Optic Chiasma and Bitemporal Hemianopia
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Questions and Answers

What is the outcome of the decussation of nerve fibers in the optic chiasma?

  • Left optic tract conveying impulses from the left visual field
  • Right optic tract conveying impulses from the left visual field (correct)
  • Right optic tract conveying impulses from the right visual field
  • Left optic tract conveying impulses from the right visual field
  • What is the requirement for binocular vision?

  • Complete crossing of the optic nerve fibers in the chiasma
  • Partial crossing of the optic nerve fibers in the chiasma (correct)
  • No crossing of the optic nerve fibers in the chiasma
  • Complete separation 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?

  • Bitemporal hemianopia
  • Heteronymous hemianopia
  • Monocular hemianopia
  • Homonymous hemianopia (correct)
  • What is the destination of the visual fibers in the optic tract?

    <p>Lateral geniculate body</p> Signup and view all the answers

    What is the characteristic of Wernicke hemianopic pupil?

    <p>The pupillary light reflex will be normal when the unaffected hemiretina is stimulated and absent when the involved hemiretina is stimulated</p> Signup and view all the answers

    What type of lesion may give rise to an afferent pupillary conduction defect?

    <p>Optic tract lesion</p> Signup and view all the answers

    What type of tumors can cause chiasmal disease?

    <p>All of the above</p> Signup and view all the answers

    What is the pathway of the pupillary fibers in the optic tract?

    <p>Through the brachium of the superior colliculus to the pretectal nuclei</p> Signup and view all the answers

    Which part of the retina contributes to the optic tract with uncrossed fibers?

    <p>Temporal hemiretina</p> Signup and view all the answers

    What is the result of the partial crossing of the optic nerve fibers in the optic chiasma?

    <p>Binocular vision</p> Signup and view all the answers

    Which type of disease can cause a lesion in the optic tract?

    <p>All of the above</p> Signup and view all the answers

    What is the effect of stimulating the unaffected hemiretina on the pupillary light reflex in a Wernicke hemianopic pupil?

    <p>Normal</p> Signup and view all the answers

    Which structure do the pupillary fibers leave the optic tract to reach?

    <p>Brachium of the superior colliculus</p> Signup and view all the answers

    What is the characteristic pupillary response in a Wernicke hemianopic pupil when light is shone from the hemianopic side?

    <p>Absent</p> Signup and view all the answers

    What is the location of the optic chiasma in relation to the optic tract?

    <p>Anterior to the optic tract</p> Signup and view all the answers

    What is the term for the type of hemianopia that results from a lesion in the optic chiasma?

    <p>Bitemporal hemianopia</p> Signup and view all the answers

    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.

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