Conjugated Eye Movements Ákos Lukáts MD. PhD. (lukats@ana2.sote.hu) 2010.12.02.

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.

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

The Muscles

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

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

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

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

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

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

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

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

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

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

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

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

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)

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

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

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!

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.)

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)

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

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!

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.

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