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Questions and Answers
What is the outcome of the decussation of nerve fibers in the optic chiasma?
What is the requirement for binocular vision?
What is the type of hemianopia that involves the same side of the field in both eyes?
What is the destination of the visual fibers in the optic tract?
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What is the characteristic of Wernicke hemianopic pupil?
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What type of lesion may give rise to an afferent pupillary conduction defect?
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What type of tumors can cause chiasmal disease?
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What is the pathway of the pupillary fibers in the optic tract?
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Which part of the retina contributes to the optic tract with uncrossed fibers?
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What is the result of the partial crossing of the optic nerve fibers in the optic chiasma?
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Which type of disease can cause a lesion in the optic tract?
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What is the effect of stimulating the unaffected hemiretina on the pupillary light reflex in a Wernicke hemianopic pupil?
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Which structure do the pupillary fibers leave the optic tract to reach?
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What is the characteristic pupillary response in a Wernicke hemianopic pupil when light is shone from the hemianopic side?
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What is the location of the optic chiasma in relation to the optic tract?
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What is the term for the type of hemianopia that results from a lesion in the optic chiasma?
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Study Notes
Optic Chiasma
- Fibers from the nasal (medial) half of the retina decussate within the chiasma and join uncrossed fibers from the temporal (lateral) half of the retina to form the optic tract.
- Decussation of nerve fibers in the chiasma results in the right optic tract conveying impulses from the left visual field and vice versa.
- Partial crossing of optic nerve fibers in the chiasma is a requirement for binocular vision.
Bitemporal Hemianopia
- Bitemporal hemianopia is a type of hemianopia caused by chiasmal disease.
Causes of Chiasmal Disease
- Neoplastic causes:
- Pituitary adenomas
- Craniopharyngioma
- Meningioma
- Glioma
- Nasopharyngeal tumors
- Metastases
- Non-neoplastic causes:
- Aneurysms
- Rathke pouch cysts
- Sphenoidal sinus mucoceles
- Arachnoid cysts
- Miscellaneous disorders:
- Demyelination
- Inflammation
- Trauma
- Radiation-induced necrosis
- Vasculitis
Optic Tract
- Each optic tract contains:
- Crossed fibers from the contralateral nasal hemiretina
- Uncrossed fibers from the ipsilateral temporal hemiretina
- Types of hemianopia (hemianopsia) involving the same side of the field in both eyes is homonymous.
Wernicke Hemianopic Pupil
- The optic tracts contain both visual and pupillomotor fibers.
- Visual fibers terminate in the lateral geniculate body.
- Pupillary fibers leave the optic tract anterior to the lateral geniculate body and project through the brachium of the superior colliculus to terminate in the pretectal nuclei.
- An optic tract lesion may give rise to an afferent pupillary conduction defect.
- Characteristics of Wernicke hemianopic pupillary reaction:
- Pupillary light reflex is normal when the unaffected hemiretina is stimulated.
- Pupillary light reflex is absent when the involved hemiretina is stimulated.
- Note: Wernicke hemianopic pupillary reaction is difficult to elicit due to scatter of light within the eye, requiring a fine beam of light.
Optic Chiasma
- Fibers from the nasal (medial) half of the retina decussate within the chiasma and join uncrossed fibers from the temporal (lateral) half of the retina to form the optic tract.
- Decussation of nerve fibers in the chiasma results in the right optic tract conveying impulses from the left visual field and vice versa.
- Partial crossing of optic nerve fibers in the chiasma is a requirement for binocular vision.
Bitemporal Hemianopia
- Bitemporal hemianopia is a type of hemianopia caused by chiasmal disease.
Causes of Chiasmal Disease
- Neoplastic causes:
- Pituitary adenomas
- Craniopharyngioma
- Meningioma
- Glioma
- Nasopharyngeal tumors
- Metastases
- Non-neoplastic causes:
- Aneurysms
- Rathke pouch cysts
- Sphenoidal sinus mucoceles
- Arachnoid cysts
- Miscellaneous disorders:
- Demyelination
- Inflammation
- Trauma
- Radiation-induced necrosis
- Vasculitis
Optic Tract
- Each optic tract contains:
- Crossed fibers from the contralateral nasal hemiretina
- Uncrossed fibers from the ipsilateral temporal hemiretina
- Types of hemianopia (hemianopsia) involving the same side of the field in both eyes is homonymous.
Wernicke Hemianopic Pupil
- The optic tracts contain both visual and pupillomotor fibers.
- Visual fibers terminate in the lateral geniculate body.
- Pupillary fibers leave the optic tract anterior to the lateral geniculate body and project through the brachium of the superior colliculus to terminate in the pretectal nuclei.
- An optic tract lesion may give rise to an afferent pupillary conduction defect.
- Characteristics of Wernicke hemianopic pupillary reaction:
- Pupillary light reflex is normal when the unaffected hemiretina is stimulated.
- Pupillary light reflex is absent when the involved hemiretina is stimulated.
- Note: Wernicke hemianopic pupillary reaction is difficult to elicit due to scatter of light within the eye, requiring a fine beam of light.
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Description
Learn about the optic chiasma, where nerve fibers decussate to form the optic tract, and bitemporal hemianopia, a type of hemianopia affecting the temporal visual fields.
