neuroanatomy Neuroanatomy is the study of the structure and organization of the nervous system. In contrast to animals with radial symmetry, whose nervous system consists of a distributed network of cells, animals with bilateral symmetry have segregated, defi ...

, the optic tract () is a part of the

visual system The visual system comprises the sensory organ (the eye) and parts of the central nervous system (the retina containing photoreceptor cells, the optic nerve, the optic tract and the visual cortex) which gives organisms the sense of sight (th ...

in the

brain A brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as Visual perception, vision. I ...

. It is a continuation of the

optic nerve In neuroanatomy, the optic nerve, also known as the second cranial nerve, cranial nerve II, or simply CN II, is a paired cranial nerve that transmits visual information from the retina to the brain. In humans, the optic nerve is derived fro ...

that relays information from the optic chiasm to the ipsilateral

lateral geniculate nucleus In neuroanatomy, the lateral geniculate nucleus (LGN; also called the lateral geniculate body or lateral geniculate complex) is a structure in the thalamus and a key component of the mammalian visual pathway. It is a small, ovoid, ventral projec ...

(LGN), pretectal nuclei, and

superior colliculus In neuroanatomy, the superior colliculus () is a structure lying on the roof of the mammalian midbrain. In non-mammalian vertebrates, the homologous structure is known as the optic tectum, or optic lobe. The adjective form '' tectal'' is common ...

. It is composed of two individual tracts, the left optic tract and the right optic tract, each of which conveys visual information exclusive to its respective contralateral half of the

visual field The visual field is the "spatial array of visual sensations available to observation in introspectionist psychological experiments". Or simply, visual field can be defined as the entire area that can be seen when an eye is fixed straight at a poin ...

. Each of these tracts is derived from a combination of temporal and nasal

retina The retina (from la, rete "net") is the innermost, light-sensitive layer of tissue of the eye of most vertebrates and some molluscs. The optics of the eye create a focused two-dimensional image of the visual world on the retina, which the ...

l fibers from each eye that corresponds to one half of the visual field. In more specific terms, the optic tract contains fibers from the ipsilateral temporal hemiretina and contralateral nasal hemiretina.

Visual system

The optic tract carries retinal information relating to the whole visual field. Specifically, the left optic tract corresponds to the right visual field, while the right optic tract corresponds to the left visual field. To form the right visual field, temporal retinal fibers from the left eye and nasal retinal fibers from the right eye form the left optic tract, and to form the left visual field, temporal retinal fibers from the right eye and nasal retinal fibers from the left eye form the right optic tract.

Autonomics

Several autonomic ocular motor responses are consensual. The optic tract is primarily responsible for relaying visual information to the LGN, but it is also peripherally responsible for transducing these bilateral autonomic reflexes, including the

pupillary light reflex The pupillary light reflex (PLR) or photopupillary reflex is a reflex that controls the diameter of the pupil, in response to the intensity (luminance) of light that falls on the retinal ganglion cells of the retina in the back of the eye, ther ...

and pupillary dark reflex.

Pupillary light reflex

The pupillary light reflex is an autonomic reflex that controls pupil diameter to accommodate for increases in illumination as perceived by the retina. Higher light intensity causes pupil constriction, and the increase of light stimulation of one eye will cause pupillary constriction of both eyes. The neural circuitry of the pupillary light reflex includes the optic tract which joins the optic nerve to the brachium of the

Pupillary dark reflex

Similarly to the pupillary light reflex, the pupillary dark reflex is an autonomic reflex that controls pupil diameter to accommodate for decreases in illumination as perceived by the retina. Lower light intensity causes pupil dilation, and the decrease of light stimulation of one eye will cause pupillary dilation of both eyes. Similarly, the neural circuitry of the pupillary dark reflex includes the optic tract which joins the optic nerve to the hypothalamus.

Damage and pathologies

Lesions

Lesions in the optic tract correspond to visual field loss on the left or right half of the vertical midline, also known as

homonymous hemianopsia Hemianopsia, or hemianopia, is a visual field loss on the left or right side of the vertical midline. It can affect one eye but usually affects both eyes. Homonymous hemianopsia (or homonymous hemianopia) is hemianopic visual field loss on the s ...

. A lesion in the left optic tract will cause right-sided homonymous hemianopsia, while a lesion in the right optic tract will cause left-sided homonymous hemianopsia. Stroke, congenital defects, tumors, infection, and surgery are all possible causes of optic tract damage. Peripheral prism expanders and vision restitution therapy are often employed in patients with visual field loss resultant of permanent optic tract damage.Optic tract. Healthline Body Maps. Retrieved from: http://www.healthline.com/human-body-maps/optic-tract#3/12 (accessed Nov 1, 2013).

Split-brain

In certain

split-brain Split-brain or callosal syndrome is a type of disconnection syndrome when the corpus callosum connecting the two hemispheres of the brain is severed to some degree. It is an association of symptoms produced by disruption of, or interference wit ...

patients who have undergone a corpus callosotomy to treat severe epilepsy, the information from one optic tract does not get transmitted to both hemispheres. For instance, a split-brain patient shown an image in the left visual field will be unable to vocally name what has been seen as the speech-control center is in the left hemisphere of the brain.

Pupillary reflexes

Pupillary reflexes, particularly the pupillary light reflex, are a powerful diagnostic tool often employed in clinical and emergency medical practice. A lack of equal consensual pupillary constriction to a light stimulus, especially a Marcus Gunn pupil, can be indicative of optic nerve damage, brainstem death, or optic tract damage in between.

Additional images

File:Hippocampus (brain).jpg, Diagram of hippocampus File:lateral geniculate nucleus.png, Schematic diagram of the primate lateral geniculate nucleus. File:Gray689.png, Superficial dissection of brain-stem. Ventral view. File:Gray718.png, Coronal section of brain through intermediate mass of third ventricle. File:Gray719.png, Hind- and mid-brains; postero-lateral view. File:Gray722.png, Scheme showing central connections of the

s and optic tracts. File:Gray724.png, Base of brain. File:Gray730.png, Section of brain showing upper surface of temporal lobe. File:Gray745.png, Dissection showing the course of the cerebrospinal fibers. File:Human brainstem anterior view 2 description.JPG, Human brainstem anterior view File:Optic tract and optic nerve.jpg, Optic tract and optic nerve File:Slide2dd.JPG, Optic tract File:Slide2cuc.JPG, Cerebrum. Deep dissection. Inferior dissection. File:Slide2HOM.JPG, Cerebral peduncle, optic chasm, cerebral aqueduct. Inferior view. Deep dissection. File:Slide3HOM.JPG, Cerebral peduncle, optic chasm, cerebral aqueduct. Inferior view. Deep dissection. File:Slide2MIR.JPG, Cerebrum.Inferior view.Deep dissection. File:Slide3MIR.JPG, Cerebrum.Inferior view.Deep dissection. File:Slide4MIR.JPG, Cerebrum.Inferior view.Deep dissection. File:Slide2ZEB.JPG, Cerebrum. Inferior view.Deep dissection File:Slide2ERV.JPG, Cerebrum. Inferior view.Deep dissection

References

{{DEFAULTSORT:Optic Tract Visual system Cerebrum