Visual Pathway Flashcards
What is your visual field?
everything you see with one eye (including your periphery) is your visual field
What is the yellow area?
And what is the darker area in the center?
yellow - optic nerve and contains no rods and cones so is a physiologicl dry spot
dark area - fovea centralis - large density of cones, thinnest part of the retina as the 10 layers of the retina move off to the side - the area you see see the best with
How is the visual field tested?
Visual field testing by confrontation test (Outpatient screening) or automated perimetry
Not to be confused with visual acuity testing (reading letters that gradually get smaller)
How are images form your visual field formed on your retina?
Images of objects in your field of vision is formed upside down and inverted on your retina
Describe the visual pathway?
All fibres from the eye pass through the optic nerve to the optic chiasma
At the optic chiasma the (medial) nasal fibres cross to the opposite side
So the optic tract contains fibres from the (lateral) temporal half of the ipsilateral eye and the crossed-over nasal fibres from the contralateral eye.
This corresponds to ALL fibres from the opposite half of the visual field
Fibres from the optic tract synapse at the LGB of the thalamus
From here the optic radiation passes behind the Internal capsule (retro-lentiform fibres) to reach the Primary Visual Cortex in the Occipital lobe (Area 17)
Thus the Right visual cortex sees the left half of the visual field and vice versa
At the optic chiasma, what fibres cross over to the opposite side?
nasal fibres
What side does the left and right sides of your visual fields go to?
Right half of visual field goes to left side and left half going to the right side
The optic chiasma is sitting on top of the pituitary gland so if it in englarged for some reason, like a tumour, what fibre would it hit and what vision would be lost?
it would affect the fibres that are crossing over at the chiasma therefore the nasal fibres which are ocming from the persons temporal field of view so temporal vision would be lost
What damage do you expect when different parts of the visual pathway are damaged?
Right optic nerve is damaged
blindness in one eye
What damage do you expect when different parts of the visual pathway are damaged?
optic chiasma disrupted in the middle
bitemporal hemianopia
What damage do you expect when different parts of the visual pathway are damaged?
right optic tract is damaged
contralateral homonymous hemianopia
What damage do you expect when different parts of the visual pathway are damaged?
optic radiation is damaged
contralateral homonymous hemianopia
