Ocular Motor Disorders Flashcards
Nerves responsible for eye movement are
CN III Ocular motor
CN IV Trochlear
CN VI Abducens
Extraocular muscle function
, runs on a continuum from normal to weak to paralysis
Instead of using the suffix “plegia” and “paresis” to describe the state of muscle function, the terms “phoria” and “tropia” are used
Phoria
Indicates weakness of the muscle
The eye would drift but drifting is held in check by sensory fusion
Tropia
Indicates paralysis of the muscle
The eye drifts even when the person is focusing on a target
Prefixes indicate the direction of the misalignment
Eso Eye is deviating inward (crossed eyes) Esophoria or esotropia Exo Eye is deviating outward (wall eyes) Exophoria or exotropia Hyper Eye is deviating upward Hyperphoria or hypertropia Hypo Eye is deviating downward Hypophoria or hypotropia
Oculomotor Nerve (CN III)
The third cranial nerve supplies: levator muscle of the eyelid medial rectus superior rectus inferior rectus inferior oblique CN III constricts the pupil through its parasympathetic fibers that supply the smooth muscle of the ciliary body and the sphincter of the iris.
Acquired CN III Palsy
Sudden onset of binocular horizontal, vertical, or oblique diplopia
Ptosis or a droopy eyelid
Congenital CN III Palsy
Found in young children
May not complain of diplopia because they suppress the second image or because they have superimposed amblyopia
Often they are brought in by their parents, who have noticed ptosis or strabismus.
Amblyopia is the major complication of 3rd nerve palsy in children
CN III Palsy Eye examination
May have a partial or complete ptosis
The pupil may be dilated and poorly reactive, or dilated and non-reactive to light
Deficits in ipsilateral adduction (medial rectus), elevation (superior rectus, inferior oblique),and/ordepression (inferior rectus) may be present.
Complete 3rd nerve palsies
Considered complete if impairment of the majority of function of all the somatic branches of the oculomotor nerve is present and ptosis is complete or almost complete.
Complete 3rd nerve palsies usually are associated with a large-angle exotropia and hypotropia (down and out
CN3 Palsy Differential
Vasculopathic HTN Diabetes Tumor Congenital Aneurysm
CN III Palsy Neuroimaging
Neuroimaging is almost always necessary. The approach to neuroimaging varies depending upon age, and whether the 3rd nerve palsy is isolated, and the degree of involvement of the extraocular muscles and pupil.
Consultation with a neuroradiologist may be helpful in determining the optimal imaging modalities and the order of imaging, particularly when aneurysm is a consideration.
Treatment is directed at the underlying etiology. The goal is to maximize visual function, including ocular alignmen
Trochlear Nerve (CN IV)
The fourth cranial nerve has the longest intracranial course and is the only cranial nerve that has a dorsal exit from the brainstem. CN IV innervates:
superior oblique muscle
CN IV Palsy Clinical Presentation
Binocular vertical diplopiaand/or subjective tilting of objects (torsional diplopia)
Objects viewed in primary position or especially in down-gaze may appear double (when going down a flight of stairs so that the pt. does not know which step to select).
The patient may adopt an anomalous head position to avoid diplopia because torsional and vertical diplopia often improve with head tilting to the side opposite the paralyzed muscle
CN IV Palsy Eye Examination
Ipsilateral hypertropia (the involved eye is deviated upward “nasal upshoot”) is present because the action of the superior oblique muscle (to rotate downward) is weak. The deviation is greater when gaze is in the direction toward the weak muscle. Thus, a right fourth nerve palsy causes greater hypertropia in left gaze.
