DIFFERENCES BETWEEN ANATOMICAL
DESCRIPTIONS OF ACTIONS OF EXTRAOCULAR
MUSCLES AND CLINICAL TESTS OF THEIR
FUNCTION
SUMMARY: The anatomical description of the actions
of eye muscles delineates the movements each muscle
produces. The clinical exam of eye movements shows
directions the patient is asked to move the eye to test
for deficits in muscles and nerves. The clinical tests
are empirically derived. Differences in the descriptions
reflect the fact that movements of elevation and
depression are produced by combinations of muscles.
DIFFERENCES BETWEEN ANATOMICAL
DESCRIPTIONS OF ACTIONS OF EXTRAOCULAR
MUSCLES AND CLINICAL TESTS OF THEIR
FUNCTION
1- In a person, movements of the eye in elevation and
depression (raising and lowering the eye) result from
the concerted actions of multiple eye muscles.
2- ANATOMICAL: The anatomical descriptions of eye
movements is based upon the actions of individual
muscles.
3- CLINICAL: Clinical tests of function of the muscles
are based upon evaluations of patients' abilities after
nerve or muscle lesions.
ANATOMICAL DIAGRAM OF EYE MOVEMENTS
References: This diagram is also found in Gray’s Anatomy,
any British edition after 1974.
DIFFERENCES BETWEEN ANATOMICAL
DESCRIPTIONS OF ACTIONS OF EXTRAOCULAR
MUSCLES AND CLINICAL TESTS OF THEIR
FUNCTION
In clinical tests, two effects apparently predominate in
movements of elevation/depression (raise/lower):
1- Muscles work best when stretched
2- When looking straight ahead, the SR, IR, SO and IO
muscles all insert at an angle. When looking to the side
muscle orientations change so that some pull more
directly relative to line of sight.
OUTLINE
I. EYE LOOKS LATERALLY
II. EYE LOOKS MEDIALLLY
III. SUMMARY
IV. OTHER CLINICAL DESCRIPTIONS: TROCHLEAR
NERVE DAMAGE AND TEST
EXPLANATION FOR DIFFERENCE BETWEEN EYE
MOVEMENTS CHART AND CARDINAL POINTS
OF GAZE: AN EXAMPLE: Consider patient's right
eye
SR
IO
Both SR and IO
act to raise eye
when eyes
are looking
straight ahead
RIGHT
EYE
NOSE
ANATOMICAL ACTION
EXPLANATION FOR DIFFERENCE BETWEEN EYE
MOVEMENTS CHART AND CARDINAL POINTS
OF GAZE: EYE LOOKS LATERALLY
Muscles work best when somewhat stretched, poorly when short
IO
SR
eye looks
laterally
NOSE
ANATOMICAL ACTION
1) both SR and IO
act to raise eye
2) if have patient look
laterally IO becomes
short
3) if then have patient
raise eye (look up);
IO is too short but SR
is long
4) eye is then raised
by SR
Note: orientation of SR contributes to this
effect: muscle pull is most direct when eye is abducted
EXPLANATION FOR DIFFERENCE BETWEEN EYE
MOVEMENTS CHART AND CARDINAL POINTS
OF GAZE: EFFECT OF SR DAMAGE
Muscles work best when somewhat stretched, poorly when short
IO
SR
If SR is damaged,
patient cannot raise
eye when looking
laterally
eye looks
laterally
NOSE
ANATOMICAL ACTION
CONSIDER MOVEMENT OF PATIENT'S LEFT EYE
IO
SR
SR
IO
both SR and IO
act to raise eye
LEFT
EYE
NOSE
ANATOMICAL ACTION
EXPLANATION FOR DIFFERENCE BETWEEN EYE
MOVEMENTS CHART AND CARDINAL POINTS
OF GAZE: EYE LOOKS MEDIALLY
Muscles work best when somewhat stretched, poorly when short
IO
SR
SR
IO
eye looks
medially
NOSE
ANATOMICAL ACTION
1) both SR and IO
act to raise eye
2) if have patient look
medially SR becomes
short
3) if then have patient
raise eye (look up);
SR is too short but IO
is long
4) eye is then raised
by IO
Note: orientation of IO contributes to this
effect: muscle pull is most direct when eye is adducted
EXPLANATION FOR DIFFERENCE BETWEEN EYE
MOVEMENTS CHART AND CARDINAL POINTS
OF GAZE: EFFECT OF IO DAMAGE
Muscles work best when somewhat stretched, poorly when short
IO
SR
SR
IO
if IO is damaged,
patient cannot raise
eye when looking
medially
eye looks
medially
NOSE
ANATOMICAL ACTION
SAME EFFECTS WORK FOR IR AND SO: if
arrange arrows so that they show the direction
the patient is asked to look, get points of gaze
SR
IR
IO
SO
CLINICAL TEST:
CARDINAL POINTS
OF GAZE
IO
SO
NOSE
SR
IR
THIS DIAGRAM
SHOWS
DIRECTION
PHYSICIAN
ASKS
PATIENT
TO LOOK,
NOT DIRECTION
OF PULL
OF MUSCLE
Note: MR and LR are not different in
diagrams as their pull is direct
EXPLANATION FOR DIFFERENCE BETWEEN EYE
MOVEMENTS CHART AND CARDINAL POINTS
OF GAZE: if arrange arrows so that show
direction ask patient to look, get points of gaze
CLINICAL TEST: CARDINAL POINTS OF GAZE
Note: The above is a reasonable explanation for the
clinical tests (See also Snell, Clinical Anatomy, 7th
Ed., pp. 826-829). Other descriptions of effects of
nerve lesions more closely follow the anatomical
basis of their action. The next slide is a description
of the effects of Trochlear nerve lesion based upon
illustrations from a lecturer at Yale University. At
rest, the effects of Superior Oblique paralysis are
due to the unopposed lateral rotation of intact
muscles (like Medial Strabismus from damage to the
Lateral Rectus). Patient tilts his head to compensate
for chronic rotation of one eye. Also, the patient has
an inability to look down when the eye is adducted,
even though the anatomical action of the Superior
Oblique is to abduct the eye.
TROCHLEAR NERVE DAMAGE
PARALYZE SUP.
RIGHT EYE ROOBLIQUE IN RIGHT EYE TATED LATERALLY
TILT HEAD
SO BOTH EYES
ROTATED
COMPENSATION:
TILTING HEAD
ROTATES
LEFT EYE
MEDIALLY
SYMPTOMS: Extortion (outward rotation) of the affected
eye due to the unopposed action of the inferior oblique
muscle. Vertical diplopia (double vision) due to the
extorted eye. Weakness of downward gaze most noticeable
on medially directed eye. This is often reported as difficulty
in descending stairs. Head tilt: patient will often tilt his
head opposite the side of the affected eye in an attempt to
compensate for the outwardly rotated eye. However,
anatomical action is still to pull eye down and out and
rotate medially.
source: Yale University