Chapter 38

OCULAR MOTOR SYSTEM

John A. Long and Thomas M. Tann

Ocular and orbital trauma frequently involves neurologic damage. In addition to containing the eye, the orbit is tightly packed with ocular support structures, including nerves, blood vessels, muscles, and fat. Concurrent trauma to the globe and orbit may easily become an “orbital multisystem trauma.” The treatment of orbital and globe injuries requires a thorough knowledge of the ocular motor systems.

EPIDEMIOLOGY (USEIR DATA)

Rate of extraocular muscle involvement among all serious injuries: 3%.

Age (years):

• range: 2–81;

• average: 26;

• rate of 0- to 9-year-olds among the total: 10%;

• rate of 10- to 19-year-olds among the total: 20%;

• rate of ≥60-year-olds among the total: 6%.

Sex: 80% male.

Place of injury:

• home: 32%;

• street and highway: 22%;

• recreation and sport: 14%;

• industrial premises: 13%;

• public building: 5%.

Source of injury:

• various blunt objects: 32%;

• various sharp objects: 15%;

• MVC: 15%;

• gunshot: 14%;

• BB/pellet gun: 6%;

• fall: 5%.

Globe involvement among the total: 50%.

PATHOPHYSIOLOGY

The globe and orbit are innervated by 6 of the 12 cranial nerves. The anatomy of the nerve pathways and origins has been well described and may be significant for the evaluation of patients and their management. The involved nerves are:

• II (optic);

• III (oculomotor);

• IV (trochlear);

• V (trigemineal);

• VI (abducens); and

• VII (facial)

EVALUATION

Examination of patients in an ER setting always involves an assessment of the neurologic system.

• A detailed history will often guide subsequent steps of the examination. In patients with orbital injuries, extra care must be taken to evaluate for nerve damage.

• The visual acuity is crucial to take in the orbital trauma victim. Vision testing and the swinging-flashlight test (see Chapters 9 and 37) will establish whether the optic nerve is functioning, and whether symmetrically.

• An equally important neurologic test is the pupillary examination (see Chapter 3, 9, and 37). An APD indicates that the optic nerve is disrupted somewhere anterior to the chiasm; this should instigate further investigation, including an orbital CT scan.

• Evaluation of the extraocular muscles’ movement can reveal information about cranial nerves III, IV, and VI.

• If extraocular muscle movement abnormalities are seen in a traumatic setting, further radiologic investigation should be initiated. One exception to this is the simple blowout fracture, which may be diagnosed clinically (see Chapter 36). Radiologic examination of patients with obvious blowout fractures may be delayed for 1 week, pending the spontaneous resolution of symptoms. If the diplopia and restrictive strabismus seen in simple blowout fractures resolve, then an orbital CT scan is not necessary (see Chapter 36).

• In cases of orbital injury involving neurologic damage, a CT scan is the radiologic test of choice. The relationship between the bones and soft tissues of the orbits is best delineated with a CT scan. The CT scan is also the most useful radiologic test for pre-operative surgical planning.

• Neurological injury to the orbit is almost always associated with trauma to the surrounding tissue(s). The neurological assessment of the globe and orbital injuries must be part of a comprehensive evaluation of the patient.

CLINICAL CONDITIONS

TON

See Chapter 37.

Bell’s Palsy

Pathophysiology

Because it has an extensive superficial plexus, the facial nerve is rather susceptible to trauma. The nerve exits the skull at the stylomastoid foramen and innervates the muscles of facial expression. The facial nerve innervates the orbicularis oculi muscle, and its dysfunction leads to Bell’s palsy.

Diagnosis

The clinical appearance is one of facial paralysis. In traumatic cases, lacerations or evidence of contusion trauma are usually found. Ocular manifestations of Bell’s palsy include:

• ectropion;

• lagophthalmos;

• brow ptosis; and

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