1. 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.

2. 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.

3. ANATOMICAL DIAGRAM OF EYE MOVEMENTS
References: This diagram is also found in Gray’s Anatomy,
any British edition after 1974.

4. 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.

5. OUTLINE I. EYE LOOKS LATERALLY II. EYE LOOKS MEDIALLLY III. SUMMARY
IV. OTHER CLINICAL DESCRIPTIONS: TROCHLEAR
NERVE DAMAGE AND TEST

6. EXPLANATION FOR DIFFERENCE BETWEEN EYE MOVEMENTS CHART AND CARDINAL POINTS OF GAZE: AN EXAMPLE: Consider patient's right eye IO SR
Both SR and IO
act to raise eye
when eyes
are looking
straight ahead
RIGHT
EYE
NOSE
ANATOMICAL ACTION

7. EXPLANATION FOR DIFFERENCE BETWEEN EYE MOVEMENTS CHART AND CARDINAL POINTS OF GAZE: EYE LOOKS LATERALLY
Muscles work best when somewhat stretched, poorly when short SR IO
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
eye looks
laterally
NOSE
Note: orientation of SR contributes to this
effect: muscle pull is most direct when eye is abducted
ANATOMICAL ACTION

8. 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 SR IO
If SR is damaged,
patient cannot raise
eye when looking
laterally
eye looks
laterally
NOSE
ANATOMICAL ACTION

9. CONSIDER MOVEMENT OF PATIENT'S LEFT EYEIO SR SR IO
both SR and IO
act to raise eye
LEFT
EYE
NOSE
ANATOMICAL ACTION

10. EXPLANATION FOR DIFFERENCE BETWEEN EYE MOVEMENTS CHART AND CARDINAL POINTS OF GAZE: EYE LOOKS MEDIALLY
Muscles work best when somewhat stretched, poorly when short SR IO IO SR
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
eye looks
medially
NOSE
Note: orientation of IO contributes to this
effect: muscle pull is most direct when eye is adducted
ANATOMICAL ACTION

11. 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 SR IO IO SR
if IO is damaged,
patient cannot raise
eye when looking
medially
eye looks
medially
NOSE
ANATOMICAL ACTION

12. 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 IO IO SR
THIS DIAGRAM
SHOWS
DIRECTION
PHYSICIAN
ASKS
PATIENT
TO LOOK,
NOT DIRECTION
OF PULL
OF MUSCLE IR SO SO IR
CLINICAL TEST:
CARDINAL POINTS
OF GAZE
NOSE
Note: MR and LR are not different in diagrams as their pull is direct

13. 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

14. Note: The above is a reasonable explanation for the clinical tests (See also Snell, Clinical Anatomy, 7th Ed., pp ). 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.

15. TROCHLEAR NERVE DAMAGE
PARALYZE SUP.
OBLIQUE IN RIGHT EYE
RIGHT EYE RO-
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