Visual Pathway Flashcards
How does the fovea appear on an opthalmoscope projection?
Darker shading on the orange retina
What is the photoreceptor make up like at the fovea?
Only cones
How do you measure if one’s visual field is reduced?
Perimetry test
What is a visual field?
The entire area you can see with one eye without moving it
Where do the optic nerves join?
At the optic chiasma
After meeting at the optic chiasma, fibres of the optic nerve split again and go where?
After that?
To the LGB / LGN of the thalamus (lateral geniculate body / nucleus)
Then move as optic radiation to cerebral hemisphere (occipital lobe)
At the optic chiasma what happens to fibres from optic nerve?
The nasal (medial) fibres of each nerve cross to the opposite side
So the fibres that move to the LGB contain the temporal fibres from the ipsilateral eye, and the nasal fibres from the contralateral eye
Where is the optic chiasma in the brain?
Just superior to the pituitary gland on the sphenoid bone
Why does the right visual cortex see the left visual field and vice versa?
- Because when you focus on something your eyes converge
- this convergence causes the visual field on that side to be seen by the nasal portion of the retina on that side, and the temporal part of the retina on the contralateral side
- When the crossover occurs at the chiasma, these fields are combined - but the lateral side doesn’t switch despite seeing the contralateral field of view
- So the sides are inverted
- Fuck me I hope that makes sense
What happens if the optic nerve is damaged on one side?
There is blindness in that eye
What happens if the crossover at the chiasma is damaged?
There is Bi-temporal hemianopia
Can only see the middle field of view because the nasal feedback from each eye doesn’t reach
What happens if the optic tract past the chiasma is damaged?
Contralateral homonymous hemianopia
Missing the field of view from the contralateral side
