Porth's Essentials of Pathophysiology, 4e

972

Nervous System

U N I T 1 0

I0

SR

SR

I0

LR

MR

MR

LR

SO

IR

IR

SO

TABLE 38-1 Innervation and Function of the Ocular Muscles Muscle* CN Innervation Primary

Secondary

Tertiary

Medial rectus (MR) Lateral rectus (LR) Superior rectus (SR) Inferior rectus (IR) Superior oblique (SO) Inferior oblique (IO)

III VI III III IV III

Adduction Abduction Elevation Depression Intorsion Extorsion

Intorsion Extorsion Depression

Adduction Adduction Abduction Abduction

Elevation

*In the schema of the functional roles of the six extraocular muscles, the major directional force applied by each muscle is indicated on the top.These muscles are arranged in functionally opposing pairs per eye and in parallel opposing pairs for conjugate movements of the two eyes. CN, cranial nerve.

standard terminology, the disorders of eye movement are described according to the direction of movement. Esotropia refers to medial deviation, exotropia to lateral deviation, hypertropia to upward deviation, hypotropia to downward deviation, and cyclotropia to torsional deviation (Fig. 38-16).

Nonparalytic Strabismus. Nonparalytic esotropia is the most common type of strabismus. The individual ocular muscles have no obvious defect and the amount of deviation is constant or relatively constant in the various directions of gaze. With persistent deviation, secondary abnormalities may develop because of

A

Primary position: right esotropia

C

B

Right gaze: left esotropia

Left gaze: no deviation

FIGURE 38-16. (A–C) Paralytic strabismus associated with paralysis of the right lateral rectus muscle: (A) primary position of the eyes (looking straight ahead); (B) left gaze with no deviation; (C) right gaze with left esotropia. (D) Primary position of the eyes with weakness of the right inferior rectus and right hypertropia. (E) Primary position of the eyes with weakness of the right medial rectus and right exotropia.

D

Right hypertropia

E

Right exotropia