Visual Pathway

what is a visual field

everything you see with one eye including in your periphery

anatomical pathway of the visual pathway

retina → optic nerve → optic chiasm → optic tract → lateral geniculate body → optic radiation → primary visual cortex

Right half of visual field form on left part of retina 

Left half of visual field form on right part of retina 

how is vision perceived in the occipital cortex of the brain?

all fibres from eye pass through optic nerve to optic chiasma

at optic chiasma the nasal fibres cross to the opposite side which means optic tract contains fibres from the temporal half of the same eye and cross over nasal fibres from the other eye – this corresponds to all fibres from the opposite half of the visual field (enough to see half of the world with one optic tract).

Fibres from the optic tract synapse at the lateral geniculate body of the thalamus, from here the optic radiation passes behind the internal capsule to reach the primary visual cortex in the occipital lobe.

Thus the right visual cortex sees the left half of the visual field and the left visual cortex sees the right of the visual field

pathway of light reflex

light falls on retina → impulses travel along optic nerve → optic chiasma → optic tract

fibres destined to activate pupillary reflex don’t go to lateral geniculate body but leave the optic tract to midbrain which is where CN III nucleus situated

Part of CN III nucleus is the edinger-westphal nucleus for parasympathetic fibres.

The pupillary reflex fibres go to edinger-westphal nucleus of both sides (afferent limb ).

from EWN → pre ganglionic parasympathetic pass through CN III into orbit → parasympathetic fibres go to synapse in ciliary and ganglion → post ganglionic fibres go through short ciliary nerves to constrictor pupillae, pupillary constrict on both side (efferent limb ) 

what would happen if the optic chiasma was disrupted in the middle

bitemporal hemianopia 

what would happen if right optic tract damaged?

contralateral homonymous hemianopia (half blindness on left visual field, R temporal L nasal)

if the blindness is on the left side, which side of the brain is it?

lesion on right side of brain

what would happen if optic radiation is damaged

contralateral homonymous hemianopia (blindness won't be symmetrical) 

what would happen if right optic nerve damaged

blindness in right eye