Anat 6.7 Visual Pathways_Zulueta

Anatomy 6.7

February 21, 2012 Dr.Cristina Elma-Zulueta

Visual Pathways OUTLINE I. Anatomy of the Eyes and Optics II. Visual Pathways III. Visual Field A. Visual Field Defects IV. Visual Reflex Pathway A. Pupilary Light Reflex B. Accommodation Reflex C. Pupilary Dilatation V. Visual Pathways II A. Extraocular Muscles B. Cranial Nerves Concerned in Eye Movements C. EOMs Innervation D. Neural Bases of Extraocular Movement E. Medial Longitudinal Fasciculus F. Saccadic System G. Doll’s Eye Reflex

II. VISUAL PATHWAY  Retinal Field is the actual pathway o Something seen on the retinal field at the superotemporal side, it is projected in the inferonasal side on the visual field. This is due to the optical properties of the lens that will invert and reverse the image. - The image is INVERTED and REVERSED.

I. ANATOMY OF THE EYES AND OPTICS Light Cornea (greatest refractive index) Aqueous humor Lens Vitreous humor Retina (Transduction in the rod and cone cells; the only nervous part of the eye)

Fig 2:Visual Pathway Fig 1: Anatomy of the Eyes

 Ciliary muscle- contracts: thickening of the lens; suspensory ligament relaxes  Pupil- controlled by sphincter (constrict) and dilator (dilate) papillae  Retina: Ganglion cell layer- forms optic nerve o Cones – color vision and high visual acuity o Rods – light perception and low visual acuity with good contrast o Layers 4,6,7,8- the only layers with cell bodies  Fovea Centralis o A small depression at the center of the macula lutea o Area of the most acute vision o Only closed packed cones are present o Each cone projects to one ganglion cell mediating high resolution  Peripheral Retina o There are more rods than cones o Many project to a single ganglion cell mediating high light sensitivity but poor resolution  Physiologic Blind Spot o Temporal side of the macula lutea o Corresponds to the optic disc which has no rods and cones

Pathway: 1. Receptor – Photoreceptors: Rods and cones 2. N1 – bipolar neurons (Retina) 3. N2 – ganglion cells(Retina)  Axons of ganglion cell becomes the optic nerve. Fibers that arise from retina eventually goes to the Lateral Geniculate Body. (hearing and vetibular sys. – medial geniculate body)  Retinogeniculate fibers: (1)will form the optic nerve (2) join the optic chiasm (3) go to the optic tract Note: A small number of axons terminate in the suprachiasmatic nucleus of the hypothalamus (circadian rhythm). 4. N3 – Lateral Geniculate Body (LGB) of the Thalamus  Lateral projections at the LGB-Meyer’s Loop  Geniculocalcarine (from LGB to Calcarine cortex) geniculostriate fibers or optic radiation  Optical Tract ending in this prominence

or

Note: The area of the cortex that receives the optic radiations surrounds the calcarine fissure on the medial side of the occipital lobe. The cuneus, the gyrus above the calcarine fissure receives visual impulses from the upper quadrants of the retina / upper optic radiation. The lingual gyrus below the calcarine fissure receives visual impulses from the lower quadrants of the retina.

Group 8 안녕! |봉까, 보니파시오, 볼라짜, 브리에스, 브리오네스, G. J. & R., 붼아벤테

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5. Primary Visual Cortex o A.k.a. Striate Cortex – d/t heavy lamina of myelinated fibers at layer 4 = the stria or lines of Gennari o A.k.a. Broadmann Area 17, or Calcarine cortex o Influences from BA 17 are relayed to BA 18 and 19 (visual association areas) for interpretation of the images seen.

VF

RF Fig 3: Visual Field

A. VISUAL FIELD DEFECTS

Fig 3: Primary Visual Cortex

 At the optic chiasm: o Partial decussation: o Nasal fibers crosses over to contralateral side. o Temporal fibers remain ipsilateral.  After the chiasm: o Each fiber will contain the temporal fibers of the ipsilateral side and the nasal fibers of the contralateral side  REVIEW: o Light → Cornea → Aqueous humor → Lens → Vitreous humor → Retina → transduction of signal in photoreceptors → N1: bipolar neurons → N2: ganglion cells → optic nerve → @chiasm, crossing of nasal fibers and temporal fibers stay on same side → optic tract (ipsilateral temporal and contralateral nasal fibers) → N3: LGB → optic radiation → upper (end up in cuneus) and lower radiation (end up in lingual gyrus) → BA 17 → BA 18 & 19 for visual perception  Difference between Visual Field and retinal field: (1) Visual Field - corresponds to the environment viewed by each eye; final manifestation of the patient. eg. blind spot of the patient (2) Retinal Field – on the eye itself

Fig 4: Visual Field Defects

 Lesions in the Visual Pathway: Lesions along the pathway from the eye to the visual cortex result in deficits in the visual fields shown as black areas on the corresponding visual field diagram. Table 1. Lesions

III. VISUAL FIELD  Divided into 4 quadrants  The optical properties of the lens invert the projection of the visual field on the retina producing an inverted and reversed image on the retina.  Upper Retinal Quadrants- Lower Field of Vision  Lower Retinal Quadrants- Upper Field of Vision  Anything in the superior temporal quadrant in the visual field will be projected to the inferior nasal quadrant of the retinal field

LESION A. (R) Optic Nerve

B. Optic Chiasm

C. (R) Angle Of Chiasm D. (R) Optic Tract

E. (R) Optic Radiation F. (R) 1° Visual Cortex G. (R) Cuneus Group 8 안녕! |봉까, 보니파시오, 볼라짜, 브리에스, 브리오네스, G. J. & R., 붼아벤테

DEFECT (R) Eye Blindness Denervate the retina that will affect both temporal and nasal fibers forming the optic nerve Bitemporal Homonymous Hemianopsia Affects the right and left nasal retinal fibers. After the chiasm, everything is made up of the same fibers. (R) Nasal Hemianopsia Affects the right temporal retinal fibers Contralateral Homonymous Hemianopsia Affects right temporal retinal fibers and the left nasal retinal fibers (L) Homonymous Hemianopsia (L) Homonymous Superior Quadrantic Anopsia (L) Homonymous Inferior Quadrantic Anopsia

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H. (R) Meyer Loop (L) Homonymous Heminanopsia  Scotoma – an area lost of function in the visual field.  Macular Sparing –Since one cone is projected to one ganglion cell, the representation of the macula is very big (2/3) in the primary visual cortex. To injure the macula, you have to injure almost the whole visual cortex or it takes a massive injury or big occlusion to the primary visual cortex before the area of the macula is affected.  Homonymous- both right or both left fields  Heteronymous- both temporal fields affected Note: Macula Lutea is represented on the posterior part of B.A 17 and the periphery of the retina is represented anteriorly.

IV. VISUAL REFLEX PATHWAY A. PUPILARY LIGHT REFLEX  Shine a light from the side to elicit papillary light reflex -> stimulate optic nerve ->pupils of both eyes constrict (parasympathetic) -> contraction of sphincter pupillae muscles of the iris.  Afferent arm – Optic Nerve  Efferent arm – Oculomotor Nerve (innervate sphincter papillae  iris)  Direct reflex – response of stimulated eye  Consensual or indirect reflex – response of unstimulated eye due to posterior commisure that goes to contralateral side and affect the eye  Papillary dilatation - sympathetic Pathway: Optic nerve Optic chiasm Optic tract ↓ Pretectum (Posterior Commissure) ↓ Edinger-Westphal nucleus ↓ Oculomotor nerve ↓ Ciliary ganglion ↓ Sphincter pupillae

Fig 5: Pupillary Light Reflex

 Difference of visual pathway and pupillary light reflex pathway is that pupillary light reflex pathway will not pass to the LGB then impulses will go to the midbrain at area of pretectal nucleus.  Postganglionic parasympathetic fibers via short ciliary nerves innervate the sphincter papillae muscles. Long ciliary nerves will reach the constrictor papillae  Constriction on other side is due to the posterior commissure, which will cause impulses to reach the contralateral EdingerWestphal nucleus via the posterior commissure.  Case 1: Light was flashed on the right eye (+) Direct reflex; (-) Consensual reflex = impulses travel to the optic nerve, no problem in the R CN II, (+) direct reflex = have papillary constriction on the R, R CN III should be intact, (-) consensual reflex = no constriction of pupil on the left Defect: L Oculomotor nerve (Final effect did not reach L eye) Light was flashed on the left eye (-) Direct reflex;(+) Consensual reflex = light was seen by L CN II because you have consensual reflex, R CN III is ok (-) direct reflex= no constriction of the pupil on the L, L CN III problem  Case 2: Right eye (+) Direct reflex (+) Consensual reflex (+) Direct reflex = light seen by CN II, R CN III is okay; (+) Consensual reflex = L CN III is not the problem Left eye (-) Direct reflex (–) Consensual reflex = no impulses recognized by CN II Defect: L CN II  Case 3: Elicit blink reflex on the right, (+) Direct blink reflex(-) Consensual blink reflex = problem in L CN VII = impulses travel to the R CN V (+) Direct blink reflex = there’s a stimulation of the R orbicularisoculi innervated by R CN VII (-) Consensual blink reflex = problem in L CN VII Left eye (–) Direct blink reflex (+) Consensual blink reflex =have impulses travel to CN V because you have at least one reflex response, no direct blink so there’s really a problem in L CN VII Defect: L CN VII

B. ACCOMODATION REFLEX  Accommodation o Occurs when focusing on near objects Group 8 안녕! |봉까, 보니파시오, 볼라짜, 브리에스, 브리오네스, G. J. & R., 붼아벤테

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o miosis-pupil constriction o lens becoming more globular or more convex-contraction of ciliary muscle that causes relaxation of suspensory ligament of the lens o ocular convergence- contraction of medial rectus

corticobulbar and corticomesencephalic fibers go to the oculomotor nucleus to produce the reflex  Argyll Robertson Pupil - Lesion on periaquaductal gray of midbrain- more accommodation fibers than pupillary light fibers, (-) papillary light reflex, (+) normal accommodation  Difference between Pupillary and Accommodation Pathways o Impulses will not bypass the LGB. It will proceed the usual way up to the primary visual cortex and travel to areas 18 and 19 because there have to be some interpretations on what you are seeing. And areas 18 and 19 are the visual association areas where interpretation of what you will saw will occur. o Pupillary light reflex pathway will bypass the LGB, will immediately go to the superior colliculus. While accomodation reflex will have to reach the usual visual pathway but will also have to reach areas 18 and 19.

C. PUPILARY DILATATION 1. Due to low intensity light: Impulses from retina go to optic tract ↓ Superior Colliculus ↓ Tectospinal Tract (descending tract) ↓ Intermediolateral cell column T1 and T2 ↓ Preganglionic sympathetic fibers ascend sympathetic trunk ↓ Synapse at the superior cervical ganglion ↓ Carotid plexus (outside internal carotid artery) ↓ innervate Dilator papillae muscle (through long ciliary nerves)

Fig 6: Accomodation Reflex

Pathway: Area 17 ↓ Areas 18 and 19 ↓ Optic radiation ↓ Superior colliculus ↓ Pretectal area ↓ Edinger-Westphal nucleus

Ciliary ganglion (CN III)

NOTE: Long ciliary nerve (sympathetic fibers) vs. Short ciliary nerve (parasympathetic fibers)

Episcleral ganglion

Ciliary ms. (more convex lens)

CN III nucleus (Medial rectus) -convergence

Sphincter pupillae -contraction papillary ms.  Skip LGB – does not need fibers of the Meyer’s Loop and Optic Radiation  Will pass through the visual cortex because the person voluntary looks at the object  Nucleus of Perlia – one of the nuclei of the oculomotor nuclear complex stimulated other than the Edinger-Westphal nucleus during accommodation, responsible for ocular convergence.  Alternate Pathway for the Accommodation Reflex o Impulses from area 18 and 19 go to the motor cortex of the frontal lobe through the superior longitudinal fasciculus,

Fig 7: Pupilary Dilatation Pathway

 Pupillary dilation is a sympathetic response (ex. When you’re trying to see in a dark movie house)  Lesion of sympathetic supply of the eye → Horner’s syndrome: characterized by miosis, anhydrosis and pseudoptosis

Group 8 안녕! |봉까, 보니파시오, 볼라짜, 브리에스, 브리오네스, G. J. & R., 붼아벤테

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o Miosis: Predominant effect of parasympathetic innervation to the eye o Anhidrosis: face that is dry, red and warm o Pseudoptosis: Denervation of Muller’s muscle (associated wit levator palpebrae superioris that elevates the upper eye lid) 2. Due to severe pain (ciliospinal reflex) / strong emotional state pathway (example – watching a horror movie): Impulses reach the: a) Ciliospinal-tectobulbar tract – CN VII innervates the orbicularis oculi which causes closing of the eye Retina ↓ optic tract superior colliculus ↓ tectobulbar tract nuclei of facial nerves ↓ supplies orbicularis OCULI ↓ eye closure b) Superior colliculus ↓ tectospinal or reticulospinal tract Reticular formation ↓ Anterior horn cells of CERVICAL spinal cord ↓ Arm musculature (arms thrown upward across the face)

Fig 8: Extraocular Muscles

EXTRAOCULAR MUSCLES: YOKE MUSCLES LEFT RIGHT DIRECTION MR LR LEFT TO RIGHT LR MR RIGHT TO LEFT IO SR UP AND LEFT SR IO UP AND RIGHT SO IR DOWN AND LEFT IR SO DOWN AND RIGHT IO + SR SR + IO STRAIGHT UP SO + IR IR + SO STRAIGHT DOWN

V. VISUAL PATHWAYS II CONJUGATE MOVEMENTS  Movements o Lateral gaze o Vertical gaze upward o Vertical gaze downward  To permit accurate conjugate movements, the 12 EOMs, their 6 cranial nerves and nuclei and the MLF must operate as a unit  Lesion: diplopia or double vision

B. CRANIAL NERVES CONCERNED IN EYE MOVEMENTS

A. EXTRAOCULAR MUSCLES Muscle Superior Rectus Inferior Rectus Superior Oblique Inferior Oblique Medial Rectus Lateral Rectus Levator Palpebrae Superioris

Action(s) Elevation,Adduction,Intorsion Depression,Adduction,Extorsion Abduction,Depression,Intorsion Abduction, Elevation, Extorsion Adduction Abduction Elevation of Upper Eyelid

Nerve CN III CN III CN IV CN III CN III CN VI CN III

 REVIEW: o All muscles are innervated by CN III except: Superior Oblique (CN IV) and Lateral Rectus (CN VI) o All recti muscles are adductors except LR w/c is an abductor o All obliques are abductors including LR o All superior muscles are intorters o All inferior muscles are extorters o SO & IR are depressors o IO and SR are elevators

 Oculomotor Nerve (CN III) – located in the midbrain at the level of the superior colliculus. o Oculomotor nuclear complex: 1. Paired nuclei  Lateral nucleus to supply SR, IR, MR, IO  Edinger-Westphal nucleus, the parasympathetic component to supply the sphincter pupillae and ciliary muscles. 2.Midline nuclei  Caudal central nucleus to supply levator palpebrae superioris  Nucleus of Perlia: The “convergence” nucleus 3.Association nuclei  Nucleus of DARKSCHEWITSCH and interstitial nucleus of Cajal: associated with vertical eye movements  Trochlear Nerve (CN IV) – located in the midbrain at the level of the inferior colliculus. Supplies Superior Oblique. th  Abducens Nerve (CN VI) – located below the floor of the 4 ventricle at the junction of the pons and medulla. Supplies Lateral Rectus.

Group 8 안녕! |봉까, 보니파시오, 볼라짜, 브리에스, 브리오네스, G. J. & R., 붼아벤테

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1-2.NAME/DRAW VISUAL FIELD DEFECT AT THE LEVEL OF THE OPTIC CHIASM. 3. RIGHT OPTIC TRACT 4. LEFT LINGUAL GYRUS 5. AREA OF THE EYE WHERE THERE ARE NO RODS NOR CONES 6-8. 3 REFLEX CHANGES DURING ACCOMODATION 9. OCULOMOTOR NERVE NUCLEUS WHICH IS PARASYMPATHETIC(PUPILLARY LIGHT/ACCOMODATION REFLEX) 10. CN III NUCLEUS RESPONSIBLE FOR OCULAR CONVERGENCE

C. EOMs INNERVATION  Oculomotor Nerve o superior rectus o inferior rectus o inferior oblique o medial rectus o levator palpebrae superioris  Trochlear Nerve o superior oblique  Abducens Nerve o lateral rectus Fig 10: Neural Bases of Extraocular Movement

E. MEDIAL LONGITUDINAL FASCICULUS o Extends full length of the brainstem to upper cervical levels o Major fxn: control & coordination of eye movements o Visual inputs: PPRF and vestibular nuclei

F. SACCADIC SYSTEM

Fig 9: Extrinsic Eye Muscles, Innervation and Action

D. NEURAL BASES OF EXTRAOCULAR MOVEMENT  Supranuclear level (cerebral hemispheres & brainstem) o Frontal gaze center (area 8):voluntary rapid eye movement o Occipital gaze center (areas 18 & 19): smooth pursuit movement o PPRF: center for lateral gaze o RiMLF(pretectal region near superior colliculus): center - for vertical eye movements  Nuclear level o Nucleus of CN II and IV in the midbrain & CN VI in the pons  Infranuclear level o CN III, IV, VI

 Saccades: fast conjugate eye movements that place an object on the fovea.  Horizontal Voluntary Rapid Eye Movement o Impulse: area 8 o Corona radiata and anterior limb of internal capsule to reticular formation o Decussation in midbrain o PPRF o Abducens nucleus (supply ipsilateral LR) and via MLF to oculomotor nucleus (supply contralateral MR)  Vertical Voluntary Rapid Eye Movement o Impulse: area 8 o Corona radiata and anterior limb of internal capsule o Pretectal region at RiMLF o Some fibers cross (MLF); some do not o Oculomotor nuclei (supply SR, IR, IO) and Trochlear nuclei (supply SO)

G. DOLL’S EYE REFLEX  Done in unconscious patient  Head rotated to the right – eyes will move conjugately to the left  Indicates that the brainstem mechanisms for regulating eye movements are intact

Group 8 안녕! |봉까, 보니파시오, 볼라짜, 브리에스, 브리오네스, G. J. & R., 붼아벤테

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