Optic Tract Terminations and Lateral Geniculate Body

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Questions and Answers

Where do the majority of the fibers from the optic tract terminate?

Pulvinar of the thalamus

Lateral geniculate body (correct)

Cortical layer 4

Optic radiations

Which layers of the LGB receive input from the ipsilateral eye?

Layers 1, 4, 6

Layers 1, 2, 3

Layers 2, 3, 5 (correct)

Layers 3, 4, 5

What is the name of the tract formed by the axons of the LGB reaching the cortex?

Pulvinar tract

Optic radiations

Geniculocalcarine tract

Both B and C (correct)

In which region of the occipital lobe do the fibers from the optic radiations terminate?

Calcarine fissure Signup and view all the answers

Which part of the optic radiation forms the loop of Meyer?

Lateral fibers Signup and view all the answers

Which region of the occipital lobe receives impulses from the upper/dorsal retinal field?

Cuneus Signup and view all the answers

What is unique about the lateral geniculate cells?

They have no binocular receptive fields Signup and view all the answers

What is the primary function of the Secondary Visual Association Area?

Visual processing and interpretation of what we see Signup and view all the answers

What is the term for the horizontal stripe of white matter within the gray matter of the Primary Visual Area?

Genari Line Signup and view all the answers

What type of visual loss is caused by a lesion in front of the optic chiasm?

Monocular scotoma Signup and view all the answers

What is the purpose of the Confrontation Test in ophthalmologic and neurologic assessment?

To assess visual field defects Signup and view all the answers

The following structures are involved in prechiasmatic lesion and chiasmatic lesions EXCEPT:

Lateral geniculate body Signup and view all the answers

What is the result of a lesion affecting the right optic nerve?

Total blindness of the right eye Signup and view all the answers

What is the term for the region of visual loss caused by a prechiasmatic lesion?

Scotoma Signup and view all the answers

What is the term for the preserved visual field of the maculae?

Macular Sparing Signup and view all the answers

Which structure is affected in Contralateral Homonymous Upper Qudrantic Anopsia?

Lingual Gyrus Signup and view all the answers

What is the result of the interruption of the optic radiations on one side as they pass through the loop of Meyer?

Pathways from the lower temporal quadrant of the ipsilateral retina and lower nasal quadrant of the contralateral retina are interrupted Signup and view all the answers

What is the term for the condition where the lesion is at the upper quadrant of the visual field?

Contralateral Homonymous Upper Quadrantic Anopsia Signup and view all the answers

Why is the macula spared in Lesion G?

Collateral vascular supply to the macular region Signup and view all the answers

What is the name of the pathway that is affected in Lesion F?

Lateral Optic Radiation Signup and view all the answers

What is the result of the contraction of the sphincter pupillae muscle?

Constriction of the pupils Signup and view all the answers

Where is the nucleus of the oculomotor nerve located?

At the level of the superior colliculus of the midbrain Signup and view all the answers

Which muscles are supplied by the lateral nucleus of the oculomotor nerve?

Superior, medial, and inferior recti, and inferior oblique Signup and view all the answers

Which nucleus of the oculomotor nerve supplies the ciliary muscle and sphincter pupillae?

Edinger-Westphal Nuclei Signup and view all the answers

Which nerve supplies the superior oblique muscle?

Trochlear nerve (CN IV) Signup and view all the answers

What is the function of the nucleus of Perlia?

Involved in convergence Signup and view all the answers

Which nucleus of the oculomotor nerve supplies the levator palpebrae superioris?

Nucleus of Perlia Signup and view all the answers

Where is the nucleus of the trochlear nerve located?

At the level of the inferior colliculus of the midbrain Signup and view all the answers

When the head turns to the left, what direction do the eyes look?

Right Signup and view all the answers

Which cranial nerve is responsible for transmitting impulses from the vestibular system to the brainstem?

CN VIII Signup and view all the answers

What is the purpose of the Doll's Eye Maneuver/Reflex?

To locate the lesion in a supranuclear, nuclear, or infranuclear region Signup and view all the answers

What is the normal finding in the Doll's Eye Maneuver/Reflex?

The head is rotated to the left, and the eyes look to the right Signup and view all the answers

During the examination of EOMs, what is the patient asked to follow?

The examiner's finger drawing a wide H Signup and view all the answers

What is the purpose of examining EOMs?

To assess conjugate eye movement Signup and view all the answers

What is the projection of the visual field on the retina?

Inverted and reversed Signup and view all the answers

What is the position of the patient during the Doll's Eye Maneuver/Reflex?

Supine Signup and view all the answers

Study Notes

Visual Association Areas

Primary Visual Area (BA 17) is also known as Striate Area due to the horizontal stripe of white matter (Genari Line) within the gray matter
Secondary Visual Association Area (BA 18,19) surrounds BA 17 and is involved in visual processing, including interpretation of what we see, saccade, ocular pursuit, accommodation, and convergence

Prechiasmatic Lesions

Lesions in front of the optic chiasm affect the retina and optic nerve (CN II)
Causes a monocular scotoma (circumscribed region of visual loss) or monocular visual loss, depending on the size and severity of the lesion

Clinical Correlation of Visual Field Examination

Confrontation Test is used for ophthalmologic and neurologic assessment of visual field defects
Can localize where the lesion is if there is a field defect

Chiasmatic Lesions

Vestibuloocular reflex pathway involves the vestibular system, CN VIII, and CN VI to regulate eye movement
Lesions at the optic chiasm affect both eyes, causing blindness or visual field defects in both eyes

Clinical Correlation of EOMs

Examination of EOMs involves having the patient follow the examiner’s finger as they draw a wide H or asterisk shape
Take note of the conjugate movement of the eyes
Doll’s Eye Maneuver/Reflex is done in an unconscious patient to check brainstem function for regulating eye movement

Occipital Gaze Center

The visual field is projected to the retina in an inverted and reversed manner

Termination of the Optic Tract

Lateral Geniculate Body (LGB) is an oval swelling projecting from the pulvinar of the thalamus
Receives input from the retina representing the contralateral visual field
Each LGB contains six layered neurons with each layer receiving input from only one eye
Optic tract fibers originating in the ipsilateral eye distribute to layers 2, 3, 5, and contralateral eye distribute to layers 1, 4, 6

Optic Radiations/Geniculocalcarine Tract

Fibers from the lateral part of LGB are directed downward and forward, then bend backwards in a sharp loop (Meyer’s Loop) passing through the temporal lobe and sweep posteriorly to the occipital lobe
Medial fibers take a more direct, non-looping course
Both (lateral and medial) fibers terminate in the cortical layer 4 of the upper and lower lips of the calcarine fissure in the occipital lobe

Anatomy of Optic & Extraocular Motor Pathways

Optic radiations/Geniculocalcarine tract fibers project to the lingual gyrus and cuneus
Lesions in the optic radiations can cause contralateral homonymous upper quadrantic anopsia or contralateral homonymous hemianopia with macular sparing

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Description

Learn about the terminations of the optic tract, specifically the Lateral Geniculate Body (LGB), its structure, and how it receives input from the retina. Understand the layers of the LGB and how they receive input from each eye. A must-know for anatomy and physiology students!