1. Conjugated Eye Movements Ákos Lukáts MD. PhD. (lukats@ana2.sote.hu)

2. Principles of eye movements
The image of an object should fall to roughly identical regions of the retina in the two eyes and should project to roughly the same part in the same the visual cortex. Small differences in projections are interpreted as spatial/positional information, big differences will lead to double image formation.
Result:
The movement of both eyes should be coordinated – focusing the same object.

3. Principles of eye movements II.
Conjugated eye movements
Requirements:
- muscles: 6 extraocular muscles ensure proper positioning the eye (4 rectus, 2 oblique + m. levator palpebrae superioris)
- innervations: n. III, n. IV, n. VI
- central pathways for eye movements, ensuring coordination

4. The Muscles

5. Orbital Anatomy and Muscle Function
axis of orbit
medial wall of the orbit runs in a paramedian sagittal plane
lateral wall deviates laterally
most muscles run almost parallel with the axis of orbit
The eye is approximately spherical and moves like a a free (ball and socket) joint with 3 main axis

7. Axis of the Eye and Possible Movements
Sagittal axis: medial and lateral rotation
Difficult to see, as the pupil is round in humans

8. Axis of the Eye and Possible Movements
Transverse axis: upward pull / elevation and downward pull / depression

9. Axis of the Eye and Possible Movements
Vertical axis: medial pull / adduction and lateral pull / abduction
Most muscles perform actions around all 3 axis.
Enough to know the precise insertion in relative to the axis to „guess” the possible movements

10. M. Rectus Lateralis
Acts only around the vertical axis: lateral pull / abduction
Innervation: n. VI.
m. rectus lateralis

11. M. Rectus Medialis
Acts only around the vertical axis: medial pull / adduction
Innervation: n. III.

12. M. Rectus Superior Vertical axis: medial pull /adduction
Transverse axis: upward pull /elevation
Sagittal axis: medial rotation
Innervation: n. III.
m. rectus superior

13. M. Rectus Inferior Vertical axis: medial pull / adduction
Transverse axis: downward pull / depression
Sagittal axis: lateral rotation
Innervation: n. III.
m. rectus inferior

14. M. Obliquus Superior Vertical axis: lateral pull / abduction
Transverse axis: downward pull / depression
Sagittal axis: medial rotation
Innervation: n. IV.

15. M. Obliquus Inferior Vertical axis: lateral pull / abduction
Transverse axis: upward pull / elevation
Sagittal axis: lateral rotation
Innervation: n. III.

16. Interplay of Muscle Function
To look up:
m. rectus superior
m. obliquus inferior X X X X

17. Interplay of Muscle Function
To look down:
m. rectus inferior
m. obliquus superior X X X X

18. The Innervations of Extraocular Muscles
n. III. – m. rectus superior
- m. rectus inferior
- m. rectus medialis
- m. obliquus inferior
- m. levator palpebrae superioris
(m. sphincter pupillae, m. ciliaris)
n. IV. - m. obliquus superior (trochlea)
(crosses before emergence from brainstem!)
n. VI. - m. rectus lateralis (abduction)

19. Paresis of external muscles
n. VI. paresis: m. rectus lateralis paralyzed, other muscles pull the effected eye medially
Double image, characteristic position of the head
N. IV. paresis (not shown): m. obliquus superior paralyzed other muscles pull the effected eye medially and upwards
Double image, characteristic position of the head

20. Paresis of external muscles
n. III. paresis
only the rectus lateralis and obliquus superior muscles are working, the eye is moved laterally and downwards
m. lev. palp. sup. paralyzed, the eyelid drops
m. sphincter pup. paralyzed, pupil dilatates, no light response
m. ciliaris paralyzed, no accommodation, eye focused to infinity
double image

21. Regulation of Conjugated Eye Movements: Cortex
Cortical center: Br No. 8 frontal eye field (frontal gaze center)
Activation of the center on the right side turns both of the eyes to the left.
R: m. rectus medialis
(n. III.)
L: m. rectus lateralis
(n. VI.)
Posterior view!

22. Recrossing fibers to nucl. III. run in FLM
The cortex do not directly influence cranial nerve nuclei: pontine gaze center of the opposite side
Recrossing fibers to nucl. III. run in FLM
Similar, but more complicated pathway for vertical eye movements
oculomotor nucleus
FLM: longitudinal medial fascicule
pontine horizontal gaze center
abducent nucleus
Anterior view!
R: m. rectus medialis
(n. III.)
L: m. rectus lateralis
(n. VI.)

23. Regulation of Conjugated Eye Movements: Other Pathways
Superior Colliculus – tectospinal tract – especially visually oriented: automatic follow of objects in visual field
Vestibular system and the brainstem exerts its influence through the FLM also
(nistagmus, automatic correction for passive movements, nonvisual stimulation)

24. Mesencephalon subst. grisea cent. n. mesenceph. n. V.
fasc. longitud. med
tectum
fasc. longitud. dors
formatio reticularis
CGM+brach coll. inf.
tr. tectospinalis
lemn. med.
tegmentum
tr. temp.-
occ.-pont.
n. ruber
tr. corticospinalis
crus
tr. fronto-
pont.
n. III.+n. Edinger Westphal

25. Convergence
When looking to nearby objects, the two eyes must turn towards each other: convergence
M. rectus medialis is activated on both side
Usually goes together with:
- accommodation (focusing)
- pupil contraction
Pupil contraction could be achieved by:
- light
- accommodation
- convergence
Have to be sure which one is examined!

26. To Keep Our Eyes Open
Opening the eye: m. levator palpebrae superioris (n. III.)
Closing the eye: m. orbicularis oculi (n. VII.)
Cornea reflex: irritation (touching) of the cornea will result in closing the eye to protect it.
Sensory part: n. V/1
Motor part: n. VII.

28. Literature
Ross MH. Histology. A Text and Atlas (Lippincott Williams and Wilkins, Philadelphia, 2003)
Moore KL, Dalley AF. Clinically Oriented Anatomy (Lippincott Williams and Wilkins, Philadelphia, 1999)
Oyster CW. The Human Eye (Sinauer Associates, Inc. (Sunderland, Massachusetts, 1999)
Wright KW. Textbook of Ophthalmology (Williams and Wilkins, Baltimore, 1997)
Carlson BM. Human Embryology and Developmental Biology (Mosby, Philadelphia, 2004)
Kandel ER, Schwartz JH, Jessell TM. Principles of Neural Science (McGraw Hill, New York, 2000)
Purves D. et al: Neuroscience, 3rd ed. Sinauer Associates, Inc, 2004