German Contact Help Login Register

The Optic Tract

Contents

Introduction

The axons of the retinal ganglion cells converge to form the optic nerve, which after a partial decussation at the optic chiasm forms the optic tract. The optic tract is an important part of the visual pathway. Almost all of the axons of the left and right and left optic tracts synapse with the cells of the ipsilateral lateral geniculate nucleus. The efferent fibres emerge as the optic radiation and ultimately travel to the primary visual cortex.

Basal view of the brain
Recommended video: Basal view of the brain
Structures seen on the basal view of the brain with the brainstem removed, showing the cut surface of mesencephalon.

Anatomy

Optic chiasm

Optic chasm - caudal viewThe optic tract arises from the optic chiasm, which lies in the subarachnoid space above the pituitary gland. The optic nerve just behind the eyeball, contains the temporal and nasal fibres which are situated on their respective sides. Near the optic chiasma the macular fibres are central, becoming superoposterior within the chiasm. The nasal fibres cross and join the axons of the contralateral hemitemporal retina in the chiasma. The crossed fibres are in a greater number (53%) compared to the uncrossed fibres (47%).

Optic tract

Each optic tract contains the fibres from the ipsilateral temporal and contralateral nasal retina. Thus, the right optic tract contains fibres from the right halves of the right and left retinae, and the left optic tract from the left halves of the right and left retinae of the eyeballs. In other words, all optic nerve fibres carrying impulses relating to the left half of the field of vision are brought together in the right optic tract and vice versa, ensuring bilateral vision.

Optic tract - cranial view

The fibres from the lower retinal quadrants lie laterally, while upper retinal fibres go medially. The macular fibres are positioned dorsolaterally in the optic tract. Most of the optic tract fibres synapse in the lateral geniculate body, while a few of the fibres concerned with the light reflexes pass to the pretectal nucleus and superior colliculus. There is a retinotopic organization in the lateral geniculate nucleus. Fibres from the superior and inferior parts of the retina go to the medial and lateral horns respectively, while macular vision is represented in the hilum. There are six neuronal layers in the lateral geniculate nucleus, uncrossed fibres (temporal retina) synapse in layers 2,3 and 5, while crossed axons synapse in neuronal layers 1,4 and 6. Optic radiation and visual impulses commence here. They are ultimately interpreted in the primary visual areas of the cerebral cortex and an appropriate response is relayed. The optic radiation, also known as the geniculo-calcarine tract, is a relay centre receiving about 80% of the optic tract. The remaining fibres of the optic tract terminate in the pretectal nuclei and superior colliculus.

Blood supply

The blood supply to the optic tract is variable but typically arises from anastomotic branches of the posterior communicating and anterior choroidal arteries, together with branches from the middle cerebral arteries.

The venous drainage is from the superior aspect through the anterior cerebral veins and from the inferior aspect through the basal vein.

Get me the rest of this article for free
Create your account and you’ll be able to see the rest of this article, plus videos and a quiz to help you memorize the information, all for free. You’ll also get access to articles, videos, and quizzes about dozens of other anatomy systems.
Create your free account ➞
Show references

References:

  • Duong H, MD: Visual System Anatomy. WebMD LLC (accessed 12/01/2016).
  • S. D. Kenneth: Anatomy & Physiology: The Unity of Form and Function. 5th ed. (2010), New York: McGraw-Hill.
  • Lateral geniculate body. Encyclopædia Britannica, Inc. (accessed 12/01/2016).
  • Aldugman s: Optic Pathway. Fastbleep Ltd. (accessed 12/01/2016).
  • Optic tract. Encyclopædia Britannica, Inc. (accessed 12/01/2016).
  • Healthline Medical Team: Optic tract. Healthline Media (accessed 12/01/2016).
  • Prasad, S., Galetta, S.L., 2011. Anatomy and physiology of the afferent visual system. Handb. Clin. Neurol. 102, 3–19.

Author, Review and Layout:

  • Benjamin Aghoghovwia
  • Uruj Zehra
  • Catarina Chaves

Illustrators:

  • Optic chasm - caudal view - Paul Kim
  • Optic tract - cranial view - Paul Kim
© Unless stated otherwise, all content, including illustrations are exclusive property of Kenhub GmbH, and are protected by German and international copyright laws. All rights reserved.

Continue your learning

Article (You are here)
Other articles
Well done!
Create your free account.
Start learning anatomy in less than 60 seconds.