972
U N I T 1 0
Nervous System
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
Primary position: right esotropia
Left gaze: no deviation
Right gaze: left esotropia
Right hypertropia
Right exotropia
A
B
C
D
E
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.
TABLE 38-1
Innervation and Function of the Ocular Muscles
Muscle*
CN Innervation
Primary
Secondary
Tertiary
Medial rectus (MR)
III
Adduction
Lateral rectus (LR)
VI
Abduction
Superior rectus (SR)
III
Elevation
Intorsion
Adduction
Inferior rectus (IR)
III
Depression
Extorsion
Adduction
Superior oblique (SO)
IV
Intorsion
Depression
Abduction
Inferior oblique (IO)
III
Extorsion
Elevation
Abduction
*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.
LR
MR
IR
I0
SR
SO
MR
LR
SO
SR
I0
IR
