depends on the cause. Congenital cases are static. Acquired cases vary with the primary disease. ## Prevention Depends on etiology. Signs include: eye turned inward; may be normal in some Appaloosas; acute onset suggests cranial nerve VI damage
Isolated dysfunction is uncommon. Damage to the oculomotor nerve can affect adduction. More often evaluated as part of a full neurologic or ophthalmic examination.
Abnormal eye position or movement after trauma should be checked by a veterinarian.
See the Medial Rectus on our interactive 3D horse model. Open 3D Model