Visual Pathway
Visual pathway or optic pathway is the nervous pathway that transmits impulses from retina visual
center in cerebral cortex.
1.
Light enters the eye and projects onto the retina, which contains photoreceptors:
o
o
Cones:

Operate in bright-light conditions

Responsible for visual acuity and color perception
Rods:

Operate in dim-light conditions

Responsible for low-light vision
Visual pathway
Signals from the retinal photoreceptors
Go to bipolar cells
Then to the ganglion cells
2.
Axons of the ganglion cells converge, forming the optic nerve (CN II).
3.
Optic nerve to the optic tract:
o
Optic chiasm (OC): where hemidecussation of optic nerve fibers occurs
o
Optic tract:

Nasal fibers from the left eye cross over to join the temporal fibers of the right
eye
right optic tract

Nasal fibers from the right eye cross over to join the temporal fibers of the left
eye
left optic tract
4.
From the optic tract, most fibers synapse in the lateral geniculate nucleus (LGN) of
the thalamus, with some going to the superior colliculus.
5.
From each LGN, neurons travel in the optic radiations (geniculocalcarine fibers):
o
o
6.
Inferior fibers:

Inferior radiation is on the lateral side (lateral bundle) of the optic radiations.

Nerves extend anteriorly around the temporal horn of the lateral ventricle
before proceeding posteriorly (Meyer’s loop).

Carry the information from the superior visual fields
Superior fibers:

The fibers that go superiorly, passing the parietal lobe, are on the medial side
of the optic radiations.

Carry the information from the inferior visual fields
Primary visual cortex (striate or calcarine cortex, or V1 or area 17):
o Optic radiations head posteriorly to the primary visual cortex.
o The primary visual cortex area is mostly in the medial brain surface of the occipital
lobe.
6:47
Eyeball and Retina
5:13
Primary Visual Cortex
Visual Fields
Anterior to the OC

Retina and optic nerve: carry visual information on the ipsilateral or same eye where the
nerve is located

OC:
o
Visual fields of each eye overlap considerably, to produce binocular vision and depth
perception.
o
The image from each half of the visual field is processed by the contralateral
hemisphere.
o
Left visual cortex (blue line) processes the information from the right half of the visual
field.
Right visual cortex (red line) processes the information from the left half of the visual
field.
o
o
In order for each hemisphere to receive visual information from the contralateral visual
field, the nasal fibers cross at the OC.
Diagram of the visual pathway and the visual fields: light enters the eye, sending signals to
the retina and through the optic nerve. The nasal fibers of each eye decussate at the optic chiasm,
continuing to the optic tract with the temporal fibers: right nasal fibers join the left temporal fibers
(blue lines) and the left nasal fibers join the right temporal fibers (red lines). Neurons synapse at the
lateral geniculate nucleus. Optic radiations connect the lateral geniculate nucleus to the primary visual
cortex of the occipital lobe where visual information is processed.
Image by Lecturio.
Posterior to the OC

Visual field information is processed in the contralateral hemisphere.

Optic tract and LGN:

o
Left visual field: represented by the right optic tract and LGN
o
Right visual field: represented by the left optic tract and LGN
Optic radiation and visual cortex:
o
From the LGN, neurons on both sides course to the visual cortex.
o
o
Inferior visual field:

Carried by the superior part of the optic radiations

Goes to the superior bank of the primary visual cortex
Superior visual field:

Carried by the inferior part of the optic radiations (through Meyer’s loop)

Goes to the inferior bank of the primary visual cortex