Library · Anatomy
Visual pathway
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The image is not seen in the eye: it is seen in the brain. The visual pathway is the chain of structures that carries that information from the retina, the layer at the back of the eye that picks up light, to the primary visual cortex, which sits at the back of the head.
The route has named stops. It leaves the eye through the optic nerve, reaches the optic chiasm, continues along the optic tracts, stops at the lateral geniculate nuclei and ends by running along the optic radiations to the occipital lobe.
The most curious part happens at the chiasm. The fibers coming from the inner half of each retina, the nasal fibers, cross to the other side; the ones from the outer half, the temporal fibers, continue straight. That way each half of the brain ends up handling the opposite side of what you see.
Think of two highways that cross halfway and swap some of their lanes. That is why a lesion behind the chiasm knocks out the same half of the field in both eyes.
In brief
The visual pathway is the series of structures that carry visual information from the retina to the primary visual cortex.
It runs through the optic nerve, the chiasm, the optic tracts, the lateral geniculate nuclei and the optic radiations.
At the chiasm the nasal fibers cross and the temporal fibers continue straight: each hemisphere processes the opposite visual field.
Two highways that cross halfway and swap some of their lanes.
That is why a lesion behind the chiasm knocks out the same hemifield in both eyes.
Sources (1)
- National Center for Biotechnology Information, StatPearls PublishingNeuroanatomy, Visual Pathway, StatPearlsPublished
This page explains the topic in general terms; it does not tell anyone what treatment to follow.
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