16 Questions
What is the outcome of the decussation of nerve fibers in the optic chiasma?
Right optic tract conveying impulses from the left visual field
What is the requirement for binocular vision?
Partial crossing of the optic nerve fibers in the chiasma
What is the type of hemianopia that involves the same side of the field in both eyes?
Homonymous hemianopia
What is the destination of the visual fibers in the optic tract?
Lateral geniculate body
What is the characteristic of Wernicke hemianopic pupil?
The pupillary light reflex will be normal when the unaffected hemiretina is stimulated and absent when the involved hemiretina is stimulated
What type of lesion may give rise to an afferent pupillary conduction defect?
Optic tract lesion
What type of tumors can cause chiasmal disease?
All of the above
What is the pathway of the pupillary fibers in the optic tract?
Through the brachium of the superior colliculus to the pretectal nuclei
Which part of the retina contributes to the optic tract with uncrossed fibers?
Temporal hemiretina
What is the result of the partial crossing of the optic nerve fibers in the optic chiasma?
Binocular vision
Which type of disease can cause a lesion in the optic tract?
All of the above
What is the effect of stimulating the unaffected hemiretina on the pupillary light reflex in a Wernicke hemianopic pupil?
Normal
Which structure do the pupillary fibers leave the optic tract to reach?
Brachium of the superior colliculus
What is the characteristic pupillary response in a Wernicke hemianopic pupil when light is shone from the hemianopic side?
Absent
What is the location of the optic chiasma in relation to the optic tract?
Anterior to the optic tract
What is the term for the type of hemianopia that results from a lesion in the optic chiasma?
Bitemporal hemianopia
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.
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.
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