6.7 Visual Pathway

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Visual Pathways

Oliver Glenn C. Domingo, MD, PTRP, FPSOHNSDepartment of Anatomy, College of Medicine

UERMMMCI

REFERENCES• Snell, R.S. Clinical Neuroanatomy, 6th ed.,

Lippincott Williams & Wilkins, 2006.• Carague-Lansang, E.N., et al. Lansang Notes:

Modules in Neuroanatomy, 4th ed., UERMMMC: Quezon City, 2006.

• Moore, K.L. and Dalley, A. F. Clinically Oriented Anatomy, 5th ed., Lippincott Williams & Wilkins, 2006.

• Gilman, S. and Newman, S.W. Manter and Gatz’s Essentials of Clinical Neuroanatomy and Neurophysiology, 10th ed., F.A. Davis Co., 2003.

• Netter, F.H. Atlas of Human Anatomy, 4th ed., Elsevier Saunders, 2006.

Objectives

Demonstrate knowledge & understanding of the optic and visual pathway.

Demonstrate knowledge & understanding of the pupillary apparatus.

Demonstrate knowledge & understanding of the neuroanatomical basis of ocular movements.

Objectives

Describe the supranuclear mechanisms for ocular movement.

Trace the pathways involving the saccadic, smooth pursuit and vergence systems.

VISUAL SYSTEM

• Eye & Retina

• Optic nerves

• visual

pathways

OPTICAL COMPONENTS

• Cornea

• Pupillary opening of the iris

• Lens

• Retina

• Cornea• Aqueous humor

• lens• vitreous humor

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• FOVEA CENTRALIS

• - a small depression at the center of the macula lutea

• - cones

• PERIPHERAL RETINA

• - rods > cones

• PHYSIOLOGIC BLIND SPOT

• - corresponds to the optic disc which has no rods and cone

RETINA

RETINAL STRUCTURE

• Outer layer: rods and cones

• Middle layer: bipolar neurons: horizontal and amacrine.

• Inner layer:

• ganglion cells.

VISUAL PATHWAYS

MIDBRAIN

Bipolar neurons

VISUAL PATHWAY

VISUAL PATHWAY

• VISUAL FIELD

RETINAL FIELD

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Anatomy of visual pathwayRight eye Left eye

Temporal TemporalNasalNasal

RETINOGENICULOSTRIATEPATHWAY

Optic nerve

Nasal retina

Optic chiasm

Optic tract

Optic radiation

Temporal retina Temporal retina

Lateral Geniculate Body

LEFT

RIGHT HEMISPHERE

Optic nerve

Nasal retina

Optic chiasm

Optic tract

Optic radiation

Temporal retina Temporal retina

Lateral Geniculate Body

LATERAL GENICULATE NUCLEUS

• Nucleus in the thalamus

• 1° visual cortex

• laminated

LATERAL GENICULATE NUCLEUS

RETINOTROPIC ORGANIZATIONS

Projection on rightdorsal lateralgeniculate nucleus

Projection on leftdorsal lateralgeniculate nucleus

Projection onleft retina

Projection onright retina

OPTIC RADIATIONS

Optic Radiations and Projections to the Primary

Visual Cortex• Geniculocalcarine fibers

• Meyer’s loop–upper part of the

contralat visual field

• 1° cortex –Broadman’s Area 17

• Lines of Gennari–Layer 4

Stripe of Gennari in area 17

RETINOTOPIC REPRESENTATION OF THE VISUAL FIELDS

Calcarinesulcus

Calcarinesulcus

VISUAL FIELD DEFECTS(Lesions of optic pathway)

• What will happen if the left optic nerve is severed?

• What will happen if a person has a tumor in the pituitary gland (just below the optic chiasm) and the inner fibers are destroyed?

• What will happen if a person suffers a brain tumor on the right side of the brain around the lateral geniculate body?

CONFRONTATION TEST

VISUAL PATHWAYS

MIDBRAIN

Bipolar neurons

Connections of visual pathway with midbrain

• Pretectal nuclei–pupillary light reflex

• Superior Colliculus & Medial longitudinal fasciculus–lens accomodation, eye movements–other visual reflexes

ACCOMODATION REFLEX

ARGYLL ROBERTSON PUPIL

PUPILARY DILATATION

NeuroAnatomical Basis of Extraocular Movement

vertical axis

Horizontal axis

AP axis

YOKE MUSCLE COMBINATION

CONJUGATE EYE MOVEMENTS & THEIR

CONTROL• Conjugate Gaze–lateral–vertical gaze upward–vertical gaze downwad

• Vergence

• saccades

• smooth pursuit

• Vestibulo-ocular Reflex

CRANIAL NERVES CONCERNED WITH EYE MOVEMENT

SUPERIOR COLLICULUS

NEURAL BASES OF EXTRAOCULAR MOVEMENT

• Supranuclear level (cerebral hemispheres & brainstem)–Frontal gaze center (area 8):voluntary rapid eye

movement–Occipital gaze center (areas 18 & 19): smooth

pursuit movement–PPRF: center for lateral gaze–RiMLF(pretectal region near superior colliculus):

center for vertical eye movements

NEURAL BASES OF EXTRAOCULAR MOVEMENT

• Nuclear level–Nucleus of CN II and IV in the midbrain & CN VI in

the pons

• Infranuclear level–CN III, IV, VI

TYPES OF EYE MOVEMENT(PATHWAYS)

• Fast saccadic eye movement• Slow (SMOOTH) pursuit• Vergence eye movements• Vestibuloocular reflex (VOR) eye movements

SACCADIC SYSTEM

• Horizontal voluntary rapid eye movement–Broadman Area 8–contralateral PPRF–ipsilateral abducens nucleus

• ipsilat lateral Rectus

– via MLF– contralat occulomotor

nucleus–contralat medial rectus

SACCADIC SYSTEM

• Vertical voluntary rapid eye movement–Broadman Area 8–pretectal (RiMLF)–occulomotor nucleus

• SR, IR, IO

–trochlear nuclei• SO

SMOOTH PURSUIT

Broadman Area 18, 19

Retifular Formation

PPRF/RiMLF

ipsilat abducens nucleus

contralat oculomotor nucleus

Lateral RectusMedial Rectus

internal capsule

pons

trochear nuclei

oculomotor nuclei

Superior Oblique SR, IR, IO

SACCADIC AND SMOOTH PURSUIT SYSTEM

VESTIBULO-OCULAR REFLEX

DOLL’S EYE REFLEX

MEDIAL LONGITUDINAL FASCICULUS

Demonstrate knowledge & understanding of the optic and visual pathway.

Name the refractive media of the eye.

Trace the visual pathway (pathway of light to retinal photoreceptors to the primary visual cortex).

Describe the course and origin of optic nerve, chiasm and tract.

Illustrate the retinotopic organizations as it relates to the LGB and primary visual cortex

Illustrate the different visual field defects arising from lesions along the visual pathway.

Demonstrate knowledge & understanding of the pupillary apparatus.

Locate the Edinger-Westphal nucleus, pretectal nucleus and superior colliculus.

Trace the pathway for direct & consensual light reflex.

Trace the pathway for accomodation reflex.

enumerate the changes in the eye that occur during accomodation.

Demonstrate knowledge & understanding of the neuroanatomical basis of ocular

movements.

Describe the action of the extraocualr muscles in relation to conjugate gaze.

Describe the supranuclear mechanisms for ocular movement.

Trace the pathways involving the saccadic, smooth pursuit and vergence systems.

• Thank YouThank You