Vision is an important sense on our body. The visual fields we see are formed on the retina and the information goes to the visual cortex.

1. VISUAL PATHWAY AND ITS
DEFECTS

2. VISUAL PATHWAY
 The visual system is specialized to take visual
information and compose them into coherent
picture of our world. It begins in the eye where
the visual fields are formed on the retina, due
to refractive power of the cornea that lead to
the inversion of the image on the retina.

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 As shown above on the image, the right visual
field projects to the left side of visual cortex
and the left visual field projects to the right side
of the visual cortex.
 Retinal fibers are nasal and temporal fibers.
Nasal retina represent the temporal visual field
while temporal retina represent nasal visual
field.

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 Temporal retinal fibers pass the optic nerve
down to the optic tract ipsilateraly to the lateral
geniculate body in the thalamus, where the will
synapse with other neuron before projected to
the optic radiation and then to the primary
visual cortex.
 Nasal retinal fibers pass the optic nerve and
cross the optic chiasma and move
contralateraly to the optic tract of the other eye
and then down to LGN where it’s going to
synapse and move down to optic radiation to
the primary visual cortex.

6. Upper and Lower fields
projection to the cortex
 Fibers of the upper retina contains information
from lower visual field. They travel along the
optic nerve to the optic tract and then up to the
LGN where they synapse.
 Fibers of the lower retina contains information
from upper visual field, and they travel along
the CN II the same way as of upper retinal
fibers to the LGN and then synapses.

7. Cont…..
 Fibers from upper retina project directly to the
primary visual field which is superiorly to the
calculine fissure.
 Fibers from lower retina, their way to the
primary visual cortex is blocked by the inferior
horn of lateral ventricle. So, they swing around
the inferior horn to reach the primary visual
cortex that is inferiorly to the calculine fissure.
The swing fibers are called Meyer’s loop.

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 Meyer’s loop has clinical importance because
any lesion in the temporal lobe can lead to
upper visual field deficit.
 From the primary visual cortex, fibers go in
dorsal stream from the occipital lobe to the
parietal lobe up to frontal association areas.
This helps to know where things are and how
they are.
 In a ventral stream, fibers will go from occipital
lobe to the temporal association areas which
tells object recognition.

9. Visual pathway defects
 The visual pathway can be impaired by
different pathologies like tumors, trauma,
 ANOPIA: This is when there is a lesion at the
level of optic nerve of one eye, which means
that both temporal and nasal retinal fibers are
blocked and therefore no information from the
eye is perceived.
 Bitemporal hemianopia: This is when there
is a lesion at the level of optic chiasm. The
nasal retinal fibers that carries information
from temporal visual field have been impaired.

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When there is a lesion that compresses the
temporal retinal fibers of the right eye and
nasal retinal fibers of the left eye, and it is at
the level of right optic tract, it’s called
Homonymous hemianopia.
A lesion at the level of the optic radiation is
called Quadrantanopia, it may be superior or
inferior depending on the part affected.

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12. THANK YOU!