DIFFERENCES BETWEEN ANATOMICAL DESCRIPTIONS OF ACTIONS OF EXTRAOCULAR

MUSCLES AND CLINICAL TESTS OF THEIRFUNCTION

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 THEIRFUNCTION

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 THEIRFUNCTION

In clinical tests, two effects apparently predominate inmovements 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 sidemuscle 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: TROCHLEARNERVE DAMAGE AND TEST

NOSE

IO SR

EXPLANATION FOR DIFFERENCE BETWEEN EYE MOVEMENTS CHART AND CARDINAL POINTS OF GAZE: AN EXAMPLE: Consider patient's right eye

Both SR and IOact to raise eyewhen eyesare lookingstraight ahead

ANATOMICAL ACTION

RIGHTEYE

NOSE

1) both SR and IOact to raise eye2) if have patient looklaterally IO becomesshort3) if then have patient raise eye (look up); IO is too short but SR is long4) eye is then raised by SR

IO SRMuscles work best when somewhat stretched, poorly when short

EXPLANATION FOR DIFFERENCE BETWEEN EYE MOVEMENTS CHART AND CARDINAL POINTS OF GAZE: EYE LOOKS LATERALLY

eye lookslaterally

Note: orientation of SR contributes to thiseffect: muscle pull is most direct when eye is abductedANATOMICAL ACTION

NOSE

IO SRMuscles work best when somewhat stretched, poorly when short

EXPLANATION FOR DIFFERENCE BETWEEN EYE MOVEMENTS CHART AND CARDINAL POINTS OF GAZE: EFFECT OF SR DAMAGE

If SR is damaged,patient cannot raiseeye when looking laterally

eye lookslaterally

ANATOMICAL ACTION

NOSE

IO SR SR IO

both SR and IOact to raise eye

CONSIDER MOVEMENT OF PATIENT'S LEFT EYE

ANATOMICAL ACTION

LEFTEYE

NOSE

1) both SR and IOact to raise eye2) if have patient lookmedially SR becomesshort3) if then have patient raise eye (look up); SR is too short but IO is long4) eye is then raised by IO

IO SRMuscles work best when somewhat stretched, poorly when short

EXPLANATION FOR DIFFERENCE BETWEEN EYE MOVEMENTS CHART AND CARDINAL POINTS OF GAZE: EYE LOOKS MEDIALLY

SR IO

eye looksmedially

Note: orientation of IO contributes to thiseffect: muscle pull is most direct when eye is adductedANATOMICAL ACTION

NOSE

IO SRMuscles work best when somewhat stretched, poorly when short

EXPLANATION FOR DIFFERENCE BETWEEN EYE MOVEMENTS CHART AND CARDINAL POINTS OF GAZE: EFFECT OF IO DAMAGE

SR IOif IO is damaged,patient cannot raiseeye when looking medially

eye looksmedially

ANATOMICAL ACTION

NOSE

IOSR SRIO

THIS DIAGRAMSHOWSDIRECTIONPHYSICIANASKS PATIENTTO LOOK,NOT DIRECTIONOF PULL OF MUSCLE

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

IR IRSO SO

Note: MR and LR are not different in diagrams as their pull is direct

CLINICAL TEST:CARDINAL POINTSOF GAZE

EXPLANATION FOR DIFFERENCE BETWEEN EYE MOVEMENTS CHART AND CARDINAL POINTS OF GAZE: if arrange arrows so that showdirection 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.

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.

TROCHLEAR NERVE DAMAGETILT HEADSO BOTH EYESROTATED

RIGHT EYE RO-TATED LATERALLY

source: Yale University

PARALYZE SUP.OBLIQUE IN RIGHT EYE

COMPENSATION:TILTING HEADROTATESLEFT EYEMEDIALLY