DR Medhat MRCP

II.
Optic nerve
• Pathway of vision :
- The receptors of vision are cones (for day vision) & rods (for night
vision) of the retina.
- From these receptors, the nerve fibers converge & pass through the
optic disc to form the optic nerve which contains nasal & temporal
fibers
‣ The nasal fibers decussate at the optic chiasma to pass in the
optic tract of the opposite side.
‣ The temporal fibers pass in the optic tract of the same side
- The fibers of optic tract relay in the lateral geniculate body from
which a new set of fibers arises & passes in the posterior limb of
internal capsule then fans out as optic radiation whose :
‣ Upper fibers (=Baum`s loop from inferior part of visual field)
run in the parietal lobe
‣ Lower fibers (=Myer`s fibers from superior part of visual
field) run in the temporal lobe.
- The fibers of optic radiation finally terminate at the area 17 in
occipital lobe (visual sensory area) where the images are percepted
while recognition & identification of the images is achieved in the
neighboring area 18 & 19 (visual psychic area).
19