## Overview Paralysis of cranial nerve III (oculomotor nerve) produces a combination of signs because the nerve supplies multiple extraocular muscles plus the pupil constrictor and eyelid elevator. Typical findings include ventrolateral strabismus (eye positioned down and out), ptosis (drooping upper eyelid), and a dilated pupil that responds poorly to light. Causes include trauma, brainstem disease, and space-occupying lesions. ## Causes Trauma, equine protozoal myeloencephalitis, brainstem masses, or polyneuritis. The evidence for frequency of each cause in horses is limited. ## Diagnosis Neurologic and ophthalmic examination demonstrating the characteristic triad of strabismus, ptosis, and mydriasis. Further diagnostics (cerebrospinal fluid analysis, imaging) seek the underlying lesion. ## Treatment Directed at the primary disease when identified. Supportive care protects the cornea if eyelid function is impaired. Specific nerve recovery is often incomplete. ## Recovery and Prognosis Guarded. Some traumatic or inflammatory cases improve partially; permanent deficits are common. ## Prevention None specific.
eye positioned down and out; drooping upper eyelid; dilated pupil with poor light response; possible vision impairment
## Overview Paralysis of cranial nerve III (oculomotor nerve) produces a combination of signs because the nerve supplies multiple extraocular muscles plus the pupil constrictor and eyelid elevator. Typical findings include ventrolateral strabismus (eye positioned down and out), ptosis (drooping upper eyelid), and a dilated pupil that responds poorly to light. Causes include trauma, brainstem disease, and space-occupying lesions. ## Causes Trauma, equine protozoal myeloencephalitis, brainstem masses, or polyneuritis. The evidence for frequency of each cause in horses is limited. ## Diagnosis Neurologic and ophthalmic examination demonstrating the characteristic triad of strabismus, ptosis, and mydriasis. Further diagnostics (cerebrospinal fluid analysis, imaging) seek the underlying lesion. ## Treatment Directed at the primary disease when identified. Supportive care protects the cornea if eyelid function is impaired. Specific nerve recovery is often incomplete. ## Recovery and Prognosis Guarded. Some traumatic or inflammatory cases improve partially; permanent deficits are common. ## Prevention None specific.
eye positioned down and out; drooping upper eyelid; dilated pupil with poor light response; possible vision impairment